Key Management Practices
- Implement crop rotation.
- Bury crop residues with tillage, if possible.
- Choose varieties with resistance to disease and insect pests.
- Plant on time (not too early, not too late) in a well-prepared seedbed.
- Use correct seeding rates, drill calibration, and drill operation.
- Avoid excessively high nitrogen levels (but work towards good soil fertility).
- Harvest on time. Don’t let mature grain stand in the field.
The best source of unbiased wheat variety performance information for North Carolina is Wheat Variety Disease Packages, which is updated every August at NC State University. The ratings are done by Paul Murphy (Crop and Soil Sciences) and Christina Cowger (USDA–Agricultural Research Service, Entomology and Plant Pathology). The ratings reflect the genetic characteristics of varieties rather than the effects of seed treatments.
- The disease that can devastate a small grain crop in any part of North Carolina is Fusarium head blight (scab). Choose only varieties that are rated moderately resistant (MR) to scab. Also, Hessian fly can cause massive losses in the coastal plain and tidewater. Avoid varieties rated “S” (susceptible) to Hessian fly biotype-L, especially if planting will be early or even on time.
- In addition, the following recommendations apply:
- If you are in the North Carolina coastal plain, ideal varieties will have resistance to powdery mildew and leaf rust.
- If you are in the North Carolina tidewater, choose varieties with resistance to leaf rust.
- To avoid spring freeze injury, avoid early-heading varieties in favor of medium- and late-heading varieties.
- If wheat is being produced for the baking industry, it is a good idea to check variety selection with the end user.
Not too early and not too late! Planting too early puts the crop at severe risk for powdery mildew, Hessian fly, aphids, and barley yellow dwarf virus. Planting too late will reduce yields, increase the risk of having a winter annual weed problem, and result in thin stands that will attract cereal leaf beetles. For the optimum planting times for your region, see “Small Grain Planting Dates” in the Small Grain Production Guide.
Rotation and Field Selection
Planting wheat into old wheat stubble is always a bad idea. Several major small grain diseases (Stagonospora nodorum blotch, tan spot, and scab) are transmitted by old wheat stubble. Short small grain rotations also put the crop at high risk to soilborne diseases such as take-all. Clearly, wheat two years in a row is a bad idea.
Hessian fly pupae oversummer in wheat residues, so planting into or even near old wheat stubble is a good way to get a Hessian fly infestation in a new wheat crop. The best way to avoid a Hessian fly problem is to plant at least one field (or one-fourth mile) away from last year’s wheat stubble, and to avoid planting near an early-planted wheat cover crop.
Fields with a history of italian ryegrass or wild garlic should be avoided because there are no good organic methods for controlling these weeds.
Finally, fields in which infections by soilborne mosaic virus or wheat spindle-streak mosaic virus have been identified require special consideration. These two viruses are vectored by a soil dwelling microorganism. Of the two viruses, soilborne mosaic virus is the more damaging to yield. Once the virus and microorganism occur in a field, there are no practical ways to eliminate them. There are excellent wheat varieties that have resistance to one or both of these diseases. A field known to have one or both viruses should either be planted with an appropriately resistant variety (see the Wheat Variety Disease Packages) or removed from small grain production.
Seeding Rate, Drill Calibration and Operation
A good stand of wheat is the best defense against weeds and cereal leaf beetle and is the best indicator of a high yield potential. When planting on time with high quality seed into conventionally tilled seedbeds, the target seeding rate is 30 to 35 seeds per square foot. Increase this target rate if seed germination is below 90 percent or if planting is more than two weeks after the dates shown in Figure 4-1. A complete guide to seeding rate, drill calibration, planting depth, and other planting considerations can be found in “Small Grain Seeding Rates for North Carolina” in the Small Grain Production Guide.
Special Considerations for Broadcast Seeding
Broadcast seeding often results in uneven seed placement in the soil, which results in uneven emergence and stands. Seeds may be placed as deep as 3 to 4 inches, where many seeds will germinate but will not emerge through the soil surface. Other seeds may be placed very shallow or on the soil surface. These seeds often do not survive due to dry soil or winter damage. The uneven stands from broadcasting often result in lower yields compared with drilling. Uneven seed depth and reduced yields are especially problematic when incorporation is done with a disk. Most growers who have been successful with broadcast seeding use a special implement (such as a Dyna-Drive) that allows tillage to a specified depth. Because plant establishment potential is reduced when seed placement is not uniform, seeding rates should be increased for broadcast seeding. Increase broadcast seeding rates by 30 to 35 percent over drilled seeding rates.
