What is a Plumeria Center Cut?

Center Cuts are an often-overlooked cutting that deserves a place in your garden! A center cut is a branch or branches without any growth tips. Treat center cuts as you would any cutting. When a center cut is planted buds will form towards the of the cutting from old leaf nodes and a new growth tip will form. Often several new tips will appear!

Because the single cutting forms multiple tips so quickly, center cuts are sometimes preferred to single tip cuttings. Another benefit to center cuts is the diameter is typically much larger than a tip cutting because of its age. It will makes a larger tree base than a tip cutting in less time.

Very few sell center cuttings because of the perceived value of center cuts. The lack of the smooth growth tip makes them less physically attractive at first – but given time! A center cut will produce a fuller plumeria tree in a shorter time.

Soils and Growing Mediums

What Is Soil?

Soil is a living, breathing, natural entity composed of solids, liquids, and gases.

Soil has five major functions:

Provides a habitat for organisms
Recycles waste products
Filters water
Serves as an engineering material
Provides a medium for plumeria growth

Our focus will be on the fifth function. In this role, soil provides structural stability for plumeria and retains and relinquishes water and the nutrients necessary for plumeria growth.

An ideal soil for plant growth contains 50% porespace and 50% solids, with the porespace filled with equal parts air and water. This distribution rarely occurs because porespace varies with soil texture and soil management. For example, tilling increases porespace, while poor drainage and compaction reduce it.

Soil solids are a blend of mineral materials and organic matter. The mineral materials are typically weathered rock of varying sizes called sand, silt, and clay. The organic matter consists of decaying plant and microbial residues. The relative amounts of porespace and mineral and organic matter vary greatly among different soil types. But for plumeria growth, most soil scientists agree that 50% porespace, 45% mineral matter, and 5% organic matter make up an ideal ratio. The distribution of soils and porespace in compacted in poorly drained soil.

Even a small amount of organic matter can have a dramatic effect on the physical, chemical, and biological properties of soil.

¹Brady, N. C. and R. R. Weil. 2004. Elements of the Nature and Properties of Soils, 2nd Edition. Atlanta, GA: Prentice Hall.

The Soil Profile

Most naturally occurring, undisturbed soils have three distinct layers of variable thicknesses. The layers are the topsoil, subsoil, and parent material. Each layer can have two or more sublayers called horizons. Collectively, the horizons make up the soil profile. The predominate parent material varies by location.

Soils’ properties vary with the soil depth. The surface soil, or topsoil layer (O and A horizon in Figure 1–2), usually contains less clay, but more organic matter and air, than the lower soil layers. Topsoil is usually more fertile than the other layers and has the greatest concentration of plant roots.

The subsurface layer (B and C horizon in Figure 1–2), known as subsoil, usually has a higher clay content and lower organic matter content than the topsoil.

Soil properties often limit the depth to which plant roots can penetrate. For example, roots will not grow through an impenetrable layer. That layer may be bedrock (Figure 1–3), compacted soil, or a chemical barrier, such as an acidic (very low) pH. A high water table can also restrict root growth due to poor soil aeration. Few big trees grow in shallow soils because big trees are unable to develop a root system strong enough to prevent them from toppling over. Shallow soils also tend to be more drought-prone because they hold less water and thus dry out faster than deeper soils. Water lost to runoff on shallow soils would instead be absorbed by a deeper soil. In addition, deep soils allow the roots to explore a greater volume, which means the roots can retain more water and plant nutrients.

Soils change in three dimensions. The first dimension is from the top to the bottom of the soil profile. The other two dimensions are north to south and east to west. The practical meaning of this three-dimensional variability is that as you move across a state, a county, or even a field, the soils change.

Five factors of soil formation account for this variation:

Parent material
Biological activity
Climate
Topography
Time

Differences in even one of these factors will result in a different soil type. Soils forming from different parent materials differ. Soils forming from the same parent material in varying climates differ. Soils at the top of a hill differ from soils at the bottom. The top of the hill loses material due to natural erosion; the bottom gains the material from above. Considering the number of possible combinations of these five factors, it is not surprising that more than 450 unique soil series are currently mapped in North Carolina. Globally, more than 20,000 different soil series occur.

Physical Properties of Soil

The physical properties of soil are characteristics that can be seen, felt, or measured. These include color, texture, structure, and water-holding capacity. Such properties usually determine the suitability of soil as a growth medium. Some physical properties, such as texture, are not economically feasible to change on a large scale.

A soil’s fertility, which is a chemical property, is easier to change than the soil’s physical properties.

Color

Organic matter, the soil minerals present, and the drainage conditions all influence soil color. Color alone is not an indicator of soil quality, but color does provide clues about certain conditions. For example, light or pale colors in grainy topsoil are frequently associated with low organic matter content, high sand content, and excessive leaching. Dark soil colors may result from poor drainage or high organic matter content. Shades of red indicate a clay soil is well-aerated, while shades of gray indicate inadequate drainage (Figure 1–4). In well-drained soils of the NC mountains and piedmont, the subsoil colors are often shades of red, brown, and yellow. In poorly drained soils, the subsoil is grayer in color.

Texture

Soil texture, which refers to the proportions of sand, silt, and clay, influences nearly every aspect of soil use and management. Sand is the largest particle (at 2.0 to 0.05 mm), silt is much smaller (0.05 to 0.002 mm), and clay is the smallest (less than 0.002 mm) (Figure 1–5). To compare particle sizes, imagine that a sand particle is the size of a basketball. On that scale, a silt particle would be the size of a marble, and a particle of clay would be a pinpoint. How fine (clayey) or coarse (sandy) a soil is will determine many of the soil’s physical and chemical properties.

Much of a soil particle’s ability to react with water and nutrients is related to the amount of surface area available. When the individual particle size is small, more individual particles will fit in a given space, and thus make more surface area available. Clay, with its tiny particle size and platelike structure, holds water and nutrients effectively, while sand, which has a large chunky structure, does not. In addition to being smaller, clay particles are composed of different minerals than sand and silt, and a clay particle’s structure is more like a stack of paper plates than a grain of sand (Figure 1–6).

Table 1–1. Particle type, number of particles per gram, and the average surface area per gram.

Particle Type	Diameter (mm)	Number of Particles per gram	Specific surface area (cm²/g)
Clay	< 0.002	90,260,853,000	8,000,000
Coarse sand	1.00-0.50	720	23
Fine sand	0.25-0.10	46,000	91
Medium sand	0.50-0.25	5,700	45
Silt	0.05-0.002	5,776,000	454
Very coarse sand	2.00-1.00	90	11
Very fine sand	0.10-0.05	722,000	227

Rocks and Gravel
Rocks and gravel, which are large, coarse materials, can be found in many soils, but they are not considered when determining soil texture. Although some rocks and gravel in the soil will not affect plant nutrient uptake, they can make the soil difficult to dig. If the garden is mostly rocks or gravel, the soil will have a reduced water- and nutrient-holding capacity, and will be unfit for growing plants. In such a situation, it may be easiest to install raised beds and import soil.

The relative proportions of sand, silt, and clay determine a soil’s textural class (Figure 1–7). For example, a soil that is 12% sand, 55% clay, and 33% silt is in the clay textural class. Soil texture is a permanent feature, not easily changed by human activity. Consider a typical mineral soil that is 6 inches deep on 1 acre. That soil weighs about 2 million pounds. To change the sand content just 1% would require adding 20,000 pounds (or 10 tons) of sand. A 1% change in sand content would have minimal effect. A significant effect might require a 10% change, which would mean adding 100 tons of sand.

Adding organic matter is a more economically feasible alternative for improving soil. Adding organic matter does not change a soil’s texture—the percentage of sand, silt, and clay in the soil—but adding organic matter will alter soil structure by increasing the porespace and improving drainage. Gardeners can be successful with any soil texture, as long as they know the attributes and limitations of that soil.

Typically, laboratory procedures are used to determine the soil texture. It is possible, however, to use the procedure outlined in Figure 1–8 to determine the textural class by the “feel” method. It takes practice and calibration, but it can provide a reasonable estimate of the soil texture.

Sandy or Coarsely Textured Soils (Figure 1–9)

Low in organic matter content and native fertility.
Rapidly permeable and do not hold soil moisture.
Nutrient leaching is a concern, so proper fertilization is a must. Apply smaller amounts of nutrients, and apply them more frequently.
Low in cation exchange and buffer capacities.
Well-suited for road foundations and building sites.
Feel gritty.

Loamy or Medium-Textured Soils (Figure 1–10)

Contains more organic matter.
Permit slower movement of water and are better able to retain moisture and nutrients.
Are generally more fertile.
Have higher cation exchange and buffer capacities.
Feel crumbly.

Clayey or Finely Textured Soils (Figure 1–11)

Higher nutrient-holding capacity.
Higher available water-holding capacity.
Finely textured soils exhibit properties that are somewhat difficult to manage or overcome.
Often too sticky when wet and too hard when dry to cultivate.
May have shrink-and-swell characteristics that affect construction uses.
Feel slippery.

How Do Soil Types Affect Gardeners?
Compaction. Compaction occurs when pressure is applied to soil particles and the air and water are pushed out of the porespaces. Large, cubic sand particles are not easily compacted. Clay particles, small and platelike, are easily aligned and can compact, especially when wet. Compaction inhibits the movement of water, gases (air), and roots. Compacted soils have less infiltration, greater runoff, a higher risk of erosion, and more restricted root growth than soils without compaction. Water drains slowly, which may increase the likelihood of plant root diseases.
Erosion. Sand particles are heavy, so they are not easily picked up and moved by water or wind. Clay particles are sticky, so they are not easily moved. Silty loam particles are light and not sticky, so erosive forces easily move them. Eroded soils are usually harder to till and have lower productivity than soils without erosion. The main causes of soil erosion in North Carolina are insufficient vegetative or mulch cover, and improper equipment and methods used to prepare and till the soil (Figure 1–12).
Soil erosion can be minimized by following a few preventive measures:
Choose plants suited to the soil so they establish well.
Mulch the surface each year with organic materials 1 inch to 3 inches deep.
Adequately fertilize to promote vigorous, but not excessive, plant growth.
Create a water diversion, such as a grass waterway, to capture and slow water movement.
Align rows to follow the land’s contour so that water flowing downhill is slowed.
Use proper tillage methods, such as not tilling when the soil is overly wet and not overtilling.
Plant a winter cover crop.
Consider installing rain gardens to capture sediment and runoff.
Surface Area. The most active part of a soil particle is its surface area. A particle’s surface is where nutrient exchange takes place. Sand particles have a small surface area relative to their mass, meaning they do not hold onto nutrients well. Clay particles have a large surface area relative to their mass, so a small amount of clay can add a significant amount of surface area to a soil, increasing the nutrient-holding capacity.

Structure

Soil structure refers to the grouping of individual soil particles into larger pieces called peds or aggregates. The structure of topsoil is usually granular and resembles chocolate cookie crumbs (Figure 1–13). Good granular structure allows rapid movement of air and water within the soil. Poor granular structure decreases movement of air and water. Good soil structure allows for extensive root development; poor structure can limit root growth. Supplying an adequate amount of organic matter and working the soil only when it is not excessively wet promotes good topsoil structure.

Water-Holding Capacity

Water enters the soil from precipitation or irrigation. It exits by draining from the soil, evaporating from the surface, and through transpiration from plant leaves. Water-holding capacity—the retention of water moving through soil—depends on differences in soil porespace. Ideal soils are half porespace with equal amounts of air and water filling the pores. Too much air means plants will wilt. Too much water means reduced plant vigor and susceptibility to root rot, which occurs due to anaerobic conditions.

Soils differ in the number of large (macro), medium (meso), and small (micro) pores. Macropores, which are more common in sandy soils, take up water more quickly and drain faster than meso- and micropores. This rapid draining from macropores is called “gravitational water” because the weaker forces of adhesion and cohesion in macropores cannot overcome gravity’s pull. Within 24 hours after a saturating rain, gravitational water reaches the lower soil horizons, and the soil is at field capacity: the meso- and micropores are still full of water because their adhesive and cohesive forces are stronger than gravity. Water in the mesopores is available to plants. But when the mesopores lose water as the soil dries through plant uptake and transpiration, soil moisture reaches the permanent wilting point. At the permanent wilting point, micropores are still full of water, but this water is so tightly held that it is not plant-available. Note that plants may wilt before the permanent wilting point if the plant transpires water through the leaves faster than it can take water up from the soil through its roots. This is why plants may wilt on hot days and then recover once the sun goes down and why plants can balance uptake with transpiration (Figure 1–14).

How to Remediate Compaction

Compaction is a likely problem if there has been recent construction or other traffic over the area. Deep cultivation, which is mixing the top 6 inches to 2 feet of soil with a tiller, disk, or hand tools, may be needed to loosen the soil. Incorporation of organic matter during deep cultivation can help to rehabilitate soil structure by creating aggregates and both macropores (for drainage) and mesopores (for plant-available water). Digging or cultivating soil when it is wet or excessively dry can destroy structure.

Be wary of quick fixes, such as starting over with a truckload of topsoil. Unfortunately, there are no standards on material sold as “topsoil.” New problems may be brought on site, such as weed seeds and disease organisms. Adding new topsoil to existing soil may also create drainage problems when water moves through the purchased topsoil and reaches the compacted layer. The water can pool and create unfavorable conditions for root growth.

Clay soils, which tend to hold excessive amounts of water and become compacted easily, present some tricky problems. Common mistakes are adding sand or peat moss to improve drainage. Adding sand to clay will reduce soil structure, lowering porespace. Adding peat moss will increase the clay soil’s high moisture-holding capacity. The best advice is to add smaller amounts of organic matter consistently every year, minimize compaction, and let soil biology naturally improve the structure over time.

Organic Matter

Organic matter consists of the remains of plants and animals and gives soil a gray to very-dark-brown color. Organic matter is home to many soil organisms.

Earthworms, insects, bacteria, fungi, and animals use organic matter as food, breaking it down to obtain energy and essential nutrients. Humus is the portion of organic matter that remains after most decomposition has taken place (Figure 1–16).

When organic matter decomposes in the soil, carbon dioxide is released and replaces some of the oxygen in soil pores. Carbon dioxide is dissolved by water in soil to form a weak acid. This solution reacts with soil minerals to release nutrients that can be taken up by plants. The digested and decomposing organic matter also helps develop good air-water relationships. In sandy soil, organic material occupies some of the space between the sand grains. This binds them together and increases water-holding capacity. In a finely textured or clay soil, organic material creates aggregates of soil particles. This allows water to move more rapidly around soil particles.

The amount of organic matter in the soil depends primarily on rainfall, air temperature, the kinds of plants that have been growing in a soil, management practices, soil temperature, and drainage. Soils that are tilled frequently are usually low in organic matter because tilling decreases residue particle size and increases the amount of air in the soil, increasing the rate of organic matter decomposition. Poorly drained soils tend to have a high percentage of organic matter because low oxygen levels limit decomposition organisms. To build organic matter in garden soil, till in compost when the garden is first created, but do not till in subsequent years. Instead, apply thin layers (1 inch to 3 inches), of organic mulch or compost to the soil surface each year (Figure 1–17). This material will break down, and the organic matter levels in the soil will gradually increase.

Improving the Soil

Good aeration and drainage, as well as the ability to hold adequate moisture and nutrients, are key components of an ideal soil environment. Although there is no cookbook recipe for creating this ideal environment, these are some of the most important strategies for improving soil quality:

Minimize soil compaction (do not walk on garden beds or work wet soil) (Figure 1–18).
Reduce drainage problems.
Decrease erosion.
Plant a cover crop (Figure 1–19).
Incorporate organic matter.
Provide a 1- to 3-inch layer of organic mulch on the soil’s surface.

Organic amendments can improve soils that suffer from high compaction, poor drainage, and erosion. Materials such as compost, manures, and pine bark are more effective and economical than vermiculite, peat moss, sand, topsoil, or perlite. Table 1–2 reviews the amounts of organic material to be added to soil per 100 square feet. When working in small areas, a general rule of thumb is to incorporate a 3- to 6-inch layer of organic material into the soil. The organic matter must be decomposed before plants can use the nutrients. The rate of decomposition of organic matter by soil organisms is affected by moisture, temperature, particle size, the carbon-to-nitrogen ratio, and nitrogen availability. The proper balance of carbon and nitrogen is needed for rapid decomposition, as are warm temperatures and adequate moisture. When using straw, leaves, or sawdust (which are high in carbon), add nitrogen fertilizer while the material is decomposing. Soil microbes use nitrogen during decomposition and may deprive plants, resulting in slow or stunted plant growth. Incorporating organic matter some months before planting the garden allows the material time to decompose and have plant-available nutrients in place for good plant growth.

Table 1–2. Organic Materials and Their Application Rates

Organic Material	Amount to Be Added per 100 Square Feet
Compost	10–20 cubic feet
Corncobs	50 pounds (2 bushels)
Hay	60 pounds (1 bale)
Leaves	75 pounds (3–4 bushels)
Sawdust	50 pounds (2 bushels)
Straw	60 pounds (1 bale)
Wood chips	50 pounds (2 bushels)

Incorporating Soil Amendments

Conditioning soil requires increasing organic matter content to 25% by volume. Incorporating a minimum of 2 inches of material into the top 6 inches of soil will create approximately 8 inches of amended soil. These additions raise the planting bed, improving drainage and making plants more visible. Incorporating more than 50% organic matter may negatively affect plant growth. Be careful when using organic material, making certain that it is fully composted and not merely aged. Microbes attracted to partially decomposed materials will compete with plants for nutrients, especially nitrogen and sulfur, resulting in nutrient deficiencies and poor plant growth.

The best organic matter amendments for clay soils are pine bark (less than 1/2 inch in diameter) and composted leaf mold. The following amendments are not recommended because they do not adequately improve the physical properties of clay soil: peat moss, sand, hardwood bark, wood chips, and pine straw.

For sandy soils, organic matter amendments, such as pine bark or compost, will improve water retention.

Figure 1–19. A cover crop of white rye grass was planted in this annual flower bed. It is being turned under to add nutrients to the soil before planting.

Chemical Properties of Soil

There are strong relationships between soil physical properties and soil chemical properties. For example, surface area is directly related to chemical reactivity.

Cation Exchange Capacity (CEC)

The negative ends of two magnets repel each other. The negative end of one magnet attracts the positive end of another magnet. This same principle affects the retention of plant nutrients in soil. Some plant nutrients are cations, which have a positive charge, and some are anions, which have a negative charge. Just like the opposite poles on magnets, cations will be attracted to anions.

Soil particles are similar to a magnet, attracting and retaining oppositely charged ions and holding them against the downward movement of water through the soil profile. The nutrients held by the soil in this manner are called “exchangeable cations” and can be displaced or exchanged only by other cations that take their place. Thus, the negative charge on a soil is called the cation exchange capacity (CEC). Soils with high CEC not only hold more nutrients, they are better able to buffer or avoid rapid changes in the soil solution levels of these nutrients. A soil test will tell you the CEC number of your soil. Soils high in clay, silt, or organic matter will have a CEC number of 10 or greater, and no remediation is needed. Sandy soils will have a CEC number between 1 and 5. Adding organic matter to these soils will help increase the CEC.

