Key management practices for organic wheat and small grain production:
- 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 NC is the Wheat Variety Performance and Recommendations, which is released every July at NC State University and prepared by Randy Weisz (in the Crop Science Department) and Christina Cowger (USDA–Agricultural Research Service, Plant Pathology Department). This newsletter is based on the Official Variety Test Report and additional Cooperative Extension variety testing projects around North Carolina. As a general rule, only wheat varieties that are reported in this newsletter should be considered for production.
It is nearly impossible to pick a single best variety. Consequently, producers should plant at least two varieties every season to reduce their risks and maximize the potential for a high-yielding crop. The following are general guidelines for selecting varieties for organic wheat production:
- Check the Wheat Variety Performance and Recommendations for a list of varieties tested for at least two years.
- The two disease and pest problems with the greatest potential to completely devastate a small-grain crop in any part of North Carolina are Fusarium sp. head blight (scab) and Hessian fly. Choose only varieties that are rated as moderately
- resistant (MR) to scab. Avoid varieties rated “poor” for Hessian fly biotype-L, especially if planting will be early or even on time.
- To avoid spring freeze injury, avoid earlyheading varieties in favor of medium- and late-heading varieties.
- If you are in the NC piedmont, choose varieties with resistance to barley yellow dwarf virus (BYDF).
- If you are in the NC coastal plain, ideal varieties will have resistance to powdery mildew, leaf rust, and soilborne mosaic virus.
- If you are in the NC tidewater, choose varieties with resistance to leaf rust and soilborne mosaic virus.
- If wheat is being produced for the baking industry, it is a good idea to check variety selection with the end user.
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 summer over 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 1⁄4-mile) away from last year’s wheat stubble and 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 ever 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 are present 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, and a field known to have one or both viruses should be either planted with an appropriately resistant variety (see the Wheat Variety Performance and Recommendations SmartGrains Newsletter) or removed from small-grain production.
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 1 in the Wheat Variety Performance and Recommendations SmartGrains Newsletter. 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.
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 (like a Dyna-Drive) that allows tillage to a specified depth. Because plant establishment potential is reduced and seed placement is not uniform, seeding rates should be increased for broadcast seeding. Increase broadcast seeding rates by 30 percent 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 lb of phosphate per acre (most of which is removed with the grain) and about 135 lb of potash per acre (of which about 100 lb 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 lb of nitrogen per acre. See Chapter 6 of this guide (pp. 25 – 31) 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 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. 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 1 in the Wheat Variety Performance and Recommendations SmartGrains Newsletter. 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 7 for more information on weed management in organic production systems.
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 in the Small Grain Production Guide. 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 BYDV. Aphid populations are usually kept in check by weather conditions (such as freezing temperatures in late fall) and biological control agents, such as 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 1, Wheat Variety Performance and Recommendations SmartGrains Newsletter) 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 Performance and Recommendations SmartGrains Newsletter).
Armyworm 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 pre-plant 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. Although 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 NC 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 doublecropped 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 ¼-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 1, Wheat Variety Performance and Recommendations SmartGrains Newsletter.
If Hessian fly pressure is anticipated, selection of wheat varieties resistant to Hessian fly biotype-L is a good idea (see the Wheat Variety Performance and Recommendations SmartGrains Newsletter).
The best disease management tactic for organic producers is to avoid diseases in the first place by selecting wheat varieties with good resistance packages. Excellent small grain disease information and assistance with disease identification can be found in Small Grain Disease Management in the Small Grain Production Guide. 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 1, Wheat Variety Performance and Recommendations SmartGrains Newsletter) is a good way to avoid 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 Performance and Recommendations SmartGrains Newsletter). Avoid planting into unincorporated light-colored residues of corn or other crops, as these attract aphids.
One of the most yield-limiting factors in NC wheat production is powdery mildew. This is especially true in the NC coastal plain and southern piedmont and some NC 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. 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 1, Wheat Variety Performance and Recommendations SmartGrains Newsletter).
Leaf rust is a foliar disease that attacks wheat late in the growing season. Although leaf rust can occur anywhere in North Carolina, it