Soil pH is very important for a high-yielding wheat crop. Low soil pH can result in poor growth and development. High soil pH, especially on coarse-textured soils, can result in manganese deficiencies. Wheat that yields 65 bushels per acre takes up about 45 pounds of phosphate per acre (most of which is removed with the grain) and about 135 pounds of potash per acre (much of which—about 100 pounds—is in the straw). Wheat is a moderately heavy feeder, but not as heavy as corn. For best yield results, an organically approved nitrogen source (such as manure, compost, or a tilled-in legume) should be added at or before planting and again in the spring. A wheat crop yielding 65 bushels per acre will take up about 70 pounds of nitrogen per acre. See chapter 9 of this guide, “Soil Management,” for more information on soil fertility in organic production. Some organic farms are demonstrating large N carryover and may not need any spring nitrogen. Unfortunately, no soil test exists that will predict how much nitrogen carryover to expect. In early spring, it is possible to tissue test a wheat crop and determine how much additional nitrogen, if any, is needed to produce an optimal yield. Information about how to use this tissue test can be found in “Nitrogen Management for Small Grains” in the Small Grain Production Guide. The application window for spring N is very narrow, and the source of fertility affects whether the nitrogen will be released in time to maximize yield. For manure sources, only the ammonium fraction should be considered available in time. This fraction is labeled “Ammonium NH4+-N” on the waste analysis reports from the NC Department of Agriculture and Consumer Services (NCDA&CS). Some of the slower releasing forms of nitrogen in the manure may be available during grain fill when protein content is set.
Essentially all weed control in organic wheat must be achieved in seedbed preparation before planting. Little to no cultivation is used in wheat after planting to kill emerging weeds, but a rotary hoe or tine weeder can be used before the crop emerges and again at the one-to-three-leaf stage. However, weeds usually cause fewer problems in wheat than in corn or soybeans because wheat is a strong competitor against weeds and is drilled in narrow rows that quickly shade the soil. This is especially true of wheat that is planted near the dates shown in Figure 4-1. Most wheat drills are set to plant rows that are 6 to 8 inches apart. Organic producers may want to take advantage of row spacing as narrow as 4 inches to help the wheat outcompete winter annual weeds. Avoid planting organic wheat in fields with italian ryegrass or wild garlic problems as these weeds can lead to quality problems in the harvested grain. Also, use caution with hairy vetch as a cover crop in fields where wheat will be planted because hairy vetch that reseeds can contaminate wheat grain with seeds that are similar in size and weight and that are difficult to separate. See Chapter 10: Weed Management, for more information on weed management in organic production systems.
Insect Pest Management
Many kinds of insects can be found in wheat fields, but only a few are likely to become yield threatening. A detailed description of small grain insect pests and their management can be found in Insect Pest Management for Small Grains. Organic producers should take note of the following potential insect pests.
Aphids are small sucking insects that colonize small grains early in the season and may build up in the spring or fall. They injure the plants by sucking sap or by transmitting barley yellow dwarf virus (BYDV). Aphid populations are usually kept in check by weather conditions (such as freezing temperatures in late fall) and biological control agents, including lady beetles, parasitic wasps, syrphid fly maggots, and fungal pathogens, which are often abundant in small grains. Consequently, direct yield reductions due only to aphid feeding are rare. On the other hand, BYDV can be a serious problem, especially when it is transmitted to wheat plants in the fall. Because cold temperatures kill aphids, planting near or after the first freeze (see Figure 4-1) is a good way to avoid early aphid feeding and BYDV infections. If BYDV has been a problem in the past, selecting wheat varieties that are resistant to it may also be valuable (see the Wheat Variety Disease Packages).
Armyworms infests small grains, usually wheat, from late April to mid-May. They can cause serious defoliation, injury to the flag leaf, and head drop. Few cultural management options are available for armyworm. Organic growers have the choice of accepting the feeding of armyworms or using an insecticide approved for organic production (such as a spinosad or pyrethrin) in emergency situations.