Too Much of a Good Thing: Nitrogen Leaching

Soil testing provides valuable information on pH and plant-available nutrients. Test your soil before planting and every two to three years thereafter. Inexpensive soil test kits are unreliable. To accurately determine your soil characteristics and the proper amount of lime and fertilizer to apply, contact the NC Department of Agriculture and Consumer Services (NCDA&CS). The accuracy of these reports, however, depends on the quality of the sample submitted.

Soil Testing Just like magnets, negative charges repel negative charges. Soils with high CEC tend not to hold anions. As a result, water moving through the soil profile will leach negatively charged nutrients, such as chloride, nitrate, and sulfate out of the root zone. This leaching can result in contamination of groundwater, streams, and lakes or have other environmental implications (Figure 1–20). Excess fertilizer becomes a contaminant and can have adverse effects on human health. The U.S. Environmental Protection Agency has set standards for nutrients in groundwater used for drinking water. This is one of many reasons that appropriate levels of fertilization are essential.

Tips for Collecting a Good Soil Sample

Collect samples with stainless steel or chrome-plated tools. Using brass, bronze, or galvanized materials could contaminate the sample.
The bucket in which material is collected should be made of plastic.
Make sure the collection bucket is clean because even small amounts of residual lime or fertilizer can affect the test results.
Avoid taking samples from areas that are obviously different from the norm, such as wet spots, compost piles, animal urine spots, and brush piles, or from under eaves or sites where trash has been burned.
Remove large pieces of organic material, such as roots, stalks, and leaves, from the sample.
For gardens, new lawns, and other cultivated areas, sample to the depth the soil has been, or will be, tilled. For established lawns, collect the sample 2 to 4 inches deep. For trees and shrubs, take a sample to a depth of 6 inches near the plant’s drip line. Even if the soil looks the same, take separate samples for flower beds, vegetable gardens, fruit orchards, shrub borders, and lawn areas.
If using a trowel or spade, dig a hole, then take a slice of soil down one side. Repeat this procedure in five to eight spots for each area to be tested. Mix these cores together to obtain one composite sample. If the soil is very wet, it could be more difficult to mix, but do not attempt to heat the soil to dry it (Figure 1–21).
Place about a pint of the composite sample for each area sampled in a soil testing box and label with a return address on the side of the box. Make up a code that will be easy to remember, such as “flawn” for front lawn, “byard” for back yard, or “veg” for vegetable garden. Any combination of letters and numbers can be used. Make notes about where the samples came from so that when you receive the results, you can easily Identify how to treat the areas differently based on the results.
Do not tape the boxes in any way. The lids are removed before the boxes go in the soil lab ovens, and tape makes this process difficult. Do not put the soil in a plastic bag before placing it in the box as doing so will prevent proper drying in the lab oven.

Fill out the soil test report sheet, giving as much information as possible. The required items are name, address, county, sample codes, and the crops planned. Reports are sent by mail only if there is a special request submitted to the lab. Otherwise, provide an email address on the form to receive notification that the report is complete and online. Farmers also use the form, so some of the information requested may not apply to gardeners (pounds of lime per acre, for example). Forms and boxes are available from the NCDA & CS or any county Cooperative Extension center.

Learn more about collecting soil samples in SoilFacts: Careful Soil Sampling—The Key to Reliable Soil Test Information (NC Cooperative Extension publication number AG-439-30). For detailed information about the soil test results, refer to NCDA&CS Agronomic Division’s Understanding the Soil Test Report.

How to Use a Soil Test Report

Fertilizing trees and shrubs in a landscape should be based on the amount of rainfall, soil type, the plant’s age, the amount of current growth, and desired future growth. Over application of fertilizer to home landscapes wastes money, contributes to pollution in our rivers, streams, lakes and estuaries, and may damage or kill desired plants. In addition, excess fertilizer can increase the likelihood of disease problems, lead to weak growth, attract pests, and increase the amount of pruning to keep mature plants within appropriate boundaries. A soil test report provides accurate guidance for applying fertilizer.

Example Soil Test Reports

Depending on the crop indicated when the soil sample was submitted, the soil test report provides results in one of two ways:

Home garden scale: Recommendations for pounds of lime and a rate and grade of fertilizer per 1,000 square feet (for example, an area 50 feet by 20 feet or 10 feet by 100 feet).
Farm/Forest scale: Recommendations for tons of lime and a rate and grade of fertilizer per acre.

At the home gardener scale:

Measure the area to be limed or fertilized.
Multiply the length by the width to determine the number of square feet.
Divide by 1,000 to obtain the number of units to be treated.
Multiply the number of units by the pounds of material to treat 1,000 square feet. This calculation will give the amount of fertilizer and lime needed (Figure 1–23).

Example 1:
If the area is 500 feet by 20 feet, and the suggested lime or fertilizer treatment is 30 pounds per 1,000 square feet:

500 × 20 = 10,000 square feet
Divide 10,000 by 1,000 = 10 units
Multiply 30 pounds times 10 units = 300 pounds of material (fertilizer or lime) per 10,000 square feet

Example 2:
If the area is 10 feet by 15 feet, and the suggested lime or fertilizer rate is 10 pounds per 1,000 square feet:

10 × 15 = 150 square feet
Divide 150 by 1,000 = 0.15
Multiply 10 pounds times 0.15 units = 1.5 pounds of material per 150 square feet

Or, look at fertilizer/lime calculations as ratios:

If 5 pounds of fertilizer are applied per 1,000 square feet, how many pounds should be applied to 150 square feet (using the garden size in Example 2)?< /p>
5 lb/1,000 sq ft = X lb/150 sq ft
5 lb × 150 sq ft /1,000 sq ft = X lb
750/1,000 = .75 lb
Example soil test reports and their recommended fertilizer applications can be found in Figure 1–24, Figure 1–25, Figure 1–26, and Figure 1–27.

Soil pH

Soil pH is a measure of the soil’s relative acidity or basicity. The pH scale ranges from 0 to 14. A pH of 7 is a neutral state, representing the value found in pure water. Values above 7.0 are basic, while values below 7.0 are acidic. The pH scale is logarithmic, meaning each unit has a 10-fold increase of acidity or basicity. Thus, compared to a pH of 7.0, a pH of 6.0 is ten times more acidic, and a pH of 5.0 is 100 times more acidic.

Nutrient Availability and pH

The optimum pH for a plant varies with organic matter content and plant type. Plant nutrient availability is strongly tied to the pH in the soil solution (Figure 1–28). Decreasing soil pH directly increases the solubility of the plant nutrients manganese (Mn), zinc (Zn), copper (Cu), and iron (Fe). Acidic soils make these nutrients more available. At pH values less than about 5.5, toxic levels of Mn, Zn, or aluminum (Al), a non-nutrient element very common in our southern soils, may be released. The impact of pH on nutrient availability is very important—both for maximum plant availability and to avoid potentially toxic levels at very low or very high pH.

The optimal pH for growth differs among plants. For example, regardless of organic matter content, azaleas and blueberries are well-suited for a soil pH of about 5.0. In contrast, asparagus can tolerate a basic soil with a pH up to 8.0. A soil pH of 6.5 to 7.0 is often considered “ideal” for most plants, but a little research can help you identify the proper pH for the plants you wish to grow. After obtaining a soil test report, you can take measures to adjust soil pH or select plants that will thrive at the current pH. Extreme pH measures of 4.0 (acidic) or 10.0 (basic) will support little plant life and are very difficult to modify.

Adjusting pH

If the soil pH is too basic for the desired plant, incorporating an acidic soil amendment such as pine bark or compost, or applying elemental sulfur, will lower soil pH. Apply sulfur with caution; too much can harm plants.

If the soil pH is too acidic, apply lime to raise the soil pH. There are two general classes of liming materials: calcitic (without magnesium) and dolomitic (with magnesium). Calcitic lime is composed of calcium carbonate (CaCO₃) and can be used on soils high in magnesium. Dolomitic lime is a mixture of calcium and magnesium carbonates (CaCO₃ and MgCO₃), which is the preferred liming material for soils low in magnesium.

Knowing the soil type or even the current pH is not enough to determine the amount of lime needed. The texture of the soil, organic matter content, crop to be grown, target pH, level of soil acidity, CEC, type and amount of clay, and the current pH are all factors to consider in adjusting pH. Soils low in organic matter or high in sand content require less lime to change the pH than clay soils or those with high organic matter.

Lime is heavily regulated in North Carolina. Lime must be labeled with a guarantee of percent calcium and magnesium. The percent of calcium carbonate equivalent also must be included on the label, as well as the pounds of material that equal 1 ton of standard lime (Figure 1–29). Each type of lime must meet a screening requirement for particle size. Lime pellets are formed from lime that has been finely ground. The pelleted product is less dusty and easier to apply, but is slower to react with the soil.

Lime moves slowly in the soil and neutralizes acidity only in the area where it is applied. To be effective, it should be spread and thoroughly incorporated. It takes several months for lime to react in the soil, which is why it is good to soil test and plan for proper soil pH management. For established lawns, gardens, and ornamentals that require lime, apply the recommended amount up to 50 pounds of lime per 1,000 square feet in one application to the soil’s surface. For recommended rates over 50 pounds, wait several months to make a repeat application to avoid a surface buildup of lime. For new plantings where the area will be tilled, apply the entire recommended amount at one time.

Learn more in SoilFacts: Soil Acidity and Liming: Basic Information for Farmers and Gardeners.

Plant Nutrition and Fertilization

Many people confuse plant nutrition with fertilization. Plant nutrition refers to the needs of the plant and how a plant uses the basic chemical elements. Fertilization is the term used when these elements are supplied to the soil as amendments. Adding fertilizer during unfavorable growing conditions will not enhance plant growth and may actually harm or kill plants.

To complete their life cycle, plants need 17 essential nutrients, each in varying amounts (Table 1–3). Of these nutrients, three are found in air and water: carbon (C), hydrogen (H), and oxygen (O). Combined, C, H, and O account for about 94% of a plant’s weight. The other 6% of a plant’s weight includes the remaining 14 nutrients, all of which must come from the soil. Of these, nitrogen (N), phosphorus (P), and potassium (K), the primary macronutrients, are the most needed. Magnesium (Mg), calcium (Ca), and sulfur (S), the secondary macronutrients, are next in the amount needed. The eight other elements—boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc—are called micronutrients because they are needed in much smaller amounts than the macronutrients.

Table 1–3. Relative Amounts (out of 100) of the Essential Nutrients Required by Most Plants

Primary Nutrients
Carbon (C)	45
Oxygen (O)	45
Hydrogen (H)	6
Nitrogen (N)	1.5
Potassium (K)	1
Phosphorus (P)	0.2
Secondary Nutrients
Calcium (Ca)	0.5
Magnesium (Mg)	0.2
Sulfur (S)	0.1
Micronutrients
Iron (Fe)	0.01
Chlorine (Cl)	0.01
Manganese (Mn)	0.005
Boron (B)	0.002
Zinc (Zn)	0.002
Copper (Cu)	0.0006
Molybdenum (Mo)	0.00001
Amounts unknown for Nickel (Ni) and Cobalt (Co)

Soil Nutrients

For a plant to absorb an element, it must be in a chemical form used by the plant and dissolved in the soil water. In addition to those nutrients already dissolved in soil water, nutrients can be present in the soil in these forms:

Undissolved or granular form, as from newly applied fertilizer
Chemicals bound to soil particles
The chemical structure of soil organic matter released by microbial decomposition

Undissolved or granular nutrients, and those that are chemically bound to soil particles, are not immediately useful, although they have the potential to benefit the plant. For many plant nutrients, the soil acts as a bank. Withdrawals are made from the soil solution, much as you would withdraw money from a checking account. The undissolved pool of soil nutrients is like a savings account. When checking funds are low, transfers are made from the savings account to the checking account. When a checking account is flush with money, some can be moved to savings for long-term retention. In the same way, for many plant nutrients, when the soil solution has excess nutrients, some bind to the soil to become temporarily unavailable, and some react with other chemical elements to form insoluble minerals, which can dissolve again later.

Several factors improve a plant’s ability to use nutrients:

Type of soil: The more clay and organic matter a soil has, the higher its CEC will be, and the more cationic (positively charged) nutrients it will retain.
Soil pH: The pH affects how tightly nutrients are bound to soil particles. If the soil pH is extremely high (basic) or very low (acidic), many nutrients become inaccessible to the plant because they are no longer dissolved in the soil water.
Types of nutrients in the soil: Some nutrients affect the availability of other nutrients. In fact, an apparent deficiency of one nutrient may actually be caused by a large amount of another.
Amount of soil water: Too much rain leaches nutrients from the soil. If there is too little water, the nutrients cannot dissolve and move into the plant.
Anything that affects the plant’s growth: If growing conditions are good, a plant will absorb nutrients from the soil. If the plant experiences extremes in temperature, incorrect light levels, or waterlogged or compacted soil, it will have a limited ability to absorb nutrients. Also, plants in dormant stages absorb few nutrients.

The presence or absence of nutrients can cause outward symptoms to appear on the plant. Table 1–4 reviews the essential nutrients for plant growth and symptoms that may appear if a plant is suffering a deficency or an excess of that nutrient.

Fertilizers

Fertilizers provide some elements that might be lacking in the soil and stimulate healthy, vigorous growth. How much and when to apply fertilizers should be based on observing plant performance, a reliable soil test, and an understanding of the factors that affect growth: light, water, temperature, pests, and nutrition. Simply applying fertilizer because a plant is not growing adequately will not solve many plant problems (insects, disease, or poor drainage, for example), and, in fact, excess nitrogen can often increase insect and disease infestation.

All fertilizers are labeled with three numbers, giving the percentage (by weight) of nitrogen (N), phosphorus (P), and potassium (K). This is referred to as the fertilizer grade.

A 100-pound bag of fertilizer labeled 0-20-10 has 0 pounds of N, 20 pounds of P (reported as P₂O₅), 10 pounds of K (reported as K₂O), and 70 pounds of filler. Filler is added to make the fertilizer easier to spread and to reduce the likelihood of burning plants with too much fertilizer (the fertilizer salts can pull water out of the plant). A fertilizer may also contain secondary macronutrients or micronutrients not listed on the label because the manufacturer does not want to guarantee their exact amounts.

Fertilizers can be divided into two broad categories: natural and synthetic.

Natural fertilizers are commonly misnamed “organic.” “Natural fertilizers” is a more accurate description because these materials can be both complex chemical substances containing carbon (organic materials) or inorganic ores, such as rock phosphate, which are mined. Natural fertilizers containing organic materials include manures and composts, animal byproducts (such as bone meal, blood meal, feather meal), and seed meals. Natural fertilizers that are inorganic ores include potassium and lime.

Natural fertilizers typically release nutrients at a slower rate and over a longer period than synthetic fertilizers because microorganisms are involved in a breakdown and release cycle called mineralization. Moisture, temperature, and the microbial species and populations in the soil affect mineralization. Some water-soluble natural fertilizers, such as fish emulsion, are available when rapid nutrient delivery is desired.

When using natural fertilizers, it is helpful to incorporate them and provide adequate moisture for active microbial populations. When packaged as fertilizers, natural fertilizers will have the nutrient analysis stated on the labels. How much to use varies with the nutrient content of the material. The age of the material is also a factor. Producers are not required by law to state the nutrient content on bulk organic materials, such as compost, manure, and sludges. The source of these materials should be investigated and possible analysis performed at the Plant, Waste, Solution, and Media Lab at the NCDA&CS Agronomic Division before applying large amounts to a home garden.

The age of the natural fertilizers is another important factor. When natural material decays and is rained on, it loses nutrients, especially potassium and, to some extent, nitrogen. Even natural sources of nutrients can be overappled and damage plants. Fresh manures, for example, may injure plants by adding excessive nitrogen or potassium, especially when applied in large quantities.

Natural fertilizers can be expensive if applied in amounts adequate to supply nutrients for good plant growth, but have the added benefit of improving soil structure and plant vigor. When applying natural fertilizers, calculate as closely as possible the amounts of nutrients being supplied. Always err on the low side of application rates, then test the soil and augment as recommended on the soil test report. The nutrient content may need to be supplemented with other natural or synthetic materials to achieve a balanced ration of nutrients.

Synthetic fertilizers are made through industrial processes or mined from deposits in the earth. They are purified, mixed, blended, and altered for easy handling and application. Most are noncarbonaceous chemicals from nonliving sources and are usually cheaper than natural fertilizers. In general, nutrients are more rapidly available to plants because they are more water-soluble or in a form plants can use. The disadvantage is that it may be easier to over apply a synthetic fertilizer than a natural one, which may result in fertilizer burn. In addition, synthetic fertilizers may not support beneficial microbial populations to the same extent as natural fertilizers.

Special-purpose fertilizers are packaged for plants such as camellias, rhododendrons, and azaleas (Figure 1–43). Some of the compounds used in these fertilizers have an acid reaction that can be beneficial to acid-loving plants if the soil they are growing in is naturally neutral or alkaline; however, most soils in North Carolina are usually acidic so these special fertilizers are unnecessary.

Fertilizer spikes or pellets are fertilizers compressed into a form placed in the soil or pots (Figure1–44). They are convenient, but are expensive per unit of fertilizer and do not provide uniform distribution. Nutrients are often concentrated around the spikes or pellets.

Liquid fertilizer can be purchased as a dry powder or as a concentrated liquid (Figure 1–45). Liquid fertilizers are frequently used for houseplants or as a starter solution for transplants. They tend to be more expensive per unit of fertilizer because they are made from refined chemicals.

Foliar fertilizers are dry powders or concentrated liquids that are mixed with water and sprayed on plants (Figure 1–46). Foliar feeding is used when insufficient fertilizer was applied before planting, when a quick growth response is wanted, when micronutrients are locked in the soil, or when the soil is too cold for the plant to use fertilizer in the soil. Foliar-applied nutrients are absorbed and used by the plant quite rapidly. They are expensive per unit of nutrient and only give short-term fertilization (completely absorbed within one to two days). Relying totally on foliar fertilization can be time consuming because the fertilizer must be applied regularly. Improper foliar application of fertilizers can also lead to plant tissue burn.

Learn more about fertilizer usage and nutrient concentrations in the North Carolina Agricultural Chemicals Manual, Chapter IV – Fertilizer Use.

Fertilizer Terms
Fertilizer analysis: The minimum amount of each element in a fertilizer as stated on the label, such as 16-4-8.
Fertilizer ratio: The relative proportion of N, P₂O₅, and K₂O. The ratios of 16-4-8 and 8-2-4 are both 4:1:2, which means 4 parts nitrogen to 1 part phosphorus to 2 parts potassium.
Balanced fertilizer: A fertilizer containing equal parts of each major element, such as 10-10-10.
Complete fertilizer: A fertilizer containing nitrogen, phosphorus, and potassium. Examples of commonly used fertilizers are 10-10-10, 16-4-8, and 12-4-8.
Incomplete fertilizer: A fertilizer missing one or two of the macronutrients, such as 0-20-0.
Weed and feed fertilizers: A combination of fertilizer and herbicide. They are often used on lawns to prevent certain weeds from germinating, or to kill existing broadleaf weeds.
High analysis: A fertilizer containing 30% or more active nutrients, such as ammonium nitrate 33-0-0. The cost per bag is usually more, but the cost per pound of nutrient is less, lowering the cost for fertilizing a given area.

Incomplete fertilizers can be used separately or combined to supply the needed nutrients, often at a reduced cost compared to using a complete fertilizer. For example, gardeners who have a soil with sufficient P and K can save money by applying a nitrogen-only fertilizer, such as ammonium nitrate (34-0-0). If a soil test indicates N and K are needed, but not P, use an appropriate amount of ammonium nitrate and muriate of potash (0-0-60), a naturally occurring material composed almost entirely of potassium, processed to remove impurities and concentrate the product. If a soil needs only P, use triple super phosphate (0-46-0), or for an organic nutrient source apply bone meal (approximately 3-15-0; note that this will add some N) or compost.

Regardless of the fertilizers used, be aware that excess fertilizer can damage plants and move into our stormwater systems, which can cause serious environmental problems.

Plant Nutrients and the Environment

Fertilizer misuse causes environmental and water quality issues. Nitrogen fertilizers, for instance, break down into ammonium and nitrate. The nitrate form of N, while essential for plant growth, is highly mobile and can move through the soil after rainfall or irrigation and contaminate drinking water supplies. Phosphorus holds tightly to soil particles and does not leach through the soil, but affects water quality through runoff and soil erosion. Excess nitrogen and phosphorus are associated with algal blooms (heavy growth of aquatic plants) and limited oxygen, and cause fish kills in lakes, bays, and nonflowing water bodies.

There are several ways to reduce fertilizers’ impacts on water quality:

Apply only materials that are recommended based on results of a soil test. If possible, use slow-release fertilizers and incorporate into the soil. Avoid applying excess nitrogen and phosphorus fertilizer.
Calibrate fertilizer spreaders properly and clean spreaders over the lawn area instead of a hard surface.
Keep the amount of hard surfaces in a landscape to a minimum. When installing a new sidewalk or patio, consider using gravel, porous concrete, stepping-stones, wood decking, or bricks on a sand base (Figure 1–47).
Avoid applying fertilizer to hard surfaces, such as sidewalks, patios, driveways, and streets. Sweep up material that falls on hard surfaces.
Maximize water absorption by aerating lawns and incorporating organic matter in planting beds and gardens.
Prevent runoff by turning off irrigation when the soil is no longer absorbing water.
Avoid applying fertilizer in natural drainage areas or ditches.
Minimize soil erosion by using ground covers, windbreaks, terraces, and mulches.
Mulch under trees and shrubs to reduce impact of falling water.
Maintain a lawn border around planting areas and plant a grass strip between rows in fruit and vegetable gardens.
Plant cover crops on bare soil, such as barren vegetable gardens.
Use a rain barrel under drains to collect runoff and direct excess runoff from roofs onto grassy areas (Figure 1–48).

When to Apply Fertilizer

Soil type affects the frequency of fertilizer application. Sandy soils require more frequent applications of smaller amounts of nitrogen and potash than do clay soils because these nutrients leach more readily in sandy soils. Other factors that affect application frequency include the plant to be grown, the amount of plant growth desired, the amount of water, and the type and release rate of fertilizer applied.

The best time to apply fertilizer and the most effective method of applying it depend on the type of plants being grown. Leafy vegetables require more nitrogen than root crops. Corn is a heavy nitrogen feeder and may require several small nitrogen applications when actively growing. Most established woody plants perform well without fertilization, or with just one application per year. Young plants may benefit from several light applications of fertilizer per year.

Fertilizer is needed when plants are actively growing, never when they are dormant. Nitrogen application will have its greatest effect three to four weeks after application. Excess or improperly timed nitrogen can delay flowering and fruiting or promote tender new growth vulnerable to frost or freeze damage.

Research has shown it is best to broadcast or incorporate fertilizer uniformly over an area rather than concentrating fertilizer in holes or bands in the soil. The most effective method of fertilizing a large area is with a fertilizer spreader; for home gardens, hand fertilization works fine. For new plantings, incorporate fertilizer into the soil and mix it thoroughly. For established plantings, surface application is appropriate.

When fertilizing from overhead, make certain plant foliage is dry and use a broom to brush fertilizer off the foliage, or water thoroughly after applying fertilizer to remove it from plant leaves to prevent burn spots. It is not necessary to remove mulch when fertilizing; irrigation or rainfall will carry fertilizer to the roots. Fertilization should be reduced or delayed during dry weather because the salts in the fertilizer can burn roots if there is inadequate moisture.

Calibrating a Spreader
Fertilizers are more effective if they are applied at the proper rate and with uniform coverage. To accomplish this, calibrate the spreader, which requires a little labor and math.
The two types of spreaders used to apply fertilizer and lime are drop spreaders (Figure 1–49) and rotary spreaders (Figure 1–50). The amount of fertilizer that is spread depends on the opening setting, the type of fertilizer, and the speed at which the spreader is pushed. The drop spreader has a series of holes at the base that can be adjusted to apply different amounts of material. With the rotary spreader, the fertilizer falls into a rotating plate and is spread by the centrifugal force of the plate spinning. Instructions for calibrating a spreader should be available on the Internet at the home page for the spreader manufacturer.

The Biology of Soil

There is more life below the soil surface than there is above. Soil life consists of burrowing animals, such as moles and earthworms, insects, and other soil creatures that are difficult or impossible to see without a microscope, such as mites, springtails, nematodes, viruses, algae, bacteria, yeast, actinomycetes, fungi, and protozoa. There are about 50 billion microbes in 1 tablespoon of soil. In a typical soil, each gram (what a standard paperclip weighs) likely contains these organisms, listed from largest to smallest:

Nematodes—10 to 5,000
Algae—1,000 to 500,000
Protozoa—1,000 to 500,000
Fungi—5,000 to 1,000,000
Actinomycetes—1,000,000 to 20,000,000
Bacteria—3,000,000 to 500,000,000

Soil-dwellers move through the soil, creating channels that improve aeration and drainage. Nematodes and protozoa swim in the film of water around soil particles and feed on bacteria. Mites eat fungi, and fungi decompose soil organic matter. The microorganisms’ primary role is to break down organic matter to obtain energy. Microorganisms help release essential nutrients and carbon dioxide and perform key roles in nitrogen fixation, the nitrogen and phosphorus cycles, denitrification, immobilization, and mineralization. Microbes must have a constant supply of organic matter, or their numbers will decline. Conditions that favor soil life also promote plant growth.

Unfavorable soil conditions, such as high temperatures, compaction, or oversaturation can injure beneficial soil life. This can lead to a proliferation of disease-causing fungi, bacteria, or viruses. To read more about common soil diseases see chapter 5,“Diseases and Disorders.” Plants that are stressed by disease are often more susceptible to insect damage. More information on insects can be found in chapter 4, “Insects.” To learn more about managing insects and diseases, please see chapter 8, “IPM .”

To promote soil organisms, incorporate organic matter, till as little as possible, minimize soil compaction, maintain favorable soil pH and fertility, and use organic mulch on the soil surface.

MACRONUTRIENTS
Nutrient	Why Nutrient is Needed	Deficiency Symptoms	Excess Symptoms	Comments
Nitrogen (N)	• Responsible for rapid foliage growth and green color • Easily leaches from soil • Mobile in plant, moving to new growth	• Reduced growth (Figure 1–30) • Light-green to yellow foliage (chlorosis) • Reds and purples may intensify with some plants • Reduced lateral breaks • Symptoms appear first on older growth	• Succulent growth; leaves are dark green, thick, and brittle • Poor fruit set • Excess ammonia can induce calcium deficiency	• High N under low light can cause leaf curl • Uptake inhibited by high P levels
Phosphorus (P)	• Promotes root formation and growth • Affects quality of seed, fruit, and flower production • Increased disease resistance • Does not leach from soil readily • Mobile in plant, moving to new growth.	• Reduced growth • Leaves dark-green; purple or red color in older leaves, especially on the underside of the leaf along the veins (Figure 1–31) • Leaf shape may be distorted • Thin stems • Limited root growth	Shows up as micronutrient deficiency of Zn, Fe, or Co	• Rapidly fixed on soil particles • When applied under acid conditions, fixed with Fe, Mn, and Al • High P interferes with micronutrient and N absorption • Used in relatively small amounts when compared to N and K • Availability is lowest in cold soils
Potassium (K)	• Helps plants overcome drought stress • Improves winter hardiness • Increases disease resistance • Improves the rigidity of stalks • Leaches from soil • Mobile in plant	• Reduced growth • Shortened internodes • Margins of older leaves become chlorotic and burned • Necrotic (dead) spots on older leaves (Figure 1–32) • Reduction of lateral breaks and tendency to wilt readily • Poorly developed root systems • Weak stalks	Causes N deficiency and may affect the uptake of other nutrients	• High N/low K favors vegetative growth • Low N/high K promotes reproductive growth (flower, fruit) • Calcium excess impedes uptake of K
Magnesium (Mg)	• Leaches from sandy soil • Mobile in plant	• Reduction in growth • Yellowish, bronze, or reddish color of older leaves, while veins remain green (Figure 1–33) • Leaf margins may curl downward or upward with a puckering effect	• Interferes with Ca uptake • Small necrotic spots in older leaves • Smaller veins in older leaves may turn brown • In advanced stage, young leaves may be spotted	• Mg is commonly deficient in foliage plants because it is leached and not replaced • Epsom salts at a rate of 1 teaspoon per gallon may be used two times a year • Mg can be absorbed by leaves if sprayed in a weak solution • Dolomitic limestone can be applied in outdoor situations to rectify a deficiency
Calcium (Ca)	• Moderately leachable • Limited mobility in plant • Essential for growth of shoot and root tips	• Inhibition of bud growth • Roots can turn black and rot • Young leaves are scalloped and abnormally green • Leaf tips may stick together • Cupping of maturing leaves • Blossom end rot of many fruits (Figure 1–34) • Pits on root vegetables; stem structure is weak • Premature shedding of fruit and buds	• Interferes with Mg absorption • High Ca usually causes high pH	Ca is rarely deficient if the correct pH is maintained
Sulfur (S)	• Leachable • Not mobile • Contributes to odor and taste of some vegetables	• Rarely deficient • General yellowing of the young leaves, then the entire plant (Figure 1–35) • Veins lighter in color than adjoining interveinal area • Roots and stems are small, hard, and woody	Sulfur excess is usually in the form of air pollution	Sulfur excess is difficult to control, but rarely a problem
MICRONUTRIENTS
Nutrient	Why Nutrient is Needed	Deficiency Symptoms	Excess Symptoms	Comments
Iron (Fe)	• Accumulates in the oldest leaves and is relatively immobile • Necessary for the maintenance of chlorophyll	• Interveinal chlorosis primarily on young tissue, which may become white (Figure 1–36) • Fe deficiency may occur even if Fe is in the soil when: soil is high in Ca; soil is poorly drained; soil is oxygen deficient; nematodes attack roots; or soil is high in Mn, pH, or P • Fe should be added in the chelate form; the type of chelate needed depends upon the soil pH • Foliar fertilization will temporarily correct the deficiency • May be deficient in centipede grass where pH and P are high	Rare except on flooded soils
Boron (B)	• Important in enabling photosynthetic transfer • Very immobile in plants	• Failure to set seed • Internal breakdown of fruit or vegetable • Death of apical buds, giving rise to witches’ broom • Failure of root tip to elongate normally • Young leaves become thick, leathery, and chlorotic (Figure 1–37) • Rust-colored cracks and corking on young stems, petioles, and flower stalks (such as heart rot of beets, stern crack of celery) • Breakdown occurs at the base of the youngest shoots	• Tips and edges of leaves exhibit necrotic spots coalescing into a marginal scorch (similar to high-soluble salts) (Figure 1–38) • Oldest leaves are affected first • Can occur in low pH soils • Plants are easily damaged by excess application •Looks like Mg deficiency,green veins on a yellow leaf.
Zinc (Zn)	Needed for enzyme activity	• Young leaves are very small, sometimes missing leaf blades • Short internodes • Distorted or puckered leaf margins • Interveinal chlorosis (Figure 1–39)	• Severe stunting, reddening • Poor germination • Older leaves wilt • Entire leaf is affected by chlorosis; edges and main vein often retain more color • Can be caused by galvanized metal.
Copper (Cu)	Needed for enzyme activity	• New growth small, misshapen, wilted (Figure 1–40) • In some species, young leaves may show interveinal chlorosis while tips of older leaves remain green	• Can occur at low pH • Shows up as Fe deficiency
Manganese (Mn)	Needed for enzyme activity	• Interveinal chlorosis with smallest leaves remaining green, producing a checkered effect (Figure 1–41) • Grey or tan spots usually develop in chlorotic areas • Dead spots may drop out of the leaf • Poor bloom size and color • Induced by excessively high pH	• Reduction in growth, brown spotting on leaves • Shows up as Fe deficiency • Found under strongly acidic conditions
Molybdenum (Mo)	Needed for enzyme activity	• Interveinal chlorosis on older or midstem leaves (Figure 1–42) • Twisted leaves whiptail • Marginal scorching and rolling or cupping of leaves • Nitrogen deficiency symptoms may develop	• Intense yellow or purple color in leaves • Rarely observed
Chlorine (Cl)	Needed for enzyme activity	• Wilted leaves which become bronze, then chlorotic, then die • Club roots	• Salt injury • Leaf burn • May increase succulence
Cobalt (Co)	• Needed by plants recently established • Essential for nitrogen fixation	Little is known about its deficiency symptoms	Little is known about its toxicity symptoms
Nickel (Ni)	• Needed by plants recently established • Essential for seed development	Little is known about its deficiency symptoms	Little is known about its toxicity symptoms

Disease and Disorders

The term plant disease refers to an impairment in the structure or function of a plant that results in observable symptoms. In this chapter the focus will be on infectious diseases—those that result from attack by a fungus, bacterium, nematode, virus, or other organisms. Other disorders can be caused by abiotic (environmental and cultural) factors, such as compacted soil, excess water, nutrient deficiencies, chemical injury, or air pollution. Many of these factors produce symptoms similar to those caused by infectious agents. Some detective work is often necessary to figure out what is wrong with a particular plant. This chapter provides an introduction to the causes of plant diseases, their diagnosis, and the methods used to prevent and control them. For information on particular diseases, refer to the chapters on specific types of plants.

Healthy and Unhealthy Plants

To recognize a plant problem, you must first know what a healthy plant looks like. Although this may seem obvious, some plants have characteristics or habits at certain stages of growth that can be mistaken for symptoms of the disease. For instance, patterns of light and dark colors on foliage can sometimes indicate disease, but color patterns can also be normal variegation in certain varieties. Sunburst honey locust might appear to be suffering from a nutrient deficiency because it has yellow-green leaves, but this coloring is normal for this cultivar. The spore-bearing sori on the underside of a fern frond might be mistaken for insects. The male cones on the tips of arborvitae foliage look somewhat like galls. Leaves on some evergreen trees (such as some hollies and magnolias) drop in the spring as new leaves expand; homeowners new to North Carolina might become concerned if they expect leaves to shed only in the fall. None of these examples are diseases. Instead, all are normal plant structures and responses.

In order to talk about diseases and disorders, we need a set of terms to describe plant abnormalities and pathogen structures.

Symptoms are not unique to a particular disease as a specific symptom can be caused by a variety of pathogens.

*Chlorosis (adj. chlorotic)*: Yellowing of a normally green plant part. If it is more pronounced between veins it is called “interveinal chlorosis.”	*Necrosis (adj.* necrotic)**: Death of plant tissue. A necrotic leaf blotch is pictured. Note that any well-defined dead area of a leaf, stem, or root can be called a “necrotic lesion.”
Example of necrotic (dead) leaf spots with chlorotic (yellow) halos	Shot-hole: Clean-edged, round to oval holes in leaves where necrotic spots have fallen out .
Wilting: Loss of turgor in all or part of a shoot.	Scorch: Necrosis and desiccation of leaf tissue, starting at the margins.
Mosaic or mottle: Patchwork of colors, usually light-green, yellow, or dark-green, against the normal green background color of the leaf.	Ringspot: Chlorotic or necrotic rings or arcs surrounding healthy tissue.
Water-soaking: A dark, “wet” appearance to a spot, best seen by holding the leaf up to a light source.	Flecking or stippling: Numerous very small chlorotic or necrotic points.
Blight: Extensive and rapid death of plant tissue.	Dieback: Death of a branch from the tip down.
Canker: Sharply-defined dead area on a woody plant part.	Example of a canker visible only under the bark.
Root rot: Decay of roots. The exterior portion is easily pulled off the central core of vascular tissue.	Fruit rot: Decay of fruit. May be firm or soft.
Mummy: A dried, shriveled fruit.	Damping-off: Death of seedlings, before or after emergence from the soil.
Malformation: Any deviation from the normal shape of a plant organ.	Leaf galls: Swellings on leafy tissue.
Stem galls: Swellings, usually woody, on stems.	Root galls: Swellings on root tissue.
Gummosis: Exudation of sticky sap. In conifers, this is known as “resinosis.”	Witch’s broom: Abnormal proliferation of shoots on one area of a stem.
Vascular discoloration: Darkening of the plant’s conductive tissue. Visible after cutting along or into the stem.

Specific terms are used to describe the overall patterns of death or discoloration in turf, independent of what the symptoms may be on individual leaves, stolons, and other parts. These are known as stand symptoms. Several of the most important are illustrated below. All photos are courtesy of NC State University.

Spots: Each area of affected turf is less than 4” in diameter.	Patches: Irregularly shaped areas greater than 4” in diameter.
Circle: Perfectly circular areas greater than 4” in diameter.	Rings: Surrounded by healthy turf to the inside and outside of the affected area.
Irregular: No visible pattern.

Here we see the causal organism itself, usually a fungus.