Cereal leaf beetle
The cereal leaf beetle has one generation each year, and both the adult and larval stages eat leaf tissue on wheat and oats. They also feed on barley, triticale, or rye. Leaf feeding by larvae during April and May can reduce yields. Cereal leaf beetle adults are attracted to poorly-tillered wheat fields. Management practices that lead to densely-tillered stands by mid-February can help to reduce the risk of having a cereal leaf beetle infestation. These practices include planting on time, using high-quality seed planted at recommended seeding rates, making sure that preplant fertility is adequate for rapid fall growth, and applying a split nitrogen application in February and March if additional tillering is needed in the spring. Insecticides approved for organic production (such as a spinosad or pyrethrin) and labeled for cereal leaf beetle may be applied in emergency situations. However, while spinosad will provide adequate control of light infestations, it will not provide adequate control when cereal leaf beetle populations are high.
In recent years, numerous North Carolina fields have suffered extensive losses because of Hessian fly infestations. Historically a wheat pest in the Midwest, changes in field-crop production including early-planted cover crop wheat, increased adoption of no-tillage double-cropped soybeans, and the use of wheat as a cover crop for strip-tillage cotton and peanut production have permitted the Hessian fly to reach major pest status in North Carolina. Organic farmers should use several methods to minimize Hessian fly problems.
- Because the Hessian fly life cycle depends largely upon the presence of wheat stubble, using rotations that do not plant new wheat into or near a previous wheat crop’s stubble will be the most effective way to prevent infestations. Additionally, because the Hessian fly is a weak flier, putting at least one field (or about one-fourth mile) between new wheat plantings and the previous season’s wheat fields can be a successful method of preventing new infestations.
- Disking wheat stubble after harvest effectively kills Hessian fly. Burning is not as effective as disking. Although burning wheat straw will reduce populations, many pupae will survive below the soil surface.
- Serious Hessian fly infestations have occurred in areas where wheat for grain was planted near early-planted wheat for cover or early-planted wheat for dove hunting purposes. In organic systems using cover crops, selecting a small grain other than wheat will reduce Hessian fly populations. Oats, rye, and triticale are not favorable for Hessian fly reproduction and do not serve as a nursery.
- In many wheat-producing regions a “fly-free date” has been established to guide growers in planting after the first freeze has killed the Hessian fly adults. This approach has not worked in North Carolina because our first freeze is highly unpredictable and may not even happen until it is too late to plant. Instead, it is a good idea to plant wheat on or after the dates in Figure 4-1.
- If Hessian fly pressure is anticipated, selection of wheat varieties resistant to Hessian fly biotype-L is a good idea (see the Wheat Variety Disease Packages).
The best disease management tactic for organic producers is to avoid diseases in the first place by selecting wheat varieties with good resistance packages. Table 4-1 contains a list of commercially available wheat varieties and their disease ratings based on screening data within the past three years. When planning for an organic small grain crop, variety selection and cultural practices should include consideration of the following diseases.
Barley yellow dwarf virus
Because cold temperatures kill the aphids that vector BYDV in the fall, planting near or after the first freeze (see Figure 4-1) is a good way to avoid BYDV infections. Avoid planting into unincorporated light-colored residues of corn or other crops, as these attract aphids.
One of the most yield-limiting factors in North Carolina wheat production is powdery mildew. This is especially true in North Carolina’s coastal plain, southern piedmont, and some tidewater areas. Conventional producers often do not consider powdery mildew in their planning because they can rely on foliar fungicides to control the disease if it occurs. Organic producers do not have that luxury.
- The best protection against powdery mildew is to select wheat varieties that are resistant to it. Organic producers in the NC coastal plain who want high-yielding wheat must plant mildew-resistant varieties. Variety resistance to powdery mildew may break down from year to year, so organic producers should check the most recent variety ratings every year before ordering seed.
- A second defense against powdery mildew is to plant after the weather has turned cold. This decision involves a trade-off. Although powdery mildew does not grow in cold weather, neither does wheat. This means that late-planted wheat may avoid powdery mildew, but it is also likely to suffer from lower yields and attack by cereal leaf beetle. However, organic producers should also avoid planting before the recommended planting dates (Figure 4-1).
Leaf rust is a foliar disease that attacks wheat late in the growing season; some leaf rust can therefore be tolerated. While leaf rust can occur anywhere in North Carolina, it is most likely to be a problem in the coastal plain and tidewater. Conventional producers rely on foliar fungicides to protect the crop from this disease. Organic producers must select varieties with at least some resistance to leaf rust (rating of moderately susceptible, moderately resistant, or resistant). Organic producers, especially those in the coastal plain, should try to select varieties that have a combination of powdery mildew and leaf rust resistance. As with powdery mildew, variety resistance to leaf rust also deteriorates from year to year, so organic producers should check the most recent variety ratings every year before ordering seed.