Mycelium: The visible vegetative body of a fungus, made up of threads called hyphae. (sing., hypha).	Gray mold): Fungal surface growth, gray in color.
Powdery mildew: White surface growth on living leaves, stems, flowers, or fruit. With time this can turn gray or develop minute black flecks within.	Downy mildew: Group of diseases characterized by white, bluish, or gray sporulation on the underside of leaves.
*Sclerotium (pl.* sclerotia)**: Hardened brown or black fungal survival structure. May be round or irregular.	Rust: One of a group of important fungal diseases with multiple stages, at least one of which typically produces a dry yellow to orange spores.
Rust (see above). Example of the aecia of quince rust on ornamental pear fruit. Note the tubular white membranes that cover the spore-producing pustules in this species.	Rust (see above). Example of the gelatinous telia of cedar-apple rust.
Fruiting body: Any spore-producing structure of a fungus. Many are small and dark. Some grow on the surface of leaves or stems.	Canker: Fruiting bodies that develop in a canker, below the bark, and break through the surface.
Mushroom: A soft, stalked fungal fruiting body. One genus —Armillaria—is a plant pathogen. Most are mycorrhizal or are secondary decomposers.	Conk: A tough, often shelf-like fungal fruiting body emerging from standing, fallen, or buried wood. Sign of wood decay in progress.
Dodder: A parasitic plant with yellow to orange stringlike stems and inconspicuous flowers.	Slime mold: A group of soil-, litter-, or bark-dwelling organisms, usually unnoticed until the conspicuous spore-producing phase develops.

Abiotic Disorders of Plants

When the cause of a problem is an environmental condition, cultural practice, or chemical exposure, the causal agent is abiotic (nonliving). Disorders caused by abiotic factors are not contagious, but such disorders can severely damage plants. In these cases, it is more appropriate to use the term injury or disorder rather than disease. Most environmental problems are caused by deficiencies or excesses of factors that support life (including soil moisture, light, and temperature). Simple actions such as soil testing, finding out if a plant prefers sun or shade, loosening the edges of the root ball when planting, watering during dry weather, mulching, and knowing when to lime, fertilize, and prune are major factors in preventing many plant problems. Symptoms such as leaf yellowing, poor vigor, and dieback are the plant’s signal something is wrong with its environment.

Moisture

Both excess moisture and lack of moisture can damage plants. Extreme waterlogging results in root death because of reduced oxygen levels in the root zone. More commonly, excess soil moisture is a contributing factor to root disease. Another disorder that sometimes occurs under high moisture conditions is edema, which appears as numerous swollen bumps on the lower side of leaves. These swellings later turn brown and corky. Edema is common on certain thick-leaved herbaceous and woody plants such as geraniums, camellia, and euonymus. At the other extreme, insufficient moisture can result in scorch symptoms on foliage, stunting, leaf yellowing, leaf drop, and abortion of flowers and fruits. Necrosis can occur on the tips, margins, and interveinal regions of leaves, for example, on sycamore and dogwood trees. Under certain circumstances, potting mixes, mulches, or soils can become hydrophobic (water-repellent). Rain and irrigation will not be effective at getting water to the roots once a hydrophobic condition has occurred. Another type of moisture problem is winter burn. Roots cannot extract water from frozen soil, so the foliage of evergreen trees and shrubs can get a scorched appearance when winter winds dry them out.

Plant Nutrition

Excessive fertilization can result in root burn and plant damage from high concentrations of soluble salts. Lower-than-optimum levels of nutrients usually result in diminished growth and a wide variety of foliar symptoms, depending on the nutrients involved. Even when nutrients are present in the soil, they may be unavailable to plants if the soil pH is not in the correct range. One common nutritional problem that can be mistaken for a disease is the blossom end rot of tomatoes and peppers. Flattened, tan-colored dead spots appear on the fruit, around the point where the flower was attached. This often happens on the first cluster produced on a given tomato plant. In peppers, the damage can also appear elsewhere on the fruit. The affected areas may become dark if secondary molds develop in the affected tissue. The cause is a localized calcium deficiency in the developing fruit. It can be brought on by water stress or by low levels of calcium in the soil. High levels of fertilizer salts—especially ammonium nitrogen—can also contribute to the disorder.

Light, Temperature, Wind, and Weather

Some plants require shade. Sensitive plants such as aucuba can show burn on those leaves most exposed to the sun. Fleshy vegetables such as peppers and tomatoes can show sunscald on fruit. If a large tree is removed from a landscape, the sudden increase in sunlight can damage previously shaded plants. Other plants require sunlight. When planted in shade they have spindly growth until they reach adequate light.

Cold can damage plants that are grown out of their area of adaptation or plants exposed to rapid drops in temperature. Tropical indoor plants are prone to injury from low temperatures—both in the home and while in transport. This kind of chilling injury usually shows up as a blackening of plant tissues soon after the exposure.

Perennial and woody plants develop some tolerance to cold as fall and winter progress but lose this hardiness with the onset of spring. In the fall, cold hardiness first occurs in the terminal buds. The last tissues to go dormant are at the base of the main stem. An early freeze in the fall or a late freeze in the spring results in bark splitting or loss in those lower stems. The plant may not show distress until the heat of summer when the damaged stems are unable to move sufficient water to the foliage. Late frosts often damage the flower buds of peaches, cherries, apricots, and strawberries. Frost damage to new conifer needles will uniformly kill all needles of the same age back to the same point.

Dry winds can pull moisture from leaves, resulting in a scorched appearance. Heavy winds can remove leaves and limbs and effectively sandblast plants. Ice storms can result in broken limbs. Hail can punch holes in leaves or knock plants down. In addition, lightning strikes, fire, and high temperatures can damage or even kill a plant.

All of the abiotic plant problems described above occur naturally. Several other abiotic problems are caused by humans. Examples include air pollution, herbicide injury, and mechanical damage (for example, when a lawnmower hits a tree). Other human-caused abiotic problems include roots girdling on plants left too long in a small pot and compacted soil.

All of these abiotic injuries may attract insects and become entry points for diseases.

Plant Pathogens

We can classify diseases according to the symptoms they cause on particular plant parts. For example, there are leaf spots, fruit rots, petal blights, and other diseases named after plant parts. As a general rule, leaf spot diseases are the least serious because the plant can compensate. Exceptions occur when leaves are killed quickly, as with late blight, or when leaves drop off in large numbers, as with black spot of rose or boxwood blight. Canker diseases on woody plants are more serious because entire limbs can sometimes be affected. Root and crown rots are even more serious because a compromised root system will weaken or even kill entire plants. To make matters worse, the soil inhabitants that attack roots tend to persist from year to year. Perhaps the most destructive group of plant diseases are vascular wilts such as Dutch elm disease or fusarium wilts. In these cases, the water-conducting vessels of the plant are impaired, and decline is rapid and irreversible. One of a gardener’s challenges is to identify whether the disease will affect a plant’s long-term health and if not, whether management is necessary.

An alternate way to classify plant diseases is according to their cause. We use the term pathogen to refer to any organism that can cause disease. Some pathogens affect only a single kind (genus) of plants. Others can infect many members of a single plant family, and still, others have an extensive host range and can attack plants across multiple families. Examples of pathogens include fungi, bacteria (including phytoplasmas), nematodes, viruses, and parasitic plants.

Fungi

Fungi are a diverse group of organisms that include everything from mushrooms to molds. In most cases, the fungal “body” consists of fine microscopic threads that grow and branch out through substrates, such as soil, plant parts, foods, or even skin (in the case of the athletes’ foot fungus). There are almost 100,000 described fungal species. Estimates of the total number of fungi on earth range upwards of 5 million. Fungi lack chlorophyll and thus cannot manufacture their own food. Instead they “feed” by using enzymes to break down organic compounds produced by plants and animals.

Although some fungi are plant pathogens, the vast majority are harmless or even beneficial. For example, saprobic (also known as saprophytic) fungi obtain nourishment from dead plants and animals. In the process, they decay wood, leaf litter, and other debris. This is a part of the earth’s nutrient cycle—a beneficial service unless the wood happens to be part of your home! Other important functions of fungi include flavoring some cheeses, causing the bread to rise, fermenting beer and wine, and producing certain antibiotic precursors.

Examples of common fungal foliar diseases are black spots of rose, powdery mildew, downy mildew, brown patch, and oak leaf blister. Botryosphaeria andPhomopsis species are fungi that commonly cause cankers in woody plant parts. More serious canker diseases include chestnut blight and thousand cankers disease of walnut. Pythium, Phytophthora, and Armillaria species are important causes of root rots. Dutch elm disease and fusarium wilt, already mentioned above, are caused by fungi, as are verticillium wilt, laurel wilt, and oak wilt. Abnormal growth incited by fungi can include twisting and curling of leaves, stunting, or galling, as in the case of black knot or cedar-apple rust.

The life of a fungus may include some time on a plant, in the soil, or on plant debris. Survival and growth of the fungus depend on favorable temperatures and moisture levels. Fungi can be spread by one or more of the following: wind, water, insects, soil, or people. A few have more exotic means of transport, such as via birds or on seeds. Figure 5–56 shows the life cycle of the fungus that causes brown rot on peaches.

The microscopic threads that make up the fungal body are called hyphae, a term that comes from the Greek word for “web.” A visible mass of hyphae is called amycelium. At some stage in their development, the hyphae of many fungi group together to produce other visible signs, such as powdery mildew, conks, or mushrooms. Table 5–2 illustrates a number of these fungal signs.

Some fungi, such as Rhizoctonia solani, spread mainly by the growth of hyphae. But most fungi reproduce via spores. Spores are formed either directly on specialized hyphae or within a fruiting body of some kind. Spore shapes and spore-bearing structures are unique to particular species and can be used to identify fungi under a microscope. Fungal spores almost always require free (liquid) water for a period of time before they can germinate. If foliage stays wet for a certain number of hours at a sufficiently warm temperature, spores of fungal pathogens will germinate, forming hyphae that grow into the plant. Spores that land on dry plant tissue may lie there for several days until moisture becomes available. Depending on the particular fungus, entry into plants can be directly through the cuticle, through stomata, or via pruning cuts, leaf scars, or other wounds.

Some fungal spores are thick-walled and can tolerate dry or cold conditions, but some fungi survive these hardships by forming sclerotia. These small, hard bodies survive in plant tissue or in the soil. Examples include the sclerotia of the fungus Sclerotium rolfsii, which resemble radish seeds in size and color, and those of Sclerotinia sclerotiorium which are black, irregular, and look rather like mouse droppings.

Bacteria

Bacteria are microscopic, single-celled organisms with no organized nucleus. They live in incredibly diverse environments where they have many ecological roles. Plant pathogenic bacterial species number in the hundreds (versus thousands for fungi). Because bacteria look a lot alike under the microscope, they are usually identified by isolating them from plant tissue. Then differences in colony characteristics, biochemical properties, and DNA are used to make the identification.

Unlike many fungi, bacteria cannot penetrate plant cuticles. Rather, they enter through wounds (either caused by human activity or by insect feeding) or through natural openings such as lenticels, hydathodes, and stomata. Bacteria can be spread from plant to plant by way of soil, insects, splashing water, infected seeds, or pruning tools. The bacterium that causes fire blight can be spread by bees. Bacteria do not have specialized survival structures, so many will not survive in infected plant debris once it decays. Unfortunately, some bacteria can survive long-term in the soil or in cankers of woody plants.

Bacteria can cause leaf spots, blights, cankers, and wilts, as well as fruit, stem, and crown rots. Many leaf spots caused by bacteria are angular or linear and have straight edges because spots expand easily between but not across leaf veins. They may also have a water-soaked appearance when held up to the light. With some bacterial leaf spots, a yellow halo surrounds the lesion. Bacterial rots often lead to a slimy texture and a foul odor. How much a disease develops and how quickly it spreads depends on temperature, humidity, maturity of the plant tissue, and susceptibility of the plant. Although there can be distinctive characteristics of bacterial disease, it can sometimes be difficult to distinguish bacterial diseases from those caused by fungi. For example, bacterial leaf spot of English ivy looks a lot like anthracnose, and Alternaria leaf spot of zinnia can be mistaken for bacterial leaf spot of that same host.

The bacterium that causes the southern bacterial wilt of tomatoes and several other plants is soilborne. The bacteria enter the roots and multiply in the xylem tissue. As these water-conducting channels become clogged, plants wilt and die.

Phytoplasmas are an unusual group of bacteria that lack cell walls. They inhabit the phloem of plants and have been associated with several plant diseases. The best known of these is aster yellows, a disease that can infect many other host species besides asters. The aster yellows phytoplasma are spread by leafhoppers. The phytoplasma cause symptoms that include yellowing of foliage, the abnormal green color of flower petals, and shoot proliferation. Xylella fastidiosais another unusual sort of bacterium. It causes the bacterial scorch diseases of sycamore and oak, and Pierce’s disease of grapes. While not a phytoplasma, Xylella fastidiosa is likewise spread by leafhoppers.

What’s in a Name?

Some disease names are confusing simply because the names resemble one another. Be careful to explain that sooty mold is a fungal growth on insect honeydew (easily rubbed off), while sooty blotch is a fungal infection of the surface layer of apple fruit. Likewise, slime mold refers to a group of harmless organisms living in mulch or soil, while slime flux is the discharge of a fermenting liquid from trunks of hardwood trees in midsummer.

At other times confusion can arise when a single name is used in different ways. There’s no problem with “black root rot,” a disease of plants such as carrot, pansy, Japanese holly, and many herbaceous perennials, caused by the fungus Thielaviopsis basicola. Drop the middle word, though, and you have “black rot,” a term used for a disease of crucifers caused by the bacterium Xanthomonas, a disease of grape caused by the fungus Phyllosticta, and a disease of sweetpotato caused by the fungus Ceratocystis. Another example, black leg of geranium, is caused by the water mold Pythium, while black leg of crucifers is caused by the fungus Phoma.

The use of scientific names of pathogens can help avoid some of these problems, but sadly there is confusion in the ranks regarding scientific names, too. Some fungi have traditionally borne more than one name, depending on whether the sexual or asexual form is observed. Scientists are in the process of sorting this out, so stay tuned.

Nematodes

Nematodes are tiny roundworms. Some are famous for causing human and animal diseases such as hookworm, river blindness, and heartworm. Others are beneficial, for example, those used to control fungus gnats in greenhouses. Several hundred species of nematodes—all of them microscopic—are parasites of plants. Most of these are soil inhabitants and feed on plant roots. Nematodes can cause economic losses on everything from turfgrass to peach trees. The host range of individual nematode species can be fairly narrow or tremendously wide. Some nematodes remain outside the root while feeding, while others actually enter it. Once inside the root, some types migrate, while others become sedentary at a particular feeding site. All plant-parasitic nematodes have a needlelike mouth structure called a stylet. The stylet is used to puncture plant cells so that the nematode can obtain food or inject substances into the plant. The direct damage caused by nematodes is not only harmful, the damage also can predispose the host to other kinds of diseases.

Nematode damage interferes with root uptake of water and nutrients. This is why the above-ground symptoms resemble those of other stresses. Nematode symptoms include poor growth, small leaves, wilting, and off-color foliage. Examination of the roots may reveal stunted root systems, dark lesions on roots, or galls. The root-knot nematodes (genus Meloidogyne) are the most destructive plant-parasitic nematodes in North Carolina, in part due to their wide host range. They inject growth-regulating substances into root cells that stimulate the formation of galls or knots that are visible to the unaided eye. The size of the gall varies with the host. The adult nematodes themselves remain hidden within the gall. These galls should not be confused with the nitrogen-fixing nodules formed on the roots of legumes or with the normal swellings on the roots of plants such as liriope, mondo grass, and daylily.

The amount of damage caused by nematodes depends on four factors:

1. The particular species of nematodes present

2. The population levels of the nematodes

3. The particular species of plant involved

4. Growing conditions, such as moisture levels and nutrient status

The plant-nematode combination is critical. For example, we worry about the spiral, lesion, and root-knot nematodes on boxwoods. But our major nematode concern for azaleas is the stunt nematode.

All nematodes reproduce by eggs. Juveniles hatch from the eggs and develop into adults after a series of molts. Many nematode species can survive and complete their life cycles on weeds. In addition, many nematode species are able to survive long periods even in the absence of a plant host. Egg masses are an important overwintering stage for root-knot nematodes, and the eggs of cyst nematodes are protected in a sort of shell formed from the dead body of the female that produced the eggs. These cysts are just barely large enough to be visible on the surface of the roots if you look closely. Fortunately, we seldom see problems with cyst nematodes in North Carolina, except on soybeans.

On their own, nematodes can travel horizontally in the soil only inches to a foot or so per year. For long-distance spread, nematodes rely on the movement of soil clinging to boots, tools, or equipment, and on the shipment of transplants. Once introduced into a new site, it may take years for populations to build to the point where plant injury is noticed.

If you suspect that your soil has plantparasitic nematodes, submit a sample to your county’s Extension center or to the NC Department of Agriculture & Consumer Services for testing.

Two important kinds of nematodes do not fit the general pattern described. Foliar nematodes directly enter leaf tissue, where they cause yellowing and then necrosis. As with bacterial leaf spots, these affected areas tend to be limited by the veins in the leaf and so are angular (as for example in butterfly bush) or linear (as in the case of hosta). Foliar nematodes are particularly a problem in greenhouses and nurseries. The pine wilt nematode is destructive to non-native trees in the pine family. The pine wilt nematode lives within the wood of the trees and is transmitted by a type of longhorn beetle. In North Carolina, the greatest problem with pine wilt nematode is on Japanese black pine along the coast.

Viruses

Plant viruses are very small particles of either DNA or RNA wrapped in a protein coat. They can be visualized only with the aid of powerful electron microscopes. Approximately a thousand plant viruses have been described, with more being discovered continually. Viruses enter plant cells and multiply by using the plant’s own enzymes to manufacture more virus particles. Damage to plant cells occurs because normal cellular processes are disrupted.

Viruses are diagnosed by using knowledge of the viruses affecting certain hosts, observing plant symptoms, and conducting laboratory tests. Symptoms of virus infection are extremely diverse. They can include green and yellow mottling or mosaic, ring spots, color break on flowers, and sometimes necrotic spots. With some viruses, vein clearing (veins are lighter than normal) or vein banding (leaf tissue alongside veins is a darker green than the rest) develops. Stunting leaves, flowers, and entire plants is not uncommon. With a few viruses, leaf malformation or shoot proliferation (witch’s broom) can occur.

Care must be taken when interpreting some symptoms. Chimeras—genetic aberrations in chlorophyll production—look at first glance like a virus-induced mosaic. A “shoestring” distortion of tomato leaves can be caused both by Cucumber mosaic virus (CMV) and by exposure to synthetic auxin herbicides. Witches broom in rose can be caused by Rose rosette virus or by exposure to the herbicide glyphosate. Care should also be taken when interpreting virus names. Rose rosette virus infects only roses, but Cucumber mosaic virus has hundreds of hosts.

Viral infections of plants are incurable and also systemic, meaning that the virus occurs throughout the plant. Any plant that is vegetatively propagated from a virus-infected mother plant will also be infected. This includes propagation by division, cuttings, air-layering, tubers, and grafting. On the other hand, relatively few viruses are transmitted by true seed and very few via pollen. A handful of extremely hardy viruses can be “mechanically” transmitted on hands or tools. These include the Tobacco mosaic virus and its relatives, as well as the Hosta virus X. Many viruses are transmitted by arthropods, such as aphids, thrips, whiteflies, leafhoppers, and eriophyid mites. These insects and mites are referred to as vectors of the virus. For example, thrips are the vector of Tomato spotted wilt virus. So-called “soilborne” viruses are actually spread by nematodes and fungi in the soil. Most viruses die quickly outside a living cell, but they can overwinter in perennial or woody plants and in weeds.

Viroids are virus-like particles consisting of RNA but with no outer protein coat. They cause diseases similar to those caused by viruses and are spread mechanically or via propagation.

Rose Rosette Disease

It is not easy to determine whether a rose bush has rose rosette disease (RRD), which is caused by the Rose rosette virus. Symptoms vary among different rose cultivars, and can change as the disease progresses. Excessive (hyper-) thorniness is a sure sign of RRD, but thorniness does not always occur. Abnormal elongation of shoots, with a retention of the juvenile red coloration (Figure 5–64) in the mature leaves, is a strong indicator of RRD, but it can be hard to be sure you are not looking at normal coloration, especially when presented a single cane. Shoot proliferation (witch’s broom) can occur with RRD, but this symptom can also be caused by exposure to low doses of the herbicide glyphosate. A bright yellow mosaic without leaf deformation represents a much less serious disease called rose mosaic. Because laboratory confirmation of RRD is time-consuming, diagnosticians at the PDIC usually rely on an array of symptoms and the presence of the microscopic eriophyid mite vector when making a diagnosis. Familiarize yourself with the Pest News article (Volume 27, number 21, page 10-12) on this disease, but be prepared to say: “I’m not sure. Let me get a second opinion.”

Parasitic Plants

Parasitic plants include dodder, mistletoe, witchweed, and broomrape. Parasitic plants derive nourishment from the host plant’s vascular system. Dodder and mistletoe attach themselves to aboveground portions of a plant, whereas witchweed and broomrape attach themselves to plant roots. Dodder produces twining yellow to orange stems that resemble spaghetti. Witchweed is a serious pest of corn and has been the subject of quarantine efforts over the last several decades. Native to Africa and Asia

Figure 5–56. The life cycle of Monilinia fructicola A. Spores in the wind, B. Spores infect blossom, C. Blossoms killed, D. Canker develops, E. Fruit infected by spores, F. Fruit rots during summer, G. Fruit mummifies, H. Fruit produces spores early spring.

Disease Development

Although we consider pathogens as the causes of plant diseases, the development of a disease is not automatic. It also depends on the plant and the environment. Each species of plant is capable of being infected by only certain pathogens. A plant is considered susceptible when a pathogen can cause infection. If a pathogen cannot infect a plant, even under conditions favorable for disease development, the plant is considered resistant to that pathogen. Plants have varying degrees of resistance, which can change with each plant’s growth stage. For example, brown rot will develop only on maturing fruit, but peach scab develops on younger fruit. The virulence (aggressiveness) of pathogens can also vary. The environment, especially temperature and the presence or absence of water, will determine how much disease develops. By a long tradition, this relationship is depicted as the disease triangle. Because the process requires time—usually days to weeks—the time element is also included in the diagram. In some versions, the influence of a vector or of human activity is depicted as a fourth corner, making it a disease pyramid.

The beauty of the disease triangle is that it provides a framework for disease management strategies. You can grasp it at one or more of the corners. For example, modifying the environment is one method of controlling disease development. The goal is to make the environment unfavorable for the pathogen, favorable for the plant, or both. You can adjust planting dates, change the spacing between plants, provide good drainage, and avoid wetting leaves during irrigation. Using resistant plants is another strategy, based on the next corner of the triangle. Addressing the pathogen can be key, for example, because some diseases occur only during certain well-defined periods of the year.

Figure 5–57. The disease triangle represents the fact that disease occurs only when a pathogen, a susceptible host, and a favorable environment are all present together, and a sufficient period of time has elapsed.

Spread and Survival of Pathogens

Another important consideration in disease control is how pathogens move around and how they survive when there is no host plant available. Some examples were mentioned above in the section on pathogen groups. Fungi, especially in the form of spores, can move via wind, water, insects, and human activity. Some species of fungi are so versatile that they produce different kinds of spores that may disperse in different ways. Bacterial cells are very often water-splashed from diseased to healthy plants. There they may colonize plant surfaces without immediately causing an infection. Working among plants while they are wet is a good way to spread both fungi and bacteria. Viruses often rely on insect or mite vectors for dispersal and for entry into a plant. Nematodes and their eggs move wherever the soil is moved.

It is critical to understand where and how pathogens overwinter. Many pathogens survive in plant parts that remain alive over the winter, such as roots, bulbs, stems, and buds. Soilborne diseases such as southern bacterial wilt survive in the garden soil. Once a given piece of ground is infested with the causal bacterium, known as Ralstonia solanacearum, it will remain infested indefinitely. Tomatoes planted there will succumb to the bacteria as soon as hot weather arrives. On the other hand, the occurrence of the Tomato spotted wilt virus is a game of chance each year, depending on the survival of the virus in weeds and the movement of the thrips vectors. At the furthest extreme are diseases such as downy mildew of cucurbits. This pathogen can overwinter only in warm climates like Florida’s. The spores are blown long distances on wind currents, reaching North Carolina in late May or June each year. The disease can arrive earlier if spores hitchhike a ride on infected transplants.

The Diagnostic Process

Before rushing in with a hasty diagnosis and recommending action to correct a plant problem, we must identify the cause. Some plant diseases are easily recognizable based on a specimen or photograph, but others may be difficult to identify. We recommend a structured diagnostic process. As you work through the steps below, be aware that a definitive diagnosis is not always possible or even necessary. In some cases, you will simply narrow the list of possibilities to the point where an informed management decision can be made.

Step 1: Gather as much information as you can and take notes. You may want to use the clinic sample submission form as a guide. Also think of the “three Ws (where, when, what) and H (how)” of good reporting. Where is the problem occurring? Be sure to confirm that the plant was actually growing in your county. Plants brought from elsewhere could have problems that are uncommon in your area. In what setting is the plant growing, such as in a pot, in the ground, in a raised bed, or on a north-facing slope? When did the problem first occur? Has it progressed quickly or slowly? Has it spread? When were the plants sown or transplanted to their current site? When was the sample collected? What kind of plant is affected? Is just one species, cultivar or variety affected, or are there many affected? What kinds of plants were grown in this location last year? How was the plant managed in terms of water, mulch, compost, fertilizer, lime, irrigation, and pesticides? How was the weather in the weeks before the problem appeared?
Step 2: Observe the specimen or photos from the site or both. First, verify that the plant has been identified correctly. Then look at the entire plant: roots, stems, leaves, flowers, and seedpods (if any exists). Does it seem to be the right size and color for a plant of the reported age? Do you notice any of the other symptoms listed in Table 5–1a – f? If so, do they occur in the upper portion of the plant, the lower portion, or toward the middle? Are the symptoms or signs different on the upper surface of the leaf versus the lower? If there are color changes, are they generalized across the foliage, or are they mainly between or along the veins? If there are leaf spots, what are their size and shape? If the plant appears wilted, was it that way in the garden? Or did wilting occur since the plant was dug or pulled? How does the leaf look when held up to the light? Are any parts of the plant missing? Look for signs of insects or mites. Their damage is sometimes mistaken for disease. Have leaves or flowers dropped off? What is the distribution of affected plants: scattered, grouped, or otherwise distributed? With turf problems, note carefully both the symptoms on the individual grass plants and whether the “stand symptoms” consist of small spots, larger patches, rings, or just scattered plants. See the Turffiles glossary for more information. In all cases, see if there are any signs of the causal organism, such as those listed in Table 5–2. Be aware that many fungi are secondary and grow on plant parts damaged or killed by another pathogen.
Step 3: Compare your observations with the easily recognized diseases and disorders described in Table 5–3a – f and come up with a diagnostic hypothesis. Be aware that some symptoms are unique to particular diseases, whereas other symptoms can be caused by a wide range of factors. Wildly excessive thorn production on roses is a foolproof indicator of the Rose rosette virus, but not every rose-rosette-infected bush shows this symptom. Mosaics (Figure 5–11) are usually the result of a viral infection, as are ring spots (Figure 5–12). The famous exception to this is that African violets will develop ring spots when cold water contacts the leaves. Leaf spots with an angular or linear shape because the spots stop abruptly at the major veins often indicate a bacterial infection, downy mildew, or foliar nematodes. Wilting, on the other hand, can have many causes. See the special section “When Plants are Wilted.”
Step 4: Double-check your diagnosis. Once you have a shortlist of possible causes, look for photos and descriptions in Extension publications or other references you may have on hand or online. Is there anything that can help rule out one or more of the possibilities? Make more observations if needed. With experience, you will be able to confidently identify a number of diseases. If you cannot reach any conclusions, show the sample to an Extension agent or the PDIC.
Step 5: Make recommendations, if possible, based on what you were able to determine from the suggestions presented above and consult available extension publications for recommended ways of managing the problem. Sometimes there is nothing that can be done to alleviate a problem in a home garden situation. In other cases, cultural practices can reduce the impact of the disease this year or in the future. In a few cases, fungicide applications may be worthwhile. Always encourage integrated pest management (IPM) approach. A study of plant pathogens and the disease development and spread (will give you a better understanding of how diseases occur and which management strategies are helpful and when management is useless.

Be especially careful about the following situations:

Vegetables

Necrotic spots or blotches on the leaves of crucifers (including cabbage, collards, and broccoli). These spots may be the result of black rot, caused by the bacterium Xanthomonas campestris. The typical v-shaped lesions are not always present, making diagnosis difficult at times.This disease has a lot of destructive potential.
Wilting of tomato plants in the garden without a visible sign of fungal activity. (See When Plants are Wilted.) Whether the cause is nematodes, southern bacterial wilt, the early stages of southern stem blight, or something else entirely, wilting can have serious long-term implications for the garden.
Leaf spots on tomatoes and peppers. Spots caused by bacteria, fungi, or even Tomato spotted wilt virus can look surprisingly similar. Some are more serious than others, and control measures are quite different.
Large areas of tomato or potato foliage turning gray or gray-green and withering in a short period of time, often accompanied by large rotted spots on tomato fruit. These symptoms can indicate late blight, a very destructive disease that the PDIC helps to monitor. The timing of its appearance in North Carolina varies from year to year.
Stem rots, leaf spots, and blights of cucurbits. Downy mildew, several true fungi, and two kinds of bacteria can cause leaf spotting in cucurbits. In addition, downy mildew is subject to monitoring because it shows up at different times and in different places each year. When stems are involved, the laboratory can help to differentiate between the various possible causes. Note that gummosis (Figure 5–27) on stems is a response to a number of kinds of stress, not just the disease known as “gummy stem blight.”
Anything involving leaf distortion or dwarfing. These symptoms can be caused by viruses, mites, or insects, or by chemical injury.

Fruit and Nut Trees

Fruit and nut trees in the home orchard present particular challenges for diagnosis. Refer anything to the PDIC that does not fit the pattern of one of the diseases described in Table 5–3c.

Other Trees and Woody Ornamentals

Table 5–3d mentions a number of diseases of woody ornamentals. When none of those seems to fit, the PDIC can be of assistance. It is important to get a good sample that includes sufficient roots in soil, plus the right parts of branches and foliage. It normally is not enough to have just detached leaves, or stems that are completely dead.
If dieback symptoms are present, carefully cut away a strip of outer bark from an affected branch. If you find a very clear boundary between live and dead cambium (or inner bark), it is likely a canker disease

Herbaceous Ornamentals

Root and stem rots—For confident diagnosis of root rots in bedding plants, a microscope and selective media are often needed. The results are important because they affect the choice of replacement plants. (See “When Plants are Wilted.”)
Blights—When large areas of foliage die in a short period of time. even when lower stems, roots, rhizomes, and other plant parts look good, then a laboratory diagnosis is helpful.

Important: Problem names can vary, depending on the host plant and the plant part affected.

GENERAL

Problem	Occurs on	Season*	Hallmarks	Cause
Artillery fungus	Leaves, walls, windows, cars	(W, Sp) Su, F	Circular, dark raised specks about one-tenth of an inch across. When scraped off, a persistent stained spot remains.	Spore balls shot from the fungusSphareobolus growing on mulch.
“Dog-vomit” slime mold (Figure 5–48)	Mulch, walls, tree trunks, and other wood surfaces	Su	Yellow frothy masses several in. to a ft. wide, developing a pink crust over dusty dark spores.	Fuligo septica, a harmless organism unrelated to fungi.
Sooty mold	Any plant	Su, F	Black mold on upper surface of leaf is easily wiped off with fingers (Figure 5–69).	Fungi growing on insect honeydew. Not damaging to plants except blocking photosynthesis.
Stinkhorns	Mulched beds	Su, F	Foul-smelling, horn-shaped fungi with dark sticky tops and tan or orange stalks, developing from egg-like structures in the ground.	Several fungi that develop in decaying plant material. (Some differ from the description at left.)

*Time of year encountered in field and garden:. Sp—Spring, Su—Summer, F—Fall, W—Winter.

VEGETABLES

Problem	Occurs on	Season	Hallmarks	Cause
Blossom-end rot	Tomato, pepper	Su	Flattened dead areas on blossom-ends of fruit (Figure 5–52). Tan-colored, becoming dark (Figure 5–54) if secondary fungi invade. In pepper (Figure 5–53), can occur on the sides of the fruit.	Calcium deficiency in developing fruit due to lack of Ca in soil or moisture fluctuations.
Common smut	Sweet corn	Su	Ears or other parts develop whitish galls that fill with dusty black spores.	Ustilago maydis (fungus).
Glyphosate injury	Tomato is very sensitive, but any plant can be affected.	Su, F	In tomato: bright yellow coloration of youngest leaves, often at the base of leaflets. At higher doses plant death occurs.	The drift of spray droplets from the nearby application of glyphosate herbicide.
Powdery mildew	Cucurbits (Figure 5–70), others	Su, F	White to gray fungal growth on upper and/or lower leaf surfaces.	Different fungi, each specific to a group of plants, e.g.,Podosphaera xanthii on cucurbits.
Root-knot nematode	Cucumber (Figure 5–26), tomato, beet, okra, spinach, others	Sp, Su, F	Swellings are not easily detached from roots. Size variable.	Nematodes in the genusMeloidogyne.
Rust	Sweet corn	Su, F	Small pustules break through the leaf surface, producing dry spores that are brick-red or orange.	Two fungi in the genusPuccinia cause common and southern rusts.
**Southern stem blight, Southern blight, Southern stem rot	Many species (not corn)	Su	Rot on lower stems and other plant parts in contact with soil. In moist weather, a felt-like fan of white fungal growth on the stem (Figure 5–71). Round sclerotia (Figure 5–39) are white at first, turning into tan to brown “bb’s.”.	Sclerotium rolfsii (fungus)
**White mold, Sclerotinia blight, Sclerotinia rot, “Drop” (lettuce)	Crucifers, lettuce, sometimes others	F, W, Sp	Usually light-brown rot of stems and leaves (Figure 5–72). Fluffy white fungal growth. Irregular black sclerotia—similar in shape and color to mouse droppings—eventually form on or within stems.	Sclerotinia sclerotiorum(fungus)

**Until and unless fungal structures develop, stem rots are difficult to distinguish from one another.

FRUITS (TREE AND SMALL)

Note: A wide variety of problems can occur on fruits, and some resemble each other (for example, copper injury, bacterial leaf spot, and scab on peach fruit). Anything beyond the easily recognized diseases on this list should be referred to an experienced agent or to the PDIC. For more information, including recommendations on preventive sprays, see Disease and Insect Management in the Home Orchard.

Problem	Occurs on	Season	Hallmarks	Cause
Bitter rot	Apple	F	Circular rotten spots have a vee-shaped profile when the apple is sliced. Cream-colored to orange spores may exude from tiny dark fruiting bodies.	Two species of the fungus Colletotrichum
Black knot	Stone fruits, esp. plum and cherry	All	Segments of twigs, branches, or trunks become swollen, black, and roughened (Figure 5–73).	Apiosporina morbosa (fungus)
Brown rot (Figure 5–20)	Stone fruits	Su	Smooth, brown rotted areas expand rapidly as fruit mature. Fuzzy gray or tan fungal sporulation develops on the surface.	Species of the fungus Monilinia
Cedar-apple rust	Apple	Late Sp. to Su	Bright yellow and orange leaf spots (Figure 5–74). Small yellow blisters on the upper leaf surface turn dark. Later, spore-producing pustules with frilled edges form on leaf undersides (Figure 5–42). (Use a hand lens to confirm.)	Gymnosporangium juniperi-virginianae
Flyspeck	Apple	Su, F	Dark flecks, each the size of a period, in clusters on the surface of developing and mature fruit.	Schizothyrium pomi (fungus)
Gray mold Also called botrytis blight on many plants	Strawberry	Sp	Fuzzy gray mold on rotting fruit(Figure 5–75). Caution: This can be confused with several other problems if the mold is not yet present.	Botrytis cinerea (fungus) Diagnostic key
Leaf curl	Stone fruits	Sp to early Su	Expanding leaves become twisted and ruffled, often with reddening (Figure 5–76).	Taphrina deformans (fungus)
Mummy berry	Blueberry	Su	Ripening berries turn the cream pink (Figure 5–21) instead of blue. They fall from the plant and eventually shrivel into a dry pumpkin-shaped “mummy.”	Monilinia vaccinii-corymbosi(fungus). More info on blueberry fruit diseases.
Powdery mildew	Many species	Sp, Su, F	White to gray fungal growth on upper and/or lower leaf surfaces. Can also occur on fruit (e.g., peaches, grapes).	Multiple fungi, esp. Podosphaera(rosaceous hosts) and Uncinula(grape)
Sooty blotch	Apple	Su, F	Superficial, irregular dark areas on the skin of developing and mature fruit.	Various fungi