Loose smut symptoms occur between heading and maturity. Infected seed appears normal. The fungus, which is found inside the seed’s embryo, will grow within the plant from germination until the seed heads emerge and smutted grains appear. Therefore, symptoms from an infection that occurs in one year will not be seen until plants from the infected seed mature in another year. Because loose smut is seedborne, control measures focus on the seed to be planted. Certified seed fields are inspected for loose smut, and strict standards are enforced. Seed from fields with loose smut are rejected. Therefore, using certified seed is a highly effective way to avoid loose smut. Organic producers who use farmer-saved seed should never plant seed from a crop infected with loose smut.
Stagonospora nodorum blotch
Stagonospora nodorum blotch (SNB) is caused by the fungus Parastagonospora nodorum and can be a serious disease of wheat. It used to be called “septoria leaf and glume blotch.” Symptoms may occur at any time during the plant’s growth and on any portion of the plant.
- Because wheat residues harbor the fungus, unincorporated residues can produce a severe SNB epidemic if fungal spores are splashed up onto the new crop. This puts no-till planted wheat that follows directly behind double-cropped soybeans at higher risk of an SNB epidemic. Conversely, plowing under wheat stubble will eliminate residue as a source of infection.
- When SNB gets onto the developing grain head, the grain may be infected. If this grain is planted, the seedlings may be infected with SNB. Consequently, SNB can be seedborne. Using certified seed should help minimize SNB. Organic farmers should never save seed for planting if the wheat crop had a serious SNB epidemic.
Fusarium head blight (scab)
In the U.S., Fusarium head blight (FHB or head scab) of small grains is mainly caused by the fungus Fusarium graminearum, which also infects corn. Scab can occur in all small grains. Wheat and barley are the most susceptible to the disease, oats are a little less susceptible, and rye and triticale are the most resistant. Infection occurs at or soon after flowering, when fungal spores reach small grain heads by wind or rain-splash. Once it’s established in a spikelet, the fungus can spread through the rachis, or central stem of the head, to other spikelets, resulting in heads that are partly green and partly blighted, or bleached. Superficial pink or orange spore masses can sometimes be seen on infected spikelets. Early infections can cause kernel abortions, and later infections can cause shriveled kernels (“tombstones”) that have low test weight. Scab produces toxins in the harvested grain, the most common being DON (deoxynivalenol, or vomitoxin). When DON reaches 2 parts per million (ppm), the grain is no longer fit for human consumption and cannot be sold to a flour mill. When DON reaches 5 ppm, the grain is no longer fit for swine feed; feed for poultry and cows has a higher DON tolerance. Wet weather before, during, and soon after small grain flowering is the main factor determining whether there is a severe head scab epidemic. Warm temperatures (59°F to 86°F) before and during flowering also favor scab. Sadly, no single management practice will defeat scab. However, wheat producers who take the following measures will reduce the likelihood of a major scab problem:
- Many wheat varieties have moderate scab resistance (Table 4-1). There are also a few barley varieties with moderate scab and DON resistance (such as Endeavor, LCS Calypso, SU Mateo, and Violetta).
- Spring weather is often not warm and wet for more than a week or two, so scab risk can be reduced by planting at least two wheat varieties from different heading-date classes (for example, one medium variety and one late variety). In that way, head emergence and flowering will be staggered through the spring, reducing the chance that environmental conditions will be conducive to scab in all wheat fields. A second way to force wheat to flower at different times in the spring is to stagger planting dates.
- Scout for scab before grain heads turn golden, when the contrast between the bleached and green parts of heads is still apparent. If scab is severe (more than 10 percent of heads have scab), increase the combine fan speed so that the lightweight diseased grain is blown out the back along with the chaff. This will not remove all the infected grain but can help reduce mycotoxin levels in grain heading to market.
The Mid-Atlantic states experience a significant wheat stripe rust epidemic only in about one out of four or five years. Stripe rust is caused by the fungus Puccinia striiformis, which does not appear to overwinter here, so spores generally must blow in from points south and west. Severe stripe rust epidemics usually start earlier than leaf rust, however, and the disease multiplies quickly, so it can be devastating to a susceptible variety. For an organic producer, variety resistance is the only line of defense. Variety ratings are given in Table 4-1 and at the Wheat Variety Disease Package website.