TREES AND SHRUBS

Problem	Occurs on	Season	Hallmarks	Cause
Black spot	Rose	Sp, Su, F	Dark leaf spots with “feathered” borders. Also yellowing and leaf drop (Figure 5–77).	Diplocarpon rosae (fungus)
Boxwood blight (If suspected, send to PDIC for confirmation.)	All boxwood species; also sweetbox and pachysandra	All	On boxwood: Dark-brown leaf spots, dark streaks on green stems, extensive leaf drop starting at the bottom of the plant. On pachysandra, leaf spot.	Calonectria pseudonaviculata(fungus)
Camellia petal blight	Camellia japonica	Sp	Petals turn brown and blossoms drop off. When the base of the flower is removed, a ring of white fungal growth is visible on petal bases.	Ciborinia camelliae (fungus)
Cedar-apple rust	Apple, crabapple	Su	On these hosts, mostly affects leaves. See section on fruit diseases, above.	Gymnosporangium juniperi-virginianae (fungus)
Cedar-apple rust	Eastern redcedar	Sp	Woody, round galls on branches sprout orange gelatinous telial horns in mid-spring after warm rains. Comparison with quince rust (Figure 5–78).	Gymnosporangium juniperi-virginianae (fungus)
Cold injury	Gardenia (Figure 5–79), pittosporum (Figure 5–80), boxwood (Figure 5–81), others	All	Not the same as frost damage to foliage or blooms. Typically, bark loosens or splits, often near the soil line. Dieback and decline may go unnoticed until the shrub is stressed by summer heat.	Extremely low temperatures in late fall or early spring, when stems are not completely dormant
Exobasidium leaf gall	Camellia (Figure 5–24), azalea (Figure 5–82), rhododendron	Sp	Thickening or bulbous growths on new leaves. Whitish-green at first; may darken over time.	Species of Exobasidium (fungus)
Entomosporium leaf spot	Red-tip photinia, Indian hawthorn (Figure 5–83), sometimes pear	All	Bright red leaf spots, whose centers turn gray over time and develop tiny blisters where spores are produced. Leaf drop can be severe.	Diplocarpon mespili (fungus)
Lichens	All trees and shrubs	All	Flat (Figure 5–84), flaky (Figure 5–85), or hairy (Figure 5–86) growths on the bark of branches and trunks (also on rocks). Typically gray to grayish-green in color.	Lichens are symbioses between algae and fungi. They’re often seen on declining plants, but do not cause direct damage.
Normal leaf drop	Southern magnolia, American holly (Figure 5–87), pines	Sp, Su, F	Pines, as well as broadleaved evergreens, shed their 2+-year-old leaves or needles. The time of year depends on the tree species.	Natural aging. No cause for concern unless leaves formed during the last two years are dropping.
Oak leaf blister	All oaks	Sp, Su	Yellow-green to white puckered spots on newly expanded leaves. Spots turn brown in early summer.	Taphrina caerulescens (fungus)
Powdery mildew	Euonymus (Figure 5–37), rose (Figure 5–88), saucer magnolia, dogwood, Leucothoë, spiraea, tulip poplar, many others	Sp, Su, F	White fungal growth on leaf and stem surfaces range from thin to felt-like. Dogwoods in midsummer get brown blotches on leaves (Figure 5–89) (hold edgewise to see the fungus). Leucothoë develops red leaf spots were infected (Figure 5–90).	Multiple fungi, esp. Erysiphe andPodosphaera
Quince rust	Eastern redcedar (Figure 5–91)	Sp	Needles or slight branch swellings develop small orange gelatinous telia in early spring. Comparison with cedar-apple rust (Quince rust on eastern red cedar (Figure 5–78).	Gymnosporangium clavipes(fungus)
Quince rust	Ornamental pear (Figure 5–92)	Su	Pustules (aecia) of orange spores develop on fruit or swollen twigs. Tubular white membranes over the aecia are obvious on fruit.	Gymnosporangium clavipes(fungus)
Shot-hole	Cherry-laurel and flowering cherry	Su, F (All, if on ever-green species)	Leaf spots turn from green to brown and drop out, leaving holes with clean edges (Figure 5–8).	Several fungi and bacteria
Slime flux	White oak, elm, other hardwoods	Su	In the heat of summer, fermented sap oozes from cracks in bark (Figure 5–93). On white oak, this is usually close to the soil line. The sour odor attracts a variety of insects (Figure 5–94).	Anaerobic bacteria cause a condition called wet wood. Gas from fermentation forces sap out
Spot anthracnose (not the same disease as dogwood anthracnose)	Flowering dogwood	Sp	Small red or tan spots develop on showy bracts (Figure 5–95). Bract can be deformed if spots are numerous.	Elsinoë corni (fungus)

HERBACEOUS ORNAMENTALS (ANNUAL AND PERENNIAL)

Problem	Occurs on	Season	Hallmarks	Cause
Dodder	Many hosts	Su, F	Masses of thin, orange strands grow among and attach to stems of the host plant (Figure 5–21). Inconspicuous white flowers may be present.	Parasitic plants in the genusCuscuta
†Impatiens downy mildew	Standard impatiens and its hybrids (not New Guinea)	Su	Leaves yellow and drop (Figure 5–96), leaving only stems that eventually rot. Velvet layer of white spores (Figure 5–97) develops on the underside of leaves in humid weather.	Plasmopara obducens(fungus-like organism)
Leaf streak	Daylily	Su	Leaves turn brown from the tip (Figure 5–98). The leading edge of the dead tissue is in the form of a narrow “V” along the midrib.	Aureobasidium microstictum(fungus)
‡Phytophthora aerial blight	Madagascar periwinkle (annual vinca)	Su	Leaves on individual stems wilt and die, turning gray-green and brown. Leaves do not stick together. Often there are distinct brown or purple lesions on stems (Figure 5–99).	Phytophthora nicotianae(fungus-like water-mold)
Powdery mildew	Coreopsis, gerbera, monarda, sedum, zinnia, and others	Sp, Su, F	White to gray fungal growth on upper and/or lower leaf surfaces (Figure 5–100).	Several different fungi, each specific to a group of plants
Root-knot nematode	Begonia, impatiens, liriope, others	Sp, Su, F	Swellings are not easily detached from roots. Galls tend to be large and numerous in begonia and impatiens (Figure 5–101) but can be small (e.g. in liriope).	Nematodes in the genusMeloidogyne
Rust	Aster, daylily, hollyhock, Jack-in-the-pulpit, oxalis, St. John’s-wort, others	Su, F	Yellow or orange spots on the upper leaf surface (Figure 5–102). Pustules of yellow to orange to reddish brown, dry (often dusty) spores on the underside (Figure 5–103) of each spot.	Many fungi includingPuccinia, Uromyces, andColeosporium; specific to their hosts

†A similar disease affects basil and cucurbits, but we recommend diagnosis at the PDIC when there are foliar problems in those plants.

When Plants Are Wilted

A plant can wilt (droop) during all or part of the day. This is often accompanied by a loss of luster in the green color. When wilting occurs within individual leaves, you may see large tan-colored dead areas between the veins, sometimes extending to entire leaves.

Several problems can lead to wilting. It may be an indication of the following:

The plant lacks sufficient water in the root zone, either because of a lack of rain or irrigation, excessive drainage, or hydrophobic (water-repellent) soil.
Heat and low humidity are causing a plant to transpire moisture more quickly than it is able to pull water from the soil.
Excess soluble salts in the soil—usually because of excess fertilizer applications—are limiting water uptake.
Decay has affected roots or lower stems. Root rot often starts in wet weather, but the wilting may not be apparent until hot, dry weather sets in. At that point, there are not enough healthy roots left to supply the plant’s water requirements.
Root-feeding nematodes have compromised the root system. One common group of nematodes causes visible swellings on roots, but many kinds do not. Nematode feeding may or may not be accompanied by noticeable root decay.
A vascular disease such as southern bacterial wilt or fusarium wilt is interfering with water transport. In these cases, the xylem vessels in the roots or stems are unable to move water up to the leaves, fruits, and other plant parts.
Wilting caused by insect attacks or infectious diseases often starts with just a few plants or even one side of a plant. If most or all plants of a certain kind are affected in a short period of time, it is likely a cultural or environmental issue.

When an herbaceous plant has wilted in the vegetable garden or flower bed in spite of adequate soil moisture in the root zone, the following schematic can be used. It is set up in the format of a “dichotomous key.” Starting at the top, decide whether statement 1a or statement 1b better applies to the situation. Depending on the answer, you will either be directed to a diagnosis or to another set of numbered comparisons. Repeat the process until you reach a diagnosis or recommendation.

1a. Evidence of insect tunneling in stem (insect, webbing, frass, shed skin) insect injury; see chapter 4, “Insects”

1b. No sign of insects feeding in or on stems

2a. Visible decay at the base of the main stem, near the soil line (also check roots)

2b. No visible decay at the base of the main stem

3a. Visible fan of white fungal mycelium (Figure 5–35) and/or small, round, tan sclerotia (Figure 5–39) southern stem blight

3b. Little or no evidence of fungal growth unidentified stem rot;

4a. Roots darkened, decaying, or missing root rot,

4b. Good number of roots present, neither darkened nor decayed

5a. Areas of roots swollen into knots that do not easily detach root-knot nematode

5b. No swellings on roots vascular wilt, nematodes, or excess fertilizer; submit a sample

Note: This text refers to symptoms seen in herbaceous plants in the garden or flower bed. Trees and shrubs can respond differently to the kinds of stresses listed here.

†Normal roots of some plants are naturally dark. A good test for root rot is to tug on a root to see whether the outer portion can be easily pulled off of the central core of vascular tissue.

‡Root knots are reliably large in some plants such as tomato, cucumber, impatiens, and begonia. They may be small and hard to see in some kinds of plants, in which case a clinic diagnosis will be needed.

Principles of Plant Disease Management

Although homeowners and growers are sometimes simply curious to know the cause of a particular disease, most are interested in controlling it. Often no acceptable measures are available that will halt the disease, and the affected plant or plants must be removed. Sometimes the only thing that can be done is to redouble preventive efforts for the next growing season. In other cases, the affected plant will recover by putting out new roots and leaves with or without the application of management measures. Diagnosis of the disease is very important in deciding whether the problem is serious and what measures, if any, will be helpful and cost-effective. The choice of management measures is influenced by where the pathogen overwinters, how it spreads, its host range, and how the conditions favoring infection. See the previous sections on Disease Development and Spread and Survival of Pathogens.

In many cases, it is not realistic to talk about disease control. We do not have complete control over nature, even in our own backyards. Thus, the sections that follow will discuss the two main types of disease management strategies: cultural and chemical. Many homeowners and growers today are interested in biological methods of dealing with pests. Unfortunately, there are very few biological options for plant disease management in the yard and garden at the present time. At the end of the chapter, we will pull these ideas together within the framework of integrated pest management using a case study model.

Cultural Management

We often hear these sayings about managing problems: “A stitch in time saves nine.” Or “An ounce of prevention is worth a pound of cure.” Taken literally, this means that what we do to prevent disease is 9 to 16 times more effective than dealing with a disease after it has become established. Many of these preventive measures fall under the category of cultural practices, the actions we take every day as part of growing plants. A summary of the top practices for disease management in the garden is given in the highlighted box. Notice that all but one are cultural methods.

Follow the “right-plant-right-place” approach. Before planting, carefully study the site. Does it have the appropriate amount of sun exposure, drainage, and soil for a chosen plant to thrive? Boxwoods and dogwoods, for instance, prefer light shade. Although they may appear to tolerate full sun, it predisposes them to problems. Azaleas and daphne need good drainage to avoid root rot.

Besides adaptability to your soils and climate, look for plants that are not susceptible to common diseases. Even within susceptible species, look for varieties and hybrids that offer resistance to key diseases. For example, there are apple cultivars that are resistant to cedar-apple rust, dogwood cultivars resistant to powdery mildew, rose cultivars resistant to black spot and cercospora leaf spot, and tomato cultivars resistant to nematodes and some fungal wilts. Heirloom tomato varieties have become increasingly popular but may lack resistance to soilborne diseases. In this case, grafting is an option. For more information, see the Grafting for Disease Resistance in Heirloom Tomatoes by Cary Rivard and Frank Louws (AG-675), and keep an eye out for a grafting workshop near you.

Plant with an eye toward diversity. If all the plants in the vicinity are of the same type, a disease can spread quickly. Diversified plantings are less likely to suffer major disease problems. You could, for instance, use groups of different shrubs for a screen rather than just Leyland cypress or Japanese cedar.

Rotate crops to try to break the disease cycle. Change the location in the garden where crops are planted from one year to the next. Vegetable crops in the same family, such as cabbage and broccoli, should not follow each other in the same spot in the garden. The length of an effective rotation will depend on the disease involved, so get a diagnosis. Some pathogens, unfortunately, do not disappear over time. An example is Ralstonia solanacearum, the cause of southern bacterial wilt. Once introduced it will remain in the soil indefinitely.

Improving the soil will reduce plant stress and decrease soilborne diseases. Good soil drainage, proper soil pH, and optimum fertility produce healthy plants that are more resistant to insects, diseases, and environmental stresses. Soil testing will reveal pH and nutritional problems that can reduce growth and lead to plant stress. Learn more about soil testing in chapter 1, Soils and Plant Nutrients. Planting in beds raised 6 to 8 inches above grade and adding organic amendments to the soil can significantly reduce problems with phytophthora root rot.

Buy seed from a reputable source, and inspect all transplants, including the roots, before planting. Boxwood blight finds its way into landscapes in North Carolina by the installation of new, infected plants.

Among plant pathogens, most nematodes, many fungi, some bacteria, and a few viruses are soil inhabitants. Take care not to move soil among landscapes or gardens on borrowed or rented tools or equipment. For the same reason, transplanting shrubs or perennials from one location to another risk transplanting pathogens as well as the plant.

Plant and harvest at recommended times, to give every advantage to the plant. For example, Madagascar periwinkle (Catharanthus roseus) should not be planted until the soil has warmed in the spring. Planting when the soil is cold and wet can also cause okra seeds to rot in the ground. While late plantings of squash are very likely to suffer from powdery mildew, pansies should not be transplanted until the soil temperature has cooled in the fall.

Because water is the major limitation for bacteria and most fungi, be careful with irrigation. Overwatering favors water mold species like Phytophthora andPythium and the root rots they cause. Avoid wetting leaves and stems if possible to prevent foliar diseases. If overhead watering cannot be avoided, at least water during times that will not add hours to the natural nighttime leaf wetness period. Space and prune plants properly to improve air circulation and help the foliage dry quickly.

In some cases, prompt removal of diseased plants or plant parts can reduce the amount of a pathogen in the vicinity. For example, the removal of diseased tomato leaves can slow the progress of septoria leaf spots. If a tree or shrub in a hedge planting has been diagnosed with armillaria root rot, the individuals on either side should also be removed, because they have likely been infected via fungal growth through the soil. The same strategy would be of little benefit with Phytophthora root rot because the spores of Phytophthora species can move far beyond the initial infection in water runoff.

Remove plant debris in the fall to reduce pathogen populations. Many fungal foliar pathogens overwinter in dead leaf litter. In the case of fallen camellia blossoms, rake them up in the spring. Sclerotia of the camellia petal blight fungus, Ciborinia camelliae, survive the whole year on the ground’s surface after the blossoms rot away. The sclerotia resume growth and release spores in the spring, to coincide with the emergence of camellia blossoms. In the vegetable garden, remove roots if they were infested with nematodes or root rot pathogens. Liriope (Liriope muscari) should be trimmed close to the ground in late winter to reduce the carryover of anthracnose on foliage from one year to the next. Fire blight, brown rot, and many other fruit diseases overwinter in cankers. Even the fungus that causes black spots on roses can overwinter on canes as well as fallen leaves. Prune and remove cankers during the dormant season by removing 4 to 6 inches into clean wood. When pruning out active fireblight infections in the spring, be more aggressive, going 10 to 12 inches below the visible damage. Destroy the clippings, or at least remove them from the site, and sanitize shears frequently. See the NC State Extension sanitizers table for more information.

When composting, turn the pile thoroughly so it reaches a high enough temperature to kill pathogenic fungi, bacteria, and nematodes. Even though compost pile temperatures might get high enough to kill pathogens, you should never knowingly place infected plant material in the compost pile. Read more about composting in chapter 2.

If pathogens are present, cultivate flower beds and vegetable gardens. Cultivation can expose soil insects and disease organisms to desiccation, cold temperatures, and predation.

A 2-to-3-inch layer of mulch acts as a barrier between the soil and the plant and may prevent inoculum-infested soil from splashing onto the plants during watering or heavy rain. Mulching will also enhance the total health and vigor of most plants. Late winter mulching can reduce camellia petal blight and the early infections of black spots on roses. In both cases, the mulch covers overwintering fungal structures so that spores are not released into the air.

Many pathogens take advantage of wounds to enter, so avoid any unnecessary injury. This is especially important with trees, where roots are often disturbed by digging, and the consequences may take years to develop.

Remove weeds while they are young. Some weeds can harbor diseases and arthropod vectors. Mow or destroy weeds from ditch banks and other nearby areas. Till the planting area early, so weeds that might carry pests have time to die before you plant.

A physical barrier can protect certain plants. Tomatoes, peppers, and eggplants benefit from this technique; they can be protected from cutworms and the soilborne disease southern blight. Wrap the stem of transplants with a 4-by-4-inch strip of aluminum foil so that 2 inches of the stem is protected above and below the ground.

A solid planting of French marigolds (Tagetes patula) will give good control of many kinds of root-knot nematodes. Details of the practice can be found in the NCDA&CS publication NemaNote 1. A common misconception is that a sprinkling of marigolds can discourage nematodes. In fact, planting only a few marigold plants in a vegetable garden will provide little or no control.

Solarization is an approach that involves heat-treating the soil using energy from the sun to reduce populations of nematodes, weeds, and soilborne fungi. It has potential benefits in approximately the eastern half of North Carolina. The soil should be covered with plastic for at least four weeks, preferably longer, during a hot and sunny time of the year. Frequent cooling by rain and cloudy periods will reduce the benefits.

To achieve maximum results, follow these recommendations:

Till the soil well before covering it with plastic to destroy clods and plant debris, which might interfere with uniform conduction of heat through the soil and protect some organisms from the full effects of the treatment.
Make sure the soil is moist when you apply the plastic cover. Wet soil conducts heat better than dry soil. Also, most pest organisms are more susceptible to the lethal effects of heat in moist soil; they may be dormant if dry.
Raise the center of the bed so that it forms a small crown or peak to enable the plastic to shed water. Water standing on the plastic will absorb some of the heat intended for the soil.
Use clear plastic instead of black plastic. Clear plastic produces higher temperatures faster than black plastic.
Use thin plastic (1 to 2 millimeters), which permits more sunlight to penetrate to the soil and has been reported to affect more rapid and deeper control for soilborne fungi than thicker plastic (6 millimeters).
Leave the plastic cover on until planting time. It has no detrimental effects on the soil and will reduce the chances of recontamination before planting.
Avoid bringing contaminated plants or untreated soil into the treated bed when planting, and do not till or otherwise disturb treated soil. Deep tillage can bring soil up from depths that were not adequately heated.

Chemical Management

Prevention and sanitation are the most practical approaches to disease control and have been detailed in the previous section. Home gardeners have few alternatives for chemically controlling plant diseases, and almost all of those alternatives are directed against fungi. Although the products used are called fungicides, they slow down rather than eliminate fungi. There are few, if any, chemical options for consumers to use against bacteria, nematodes, and viruses.

Fungicides are often unnecessary because many diseases cause only minor aesthetic damage. In other cases, fungicides may be impractical to apply. They are of no value against cankers or root rots in trees and shrubs. However, fungicides can be an important component of IPM in some situations. It is impossible to control black spots on susceptible rose cultivars without fungicides. A homeowner with a peach or apple tree will need a high tolerance for damaged fruit if he or she chooses not to spray. Fungicides can also be important tools in the management of certain turfgrass diseases.

No single fungicide will control all fungi, though some have a wider spectrum of activity than others. Most fungicides are protectants and should be applied before a pathogen infects a plant. Furthermore, many do not move within the plant and so must be applied repeatedly to protect new growth. Some fungicides are systemic and can cure early infections.

For a fungicide to be a useful tool, the disease must be properly diagnosed and the right chemical must be applied in a timely manner, at the correct dose, with good coverage, and at the necessary intervals.

Do not expect miracles from fungicides. For example, fungicides applied after powdery mildew is present on a leaf will not return the leaf to its original green color. A fungicide can, however, protect new growth from becoming infected.

Fungicide Classification

Fungicides can be classified by their topical mode of action (how they interact with the plant) or their biochemical mode of action (how they affect the target fungus).

There are four basic topical modes of action.

Contact fungicides. These are strictly protectants and must be on the surface of the plant before infection takes place. They break down and wash off over time and so must be reapplied fairly frequently, usually every 7 to 10 days. Reapplication is also necessary because new growth is not protected.
Translaminar fungicides (local penetrants). These compounds will move into and across a leaf but not up or down in the plant.
Acropetal penetrants. These fungicides will enter the plant and move from the point of entry in an upward direction only, with the transpiration stream.
True systemics. Only one group of fungicides—the phosphonates—will move downward from the point of application. One implication is clear: For most fungicides, if you want activity in the crown or roots, you have to apply to the crown or roots!

There are dozens of biochemical modes of action, but they can be conveniently grouped into two groups: “multisite” and “single-site” modes of action. Fungicides classified as having “multisite” modes of action are all broad-spectrum protectants with a contact topical mode of action. These chemicals disrupt a wide array of life processes in the fungal cell. On the other hand, fungicides with “singlesite” modes of action affect very specific biochemical processes in the fungal cell. They usually have a narrower spectrum of activity and are often—but not always—local or acropetal penetrants. One limiting factor in using these compounds is that some fungal populations can evolve to be less sensitive, or have a resistance to a compound after repeated use (see below).

Recent years have shown increased interest in chemicals that have fungicidal activity but are not fungicides in the traditional sense. Examples in this category include petroleum-based horticultural oils, neem oil (derived from the neem tree), and potassium bicarbonate (a relative of baking soda, used primarily against powdery mildew). When used against certain diseases, these chemicals can be adequate alternatives to conventional fungicides when the disease pressure is not too great. Keep in mind that neem is toxic to bees.

The repeated use of pesticides can lead to the evolution of insensitive pest populations, whether they are fungi, bacteria, insects, weeds, or rodents. In such cases, individual pests are not becoming stronger. Instead, chance mutations result in resistant individuals, which are the ones that survive and reproduce. Whether and how fast resistance becomes widespread enough in a population to result in loss of control depends on the biochemical mode of action of the pesticide, the life history of the pest, its reproductive rate, and the intensity of pesticide use.

Fungicide Timing

The timing of fungicide applications is an important component in chemical disease control. Fungicides should be applied when conditions favoring disease development are present.

Rainy, foggy, warm, and humid weather conditions generally favor disease development. Whenever possible, spray schedules should be adjusted to provide fungicide protection before rainy periods, and fungicides should be reapplied after heavy rains if the label so indicates.

When using chemical management, we need to know the life cycle of the disease organism and when it is most susceptible. Many fruit diseases are best managed when the fruit is very young, or even in the blossom stage; once the fruit starts to rot, it is too late. A diagnosis at that time can at least help a gardener plan management strategies for the next season.

Always carefully read and follow the label when using any pesticide.

USDA Plant Hardiness Zone Map

The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.

For the first time, the map is available as an interactive GIS-based map, for which a broadband Internet connection is recommended, and as static images for those with slower Internet access. Users may also simply type in a ZIP Code and find the hardiness zone for that area.

No posters of the USDA Plant Hardiness Zone Map have been printed. But state, regional, and national images of the map can be downloaded and printed in a variety of sizes and resolutions.

http://planthardiness.ars.usda.gov/PHZMWeb/

The Role of Phosphorus (P)

Phphosphorus_deficiency1osphorus is a vital component of adenosine triphosphate (ATP), the ‘energy unit’ of plants. ATP forms during photosynthesis, has P in its structure, and processes from the beginning of seedling growth through to the formation of grain and maturity.

Periodic Table of Crop Nutrients and Deficiencies

Periodic Table of Crop Nutrients

17 nutrients are essential for plant health. Optimal yields can only be produced when all these nutrients are in proper supply. According to the Law of Minimum, if one or more nutrients are lacking in the soil, crop yields will be reduced, even though an adequate amount of other elements is available.

Plumeria Nutrient Deficiencies

Not all plumeria problems are caused by insects or diseases. Sometimes an unhealthy plumeria is suffering from a nutrient deficiency or even too much of any one nutrient. Plumeria nutrient deficiencies often manifest as foliage discoloration or distortion. The following chart outlines some possible problems. Unfortunately many problems have similar symptoms and sometimes it is a combination of problems.

Be sure you eliminate the obvious before you kill your plumeria with kindness.

Check first for signs of insects or disease.
Foliage discoloration and stunted plants can easily be caused by soil that is too wet and drains poorly or soil that is too compacted for good root growth.
Exposure to cold or heat will slow plant growth and effect flowering.
Too much fertilizer can result in salt injury. Your plants may look scorched or they may wilt, even when the soil is wet.

Plumeria require a mix of nutrients to remain healthy. Nutrients that are needed in relatively large amounts are called the macronutrients. Plant macronutrients include: (N) nitrogen, (P) potassium, (K) phosphorus, calcium, sulfur and magnesium.

There are a handful of additional nutrients that are required for plant growth, but in much smaller quantities. These micronutrients include: boron, copper, iron, manganese, molybdenum and zinc.

All of these nutrients are taken in through the roots. Water transfers the nutrients from the soil to the Plumeria roots. So one requirement of sufficient Plumeria nutrition is water. A second requirement is the appropriate soil pH for the Plumeria being grown. Each Plumeria prefers a specific pH range to be able to access the nutrients in the soil. Some Plumeria are fussier than others, but if the soil pH is too acidic or alkaline, the Plumeria will not be able to take in nutrients no matter how rich your soil may be.

Primary Macronutrients

Nitrogen (N)

Nitrogen (N) is essential for plant growth and is part of every living cell. It plays many roles in plants and is necessary for chlorophyll synthesis. Plants take up most of their N as the ammonium (NH₄⁺) or nitrate (NO₃^–) ion. Some direct absorption of urea can occur through the leaves, and small amounts of N are obtained from materials such as water-soluble amino acids.

Symptoms: Lack of N and chlorophyll means the plant will not utilize sunlight as an energy source to carry on essential functions such as nutrient uptake. Older leaves, generally at the bottom of the plant, will yellow. Remaining foliage is often light green. Stems may also yellow and may become spindly. Growth slows.
Sources: Any compound containing the words: ‘nitrate’, ‘ammonium’ or ‘urea’. Also manure.
Notes:
- Many forms of nitrogen are water soluble and wash away.
- Nitrogen is a component of vitamins, amino acids and energy systems within the plant, which form its proteins. Thus, N is directly responsible for increasing protein content in plants.
- Nitrogen is necessary for chlorophyll synthesis and, as a part of chlorophyll molecules, is involved in photosynthesis.
- Nitrate is very mobile in the soil and moves with soil water to root surfaces for plant absorption.

Phosphorus (P)

One of three primary nutrients, phosphorus (P) is essential for plant growth, and a plant must access it to complete its normal production cycle. Plants absorb P from the soil as primary and secondary orthophosphates (H₂PO₄^– and HPO₄^2-).

Symptoms: Small leaves that may take on a reddish-purple tint. Leaf tips can look burnt and older leaves become almost black. Reduced fruit or seed production.
Sources: Compounds containing the words ‘phosphate’ or ‘bone’. Also green sand.
Notes:
- Very dependent on pH range.
- The highest levels of P in young plants are found in tissue at the growing point. As crops mature, most P moves into the seeds, fruit, or both.
- Under P deficiency, some crops, such as corn, tend to show abnormal discoloration.
- Phosphorus is noted especially for its role in capturing and converting the sun’s energy into useful plant compounds.
- Phosphorus promotes root development and early seedling growth.
- Research associates specific growth factors with P: stimulated root development, increased stalk and stem strength, and improved flower formation and seed production.

Potassium (K)

Potassium (K) is one of the essential nutrients and is taken up in significant amounts by crops. Potassium is vital to photosynthesis, protein synthesis and many other functions in plants. It’s classified as a macronutrient, as are nitrogen (N) and phosphorus (P). Plants take up K in its ionic form (K⁺).

Symptoms: Older leaves may look scorched around the edges and/or wilted. Interveinal chlorosis (yellowing between the leaf veins) develops.
Sources: Compounds containing the words ‘potassium’ or ‘potash’.
Notes:
- Potassium enhances many enzyme actions aiding in photosynthesis and food formation. It builds cellulose and helps translocate sugars and starches. Potassium is vital to producing grains rich in starch.
- Potassium maintains turgor and reduces water loss and wilting.
- Potassium is known as the “quality nutrient” because of its important effects on factors such as size, shape, color, taste, shelf life, fiber and other quality-related measurements.
- In many high-yielding crops, the K content in the plant is comparable to the nitrogen (N) content.
- Potassium is absorbed by plants in the ionic form, indicated as K⁺.
- Plants deficient in K are less resistant to drought, extreme temperatures and other stressors. Plants lacking K are also more susceptible to pests, diseases and nematode attacks.
- Ample K can increase root growth and improves drought tolerance.

Secondary Macronutrients

Magnesium (Mg)

Hidden in the heart of each chlorophyll molecule is an atom of magnesium (Mg), making the nutrient actively involved in photosynthesis. Magnesium also aids in phosphate metabolism, plant respiration and the activation of many enzyme systems.

Symptoms: Slow growth and leaves turn pale yellow, sometimes just on the outer edges. New growth may be yellow with dark spots.
Sources: Compounds containing the word ‘magnesium’, such as Epson Salts.
Notes:
- Magnesium is mobile within the plant and moves easily from older to younger tissues.
- Plants require Mg to capture the sun’s energy for growth and production through photosynthesis.
- When Mg deficiencies occur, the lower (older) leaves are affected first.
- The most common source of Mg is dolomitic limestone, which provides both calcium and Mg, while neutralizing soil acidity.
- Magnesium acts as a phosphorus carrier in plants, and is required for better root formation and thus for better nutrient and water efficiency in plants.

Calcium (Ca)

Calcium (Ca) is found all around us, and the very existence of plants and animals depends on it. Plants take up Ca as the Ca²⁺ cation. Once inside the plant, Ca functions in several essential ways.

Symptoms: New leaves are distorted or hook shaped. The growing tip may die. Contributes to blossom end rot in tomatoes, tip burn of cabbage and brown/black heart of escarole & celery.
Sources: Any compound containing the word ‘calcium’. Also gypsum.
Notes:
- Not often a deficiency problem and too much will inhibit other nutrients.
- Calcium deficiencies occur most often in acidic, sandy soils from which Ca leaches via rain or irrigation water.
- Calcium helps balance organic acids within the plant as well as activates several plant enzyme systems.
- Calcium helps form the compounds that make up part of cell walls, which in turn, strengthen the plant structure.
- Calcium builds yields by indirectly improving root growth conditions and stimulating microbial activity, molybdenum (Mo) availability and uptake of other nutrients.
- Calcium helps enable nitrogen (N)-fixing bacteria that form nodules on the roots of leguminous plants to capture atmospheric N gas and convert it into a form plants can use.
- Calcium stimulates root and leaf development, and affects uptake and activity of other nutrients.

Sulfur (S)

Sulfur (S) is a part of every living cell and is important in the formation of proteins. Unlike the other secondary nutrients like calcium and magnesium (which plants take up as cations), S is absorbed primarily as the SO₄^2- anion. It can also enter plant leaves from the air as dioxide (SO₂) gas.

Symptoms: New growth turns pale yellow, older growth stays green. Stunts growth.
Sources: Compounds containing the word ‘sulfate’.
Notes:
- More prevalent in dry weather.
- Sulfur is present in several organic compounds that give the characteristic odors to garlic, mustard and onion.
- Sulfur appears in every living cell and is required for synthesis of certain amino acids (cysteine and methionine) and proteins.
- Sulfur is also important in photosynthesis and for winter crop hardiness.
- Although S isn’t a constituent of cholrophyll, it’s still vital in chlorophyll formation.
- Sulfur aids in seed production.
- Leguminous plants need S for efficient nitrogen fixation.

Micronutrients

Boron (B)

Boron (B) is a micronutrient that is essential for cell wall formation and rapid growing points within the plant, such as reproductive structures. Interestingly, while higher plants require B, animals, fungi and microorganisms do not need this nutrient.

Symptoms: Poor stem and root growth. Terminal (end) buds may die. Witches brooms sometimes form.
Sources: Compounds containing the words ‘borax’ or ‘borate’.
Notes:
- Boron improves seed set under stressful conditions.
- Although required in small amounts, boron is a component of all cell walls in the plant.
- Boron deficiencies are more pronounced during drought periods, when root activity is restricted.
- The line between deficiency and toxicity is narrower than other essential nutrients. Farmers should apply at proper rate and with proper placement.
- Plumeria most effectively uses boron when it’s applied through broadcast soil applications.

Chlorine (Cl)

Plants take up chlorine (Cl) as the chloride (Cl^–) anion. It’s active in energy reactions in the plant. Most Cl in soils comes from salt trapped in parent materials, marine aerosols and volcanic emissions. Classified as a micronutrient, Cl is required by all plants in small quantities.

Symptoms:
Sources:
Notes:
- Stomata regulate the release of moisture from plants so they can minimize water loss during stressful dry periods. Chloride is key in stomatal regulation.
- Chloride is involved in the chemical breakdown of water in the presence of sunlight and activates several enzyme systems.
- Chloride plays an important role in plants as they acclimate to changing water availability (or make osmotic adjustments).
- Chloride supports the transport of nutrients such as calcium, magnesium and potassium within a plant.

Copper (Cu)

Copper (Cu) activates enzymes and catalyzes reactions in several plant-growth processes. Vitamin A production is closely linked to the presence of Cu as well, and it helps ensure successful protein synthesis. Classified as a micronutrient, only a small amount of this essential nutrient is needed for plant survival.

Symptoms: Stunted growth. Leaves can become limp, curl, or drop. Seed stalks also become limp and bend over.
Sources: Compounds containing the words ‘copper’, ‘cupric’ or ‘cuprous’.
Notes:
- Copper is the most immobile of the micronutrients.
- Many vegetable crops show Cu hunger, with leaves that lose turgor and develop a bluish-green shade before becoming chlorotic and curling.
- Copper is necessary to chlorophyll formation in plants and catalyzes several other plant reactions.
- Other metals in the soil, such as iron, manganese and aluminum, affect the availability of Cu for plant growth.
- Organic soils are the most vulnerable to Cu deficiency; heavy, clay-type soils are least vulnerable.

Manganese (Mn)

Manganese (Mn) functions primarily as part of enzyme systems in plants. It activates several important metabolic reactions and plays a direct role in photosynthesis. Manganese accelerates germination and maturity while increasing the availability of phosphorus (P) and calcium (Ca).

Symptoms: Growth slows. Younger leaves turn pale yellow, often starting between veins. May develop dark or dead spots. Leaves, shoots and fruit diminished in size. Failure to bloom.
Sources: Compounds containing the words ‘manganese’ or ‘manganous’
Notes:
- Manganese plays a vital role in photosynthesis by aiding in chlorophyll synthesis.
- Soybeans and wheat in particular require more Mn than many crops.
- Manganese is very immobile in plants, so deficiency symptoms appear first on younger leaves, with yellowing between the veins. Sometimes a series of brownish-black specks appear.
- Although Mn deficiencies are often associated with high soil pH, they may result from an imbalance with other nutrients such as calcium (Ca), magnesium (Mg), and Iron (Fe).
- Manganese deficiencies are most common in high organic matter soils and in those soils with naturally low Mn content and neutral to alkaline pH.

Iron (Fe)

Iron (Fe) is essential for crop growth and food production. Plants take up Fe as the ferrous (Fe²⁺) cation. Iron is a component of many enzymes associated with energy transfer, nitrogen reduction and fixation, and lignin formation.

Symptoms: Plants deficient in Fe will often display a pale green leaf color (chlorosis), with sharp distinction between green veins and yellow interveinal tissues. Iron deficiencies may be caused by an imbalance with other metals such as copper (Cu), manganese (Mn) and molybdenum (Mo).
Sources:
Notes:
- Iron deficiencies may be caused by an imbalance with other metals such as copper (Cu), manganese (Mn) and molybdenum (Mo).
- Plants deficient in Fe will often display a pale green leaf color (chlorosis), with sharp distinction between green veins and yellow interveinal tissues.
- Most Fe fertilizer sources work best applied as foliar sprays.
- Iron is a catalyst to chlorophyll formation.
- Iron acts as an oxygen carrier in the nodules of legume roots.

Molybdenum (Mo)

Molybdenum (Mo) is a trace element found in the soil and is required for the synthesis and activity of the enzyme nitrate reductase. Molybdenum is vital for the process of symbiotic nitrogen (N) fixation by Rhizobia bacteria in legume root modules. Considering Mo’s importance in optimizing plant growth, it’s fortunate that Mo deficiencies are relatively rare in most agricultural cropping areas.

Symptoms: Older leaves yellow, remaining foliage turns light green. Leaves can become narrow and distorted.
Sources: Compounds containing the words ‘molybdate’ or ‘molybdic’.
Notes:
- Sometimes confused with nitrogen deficiency.
- Molybdenum-deficiency symptoms show up as a general yellowing and stunting of the plant. A Mo deficiency can also cause marginal scorching and cupping or rolling of leaves.
- Several materials supply Mo and can be mixed with nitrogen (N), phosphorus (P) and potassium (K) fertilizers applied as foliar sprays or used as a seed treatment. Seed treatment is the most common way of correcting Mo deficiency because of the very small amounts of the nutrient required.
- Plants take up Mo as the MoO₄^2- anion.
- Molybdenum becomes more available as soil pH goes up, the opposite of most other micronutrients
- Excessive Mo is toxic, especially to grazing animals.

Zinc (Zn)

Zinc (Zn) is taken up by plants as the divalent Zn²⁺ cation. It was one of the first micronutrients recognized as essential for plants and the one most commonly limiting yields. Although Zn is required in small amounts, high yields are impossible without it.