|Wheat variety||Fusarium head blight||Powdery mildew||Leaf rust||Stripe rust||Hessian fly|
|R = resistant, MR = moderately resistant, MS = moderately susceptible, S = susceptible, I = intermediate|
|AGSouth Genetics AGS 2024||S||R||R||MR||I|
|AG South Genetics AGS 2033||MR||R|
|AG South Genetics AGS 2038||MR||R||R||MS|
|AG South Genetics AGS 2055||MS||MS|
|CROPLAN SS 8530||MR||R|
|CROPLAN SRW 8550||MR||MR|
|CROPLAN SRW 9415||S||S||R|
|CROPLAN SRW 9606||S||MS|
|Harvey's AP 1871||MS||S||S||R||R|
|Harvey's AP 1882||MR||MR||MR||MR||R|
|Harvey's AP 1933||MR|
|Harvey's AP 1947||S||MR|
|Harvey's AP 1950||S|
|Limagrain LCS Panther||MR|
|Limagrain LCS 4343||MR||MR||R|
|Mid-Atlantic Seeds MAS #6||MR|
|Mid-Atlantic Seeds MAS #67||MS|
|Mid-Atlantic Seeds MAS #7||MR||MR|
|Progeny Ag P243||S||MS||MR||S|
|Progeny Ag P357||MS||MS||S||R|
|Progeny P 870||S||MS||MS||R|
|Southern Harvest SH 555||S||R||R||MR||S|
|Southern Harvest SH 4300||MS||S||S||S|
|Southern Harvest SH 4400||MS||MS||MS||MR|
|Southern Harvest SH 5550||S|
|Southern Harvest SH 7200||MS||MR||R|
|Southern Harvest SH 7510||MS|
|Syngenta SY 547||MS|
|Syngenta SY Harrison||MR||S||S||R||I|
|Syngenta SY Miskin||S|
|Syngenta SY Viper||MS||MR||MS||R||I|
|Tidewater TWS 2616||S|
|UniSouth Genetics USG 3118||MS|
|UniSouth Genetics USG 3197||MR||MR||MS||I|
|UniSouth Genetics USG 3201||S||MS||MS||R||S|
|UniSouth Genetics USG 3228||MR||MS|
|UniSouth Genetics USG 3251||S||MS||MS||MR||S|
|UniSouth Genetics USG 3316||S||S||MS||I|
|UniSouth Genetics USG 3329||MS|
|UniSouth Genetics USG 3404||S||MS||MS||R||I|
|UniSouth Genetics USG 3429||MR|
|UniSouth Genetics USG 3458||S|
|UniSouth Genetics USG 3523||MS||S||R||R|
|UniSouth Genetics USG 3536||MR||MR|
|UniSouth Genetics USG 3612||MS||MS||MS||R||S|
|UniSouth Genetics USG 3756||MR||MS||MS||MS||I|
|UniSouth Genetics USG 3833||MS||S||S||R||S|
|UniSouth Genetics USG 3895||S||S||R||R||S|
Diagnoses and Assistance From the Plant Disease and Insect Clinic
If you have a question about whether a small grain problem is caused by a disease, an insect, or something else, send a sample to the NC State Plant Disease and Insect Clinic for diagnosis. Send whole affected plants with intact roots surrounded by moist soil. Place a plastic bag around the roots to ensure they remain moist. If the plants are tall, it is fine to bend them double. For instructions and a submission form, contact the NC State Plant Disease & Insect Clinic or by phone or mail:
Plant Disease and Insect Clinic
NC State University
Campus Box 7211
1227 Gardner Hall, 100 Derieux Place
Raleigh, NC 27695-7211
For disease problems: 919.515.3619
For insect problems: 919.515.9530
Publication date: June 24, 2019
Other Publications in North Carolina Organic Commodities Production Guide
- Chapter 1: Introduction
- Chapter 2: Organic Crop Production Systems
- Chapter 3: Crop Production Management - Corn
- Chapter 4: Crop Production Management - Wheat and Small Grains
- Chapter 5: Crop Production Management - Organic Soybeans
- Chapter 6: Crop Production Management - Flue-Cured Tobacco
- Chapter 7: Crop Production Management - Peanuts
- Chapter 8: Crop Production Management - Sweetpotatoes
- Chapter 9: Soil Management
- Chapter 10: Weed Management
- Chapter 11: Rolled Cover Crop Mulches for Organic Corn and Soybean Production
- Chapter 12: Organic Certification
- Chapter 13: Marketing Organic Grain Crops and Budgets
- Chapter 14: Organic Market Outlook and Budgets
- Chapter 15: Resources for More Information on Organic Commodity Production
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