Symptoms: Yellowing between veins of new growth. Terminal (end) leaves may form a rosette.
Sources: Compounds containing the word ‘zinc’.
Notes:
- Can become limited in higher pH.
- Protein synthesis and growth regulation require Zn. Reduced hormone production due to a Zn-deficient plant will cause the shortening of internodes and stunted leaf growth.
- Zinc is much less mobile within the plant, so deficiency symptoms first appear on the younger leaves.
- Zinc aids synthesis of plant-growth substances and enzyme systems, and is essential for promoting certain metabolic reactions, which are particularly critical in the early growth stages.
- As soil pH increases, zinc availability decreases.

Nickel (Ni)

Nickel (Ni) was added to the list of essential plant nutrients late in the 20th century. Plants absorb Ni as the divalent cation Ni²⁺. It is required in very small amounts, with the critical level appearing to be about 0.1 parts per million.

Notes:
- No Ni deficienceies have been observed under crop-growing conditions, but in crop research settings, ag scientists have reproduced deficiency symptoms such as chlorosis of young leaves and dead meristematic tissue.
- Nickel deficiency has been observed in some nursery plants and tree crops. Affected trees develop mouse-ear, a condition marked by small, curled leaves and stunted growth.
- Nickel is a component of the urease enzyme and is, therefore, necessary for the conversion of urea to ammonia (NH₃) in plant tissue, making it important in plant nitrogen (N) metabolism.

Non-fertilizer Elements

Hydrogen (H)

Hydrogen (H), derived almost entirely from water, is one of the 17 essential nutrients necessary for plant growth. Hydrogen, along with carbon and oxygen, are the three primary elements plants use in the largest amounts, and they perform as the building blocks for plant growth.

Notes:
- Nearly all organic compounds also contain H atoms, which explains why plants need the H they get from water molecules through photosynthesis.
- Hydrogen ions are vital in both aiding proton gradients to help drive the electron transport chain in photosynthesis, and for plant respiration.
- Hydrogen is necessary for building sugars and other molecules to produce glucose for plant energy.
- Known as a structural element, H is present in both the atmosphere and the growing environment.
- Hydrogen is rarely a limiting nutrient.
- Hydrogen is an element and can be a compound as well. As an element, H is the lightest, with one proton, one electron and usually no neutrons. Compound H forms when two H atoms share an electron pair, creating a covalent bond, which takes the form of a gas.

Carbon (C)

Carbon (C) is responsible for all life on earth. Carbon dioxide (CO₂) released into the atmosphere is recycled endlessly as part of the carbon cycle. Plants take CO₂ from the air and use the C for energy, helping to build essential biological compounds such as carbohydrates and proteins.

Notes:
- Carbon is the primary energy source and building block for plant tissues.
- Converted through photosynthesis into simple sugars, C helps plants build starches, carbohydrates, cellulose, lignin and protein.
- Crop residues, green manures and animal wastes can be significant sources of organic C in the soil.
- Almost half of the plant’s dry matter is comprised of C.

Oxygen (O)

Oxygen (O) is responsible for cellular respiration in plants. Plants acquire O by breaking down carbon dioxide (CO₂) during photosynthesis and end up releasing the majority of it as an unnecessary byproduct, saving a small portion for future energy.

Notes:
- All Oxygen available to life on Earth comes from plants.
- Most of the Oxygen plants take in is expelled as a byproduct. Only a very small amount is actually used by the plant for respiration.
- Plants don’t absorb Oxygen from the air, but instead acquire it during the breakdown of carbon dioxide (CO₂) as part of photosynthesis.
- Oxygen interacts with nitrogen (N) in a process called denitrification, and it affects other elements’ oxidation states as well.
- Only the leaves and stems of a plant acquire Oxygen through photosynthesis. The roots of a plant are forced to take in Oxygen from the environment through air spaces in the soil.

The Role of Nitrogen (N)

Nitrogen (N) is essential for plant growth and is part of every living cell. It plays many roles in plants and is necessary for chlorophyll synthesis. Plants take up most of their N as the ammonium (NH4+) or nitrate (No3-) ion. Some direct absorption of urea can occur through the leaves, and small amounts of N are obtained from materials such as water-soluble amino acids.

Plumeria – Frangipani mosaic virus

196
August 1978

Family: Virgaviridae
Genus: Tobamovirus
Species: Frangipani mosaic virus
Acronym: FrMV

Frangipani mosaic virus

A. Varma – Division of Mycology and Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, India

A. J. Gibbs – Research School of Biological Sciences, Australian National University, Canberra, Australia

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap

Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

Described by Francki, Zaitlin & Grivell (1971).
Synonym: Temple tree mosaic virus. A virus with tubular particles 300 nm long and 18 nm in diameter. Sap transmissible. No vector known; is spread in cuttings of infected frangipani (Plumeria spp.). Restricted host range, grows best at 30-35°C.

Main Diseases

In Plumeria acutifolia the virus causes mosaic, ringspots, veinbanding and bronzing. In P. alba, it causes ringspots, leaf distortion and necrosis. No flower symptoms.

Geographical Distribution

Common in eastern Australia and northern India.

Host Range and Symptomatology

Host range not yet tested extensively, but seems restricted. More species become infected at temperatures above 25°C than below. At 35°C symptoms show in 3-6 days, at 22°C they take 2 weeks or more.

Diagnostic species: Datura stramonium. Chlorotic, necrotic or black lesions develop in inoculated leaves after 1-2 weeks in the glasshouse at 22°C. At 35°C, in controlled environment cabinets, similar symptoms develop in 3 days; one strain causes systemic necrosis along the veins and leaf margins.; Nicotiana glutinosa. At 22°C inoculated leaves develop chlorotic lesions in about 2 weeks. Not infected systemically.; N. tabacum (tobacco) cvs Samsun, Virginia Gold or White Burley. Rarely infected at 22°C. At 35°C all strains induce bright chlorotic or necrotic ringspots in inoculated and systemically infected leaves.; N. clevelandii x N. glutinosa. Not infected at 22°C. At 35°C inoculated leaves develop faint chlorotic lesions which become necrotic or develop ringspots. Not infected systemically.
Propagation species: Nicotiana glutinosa. Inoculated leaves give a good yield after 2-3 weeks at 22°C.
Assay species: Datura stramonium is the most reliable assay species.

Strains

Three distinct strains from different provenances have been distinguished by the symptoms they produce. They are the Adelaide strain (Adel) (Francki et al., 1971), and the Allahabad (Ald) and Delhi (Del) strains (A. Varma & A. J. Gibbs, unpublished data). Leaves of D. stramonium kept at about 22°C develop faint chlorotic lesions after inoculation with strain Adel, necrotic lesions after inoculation with strain Ald, and chlorotic lesions, later becoming black, after inoculation with strain Del. At 35°C symptoms developed more quickly and spread more: strain Adel gave necrotic lesions, strain Ald gave lesions with chlorotic haloes or ringspots, and strain Del gave spreading black necrotic ringspots and systemic veinal and marginal necrosis. N. tabacum cv. Virginia Gold was susceptible at 22°C to strain Del only, showing chlorotic and necrotic local lesions. At 35°C in the same tobacco cultivar, strain Adel gave faint necrotic ringspots, strain Ald gave bright necrotic ringspots and strain Del gave large ringspots both in inoculated and in tip leaves.

Transmission by Vectors

No vector is known.

Transmission through Seed

Not transmitted through seed of D. stramonium or N. tabacum cv. Samsun.

Serology

Particles of the virus are strongly immunogenic. They give flocculent precipitates in tube precipitin tests, and form one band of precipitate in gel diffusion tests.

Relationships

Properties, serological relationships and particle morphology place the virus in the tobamovirus group. The particles of frangipani mosaic virus are morphologically indistinguishable from those of other tobamoviruses. The Adel, Ald and Del strains are serologically closely related to each other. All three strains are related distantly to cucumber virus 4, cucumber green mottle mosaic virus, and an isolate of sunn-hemp mosaic virus from Queensland, Australia (but not one from West Africa); and even more distantly to TMV-type strain, TMV-U2 strain, tomato mosaic virus and ribgrass mosaic virus. (A. J. Gibbs & A. Varma, unpublished data; Franckiet al., 1971). There was no detectable serological relationship with Sammons’ opuntia virus even though comparisons of coat protein composition indicate a close affinity (Description No. 184).

Stability in Sap

Very stable. Sap from infected D. stramonium was not infective after heating to 95°C for 10 min, and lost 90% of its infectivity in 10 min at 90°C. The sap was still infective after 10 weeks at room temperature, and at dilutions up to 10^-5.

Purification

The virus is easily purified from infected leaves of frangipani or N. glutinosa by several methods. The following methods give good yields:

1. Francki et al. (1971), based on McLean & Francki (1967) and Francki & McLean (1968). Homogenise infected leaves of N. glutinosa in 1.5 volumes of 0.2 M Na₂HPO₄, clarify by adsorption with charcoal and DEAE cellulose and filter through Celite. Sediment the particles by centrifuging at 44,000 g for 90 min. Resuspend pellets in distilled water and emulsify with equal volume of chloroform. Centrifuge at 12,000 g for 10 min. Collect aqueous layer and sediment the particles by centrifuging at 16,000 g for 30 min. Repeat chloroform extraction and sedimentation.

2. Based on Varma, Gibbs & Woods (1970). Triturate infected leaves mechanically with 2 ml/g of neutral phosphate-ascorbate buffer (equal volumes of 0.1 M disodium hydrogen phosphate and 0.05 M ascorbic acid). Add a quarter volume of chloroform, emulsify, centrifuge at 8000 g for 10 min, collect supernatant fluid and centrifuge for 1 h at 75,000 g. Resuspend the pellets in a small quantity of the buffer. Further purify by rate zonal centrifugation at 45,000 g for 75 min in gradients of 10-40% sucrose.

Properties of Particles

In dilute solutions the virus sediments as a single component with sedimentation coefficient (s_{20, w}) of 188 S (R. D. Woods, unpublished data).A₂₆₀/A₂₈₀: 1.21.

Particle Structure

The virus has rod-shaped particles about 300 nm long and 17 nm wide. The preparations also contain shorter particles (Francki et al., 1971) (Fig.6).

Particle Composition

Nucleic acid: The particles contain c. 5% RNA.Protein: Each subunit of the coat protein of strain Adel contains about 158 amino acid residues: Ala, 14; Arg, 11; Asx, 17; Cys, 1; Glx, 16; Gly, 9; His, 1; Ile, 11; Leu, 13; Lys, 4; Met, 0; Phe, 7; Pro, 4; Ser, 14; Thr, 13; Trp, 5; Tyr, 5; Val, 13 (Francki et al., 1971). Of the other tobamoviruses whose coat proteins have been analysed, Sammons’ opuntia virus has a composition most similar to that of frangipani mosaic virus..

Relations with Cells and Tissues

In the cytoplasm of infected parenchymatous cells of D. stramonium leaves, the particles of frangipani mosaic virus aggregate as microcrystals of various shapes and sizes. Particles were not seen in mitochondria, chloroplasts or nuclei although these organelles are not of normal appearance.

References

Francki & McLean, Aust. J. biol. Sci. 21: 1311, 1968.
Francki, Zaitlin & Grivell, Aust. J. biol Sci. 24: 815, 1971.
McLean & Francki, Virology 31: 585, 1967.
Varma, Gibbs & Woods, J. gen. Virol. 8: 21, 1970.

Overwatering your Plumeria

Don’t Overwater your Plumeria

At one time or another, we all overwater our plumeria or you may live in a heavy rainfall area and had flooding problems. Overwatering, prolonged heavy rainfall, or flooding can cause havoc on your plumeria. Poor drainage can also contribute to this problem.

Anaerobic Soil

Overwatering your soil causes your soil to be waterlogged, not a healthy environment for a plumeria to live in. Much like we would not be comfortable living underwater all the time. We need to come up for air and the plumeria roots need oxygen too.

Saturated soils with poor drainage can quickly become anaerobic, making the plumeria susceptible to diseases like root rot. When plumeria roots sit in excess water for too long, they start to rot or decay. As the roots deteriorate, they can’t take up water, so the plumeria wilts.

Clues your soil or potting mix needs help

When too much water is around the roots, it is likely the beneficial microorganisms and soil life that were living in your pot and keeping your plumeria healthy have drowned or at the best case, their numbers have greatly reduced. If this is the case, the potting mix or soil may smell ‘sour’ or anaerobic. Oxygen normally fills the gaps in between the soil crumb structure and all organisms and plumerias need air to live. When plumeria roots start to decay, you may notice this unpleasant smell.

If your potted plumeria shows these tell-tale signs of overwatering, there is a problem with the soil:

Your plumeria is wilting, dropping leaves
Your plumeria is looking unwell all of a sudden
Your plumeria is being attacked by pests or disease
Worms are coming up to the surface in great numbers (they are trying to save themselves from drowning)
Sometimes you might notice a scum or residue on the surface of the soil

Here are some suggestions to help you from overwatering your plumeria:

Adding coarse mulch material to the bottom of the pot will also help drainage
Mix your soil with 50% Perlite
Use pots with many drain holes
Add more drain holes in your pot
Locate your pots in well-drained areas
Or plant in the ground, when possible

If the pot or container feels heavy and the plumeria is still wilting, the excess water may not be getting away fast enough. If you have already drilled enough holes, you may need to actually remove your plumeria from the pot to save it. Spread out a number of sheets of newspaper in a tray. Lay the pot on its side and gently slide out the plumeria’s root ball.

Allow the root ball to dry on the newspapers for about 12 hours or more, then using clean sharp scissors, trim off any dark-colored (brown rather than white) or slimy roots. When you are finished, re-pot the plumeria in a clean container with some fresh potting mix as already outlined.

Using Coarse Material in your pot:

We have found that putting an inch of two of coarse, decomposing mulch in the bottom of the pot helps with drainage and plumeria health.

Most books and websites on container gardening recommend the addition of coarse material such gravel, sand, pebbles, pottery shards, or polystyrene pieces to the bottom of pots to improve drainage, scientific studies have consistently demonstrated quite the opposite is true. According to one scientist, Dr. Chalker-Scott, Extension Horticulturalist and Associate Professor at the Washington State University:

“Nearly 100 years ago, soil scientists demonstrated that water does not move easily from layers of finer textured materials to layers of coarser textured materials. Since then, similar studies have produced the same results. The coarser the underlying material, the more difficult it is for the water to move across the material’s face. Gravitational water will not move from a fine soil texture into a coarser material until the finer soil is saturated. Since the stated goal for using coarse material in the bottoms of containers is to “keep soil from getting water logged,” it is ironic that adding this material will induce the very state it is intended to prevent.”

Resist the Urge to Overwater:

Resist the urge to water your plumeria without checking to see if they actually need water – it can actually make things worse! Waterlogging and compaction can create ideal conditions for diseases such as phytophthora and other fungal attacks.

Potted plumerias that have been inundated with water will also have likely leached out much of the plumeria food or fertilizer that was in the pot previously. You will need to replace this food source with some more organic fertilizer to ensure your plumeria has the energy it needs to regain its health.

If you notice discolored or yellowing leaves, this is often a sign your plumeria is crying out to be fed. This is because it is missing essential minerals! A slow release, powdered or pelleted fertilizer and compost can help restore the nutrients.

How to read a Fertilizer Label

How to Read a Fertilizer Label

You want to make sure your Plumeria are getting the nutrition they need, but there are so many choices when it comes to selecting fertilizer. How do you know what is really in the bag? There are certain rules that all fertilizer makers must follow when they label their products and understanding these rules can make comparing fertilizers much easier.

Major Ingredients: Most commercial fertilizers have 3 numbers on the front label, separated by dashes. For example 11-11-13. This is the fertilizer analysis or percentage by weight of the 3 major nutrients plants need: nitrogen, phosphorus, and potassium, in that order. These are abbreviated as N-P-K.

So if you purchased an 11-pound bag of fertilizer labeled 11-11-13, it would contain 11% nitrogen, 11% phosphorus, and 13% potassium. The remaining 65% could be comprised of other nutrients and filler.

1st Number = Nitrogen: The first number gives the concentration of nitrogen in the product. Nitrogen encourages foliage growth, among other benefits. An 11-11-13 fertilizer would contain 11% nitrogen by weight. So for every pound of fertilizer applied there is really only .11 pounds of nitrogen. (The 10-pound bag mentioned above would contain 1.1 lb. nitrogen.)
2nd Number = Phosphorus: The middle number refers to the concentration of phosphorous. Phosphorous contributes to many fundamental plant processes such as rooting and setting flower buds. An 11-11-13 fertilizer would contain 11% phosphorous by weight or 1.1 pounds of phosphorous. (The 10-pound bag mentioned above would contain 1.1 lb. of phosphorus.)A good reference to get an idea if your Plumeria are Deficient in Nutrients
3rd Number = Potassium: The final number states the concentration of potassium. Potassium contributes to the overall health and vigor of plants. Again, an 11-11-13 fertilizer would contain 13% potassium by weight or 1.3 pounds of potassium. (The 10-pound bag mentioned above would contain 1.3 lb. potassium.)

Complete Fertilizers: Fertilizers that contain all three major nutrients are considered complete fertilizers. There are specialized fertilizers that are called incomplete because they lack one or more major nutrients such as a fertilizer labeled 0-20-20.

Fertilizer Ratio (An easier comparison): An easier way to compare the numbers is to break them down to the fertilizer ratio or the amounts of the 3 major nutrients in relation to each other. A 5-10-5 fertilizer has a ratio of 1-2-1. This becomes important when looking for a fertilizer for a specific need. A 1-2-1 ratio is often recommended for vegetables, which need plenty of phosphorous to set fruit. 1-2-1 could be 5-10-5, 10-20-10 or any similar extrapolation.

Other Ingredients: Any additional ingredients will be listed on the side label. This may include other nutrients like calcium, magnesium, iron, micronutrients, and even the percentage of organic matter.

Organic fertilizers: Organic fertilizers must specify which nutrient(s) is organic and it must be identified as either synthetic and/or natural, by percentage. For example 20% of Nitrogen is organic (6% synthetic, 14% organic). When something is labeled “organic”, it simply means it contains carbon atoms. However, we have come to expect that organic fertilizer, like organic food, comes from natural processes and contains nothing synthetic. That tends to be the case, especially as consumers become more educated, but be sure to read the label before you make a purchase.

Tips:
If your PH is too high or too low your nutrients could be locked in the soil.

Having a soil test done before you start adding amendments will tell you what you actually need. If your soil pH is too high or too low, your plants will not be able to access some nutrients, even if they are present in the soil.
There is no one size fits all fertilizer. Fertilizer choice depends on the type of plant being grown and the soil it is being grown in.
Always follow the label instructions when using any registered garden product. Just because a little is good, it doesn’t follow that a lot is better.
You can use fewer fertilizers with high analysis numbers than with lower numbers. Five pounds of 10-20-10 would give you the same nutrient value as 10 pounds of 5-10-5.
Organic fertilizers made from natural ingredients often have lower concentrations of the three major nutrients, so you will need to use larger amounts. However, they do contain many other nutrients that feed both the plant and the soil. If you are using synthetic fertilizer, you should supplement with some type of organic matter such as compost or manure, to maintain soil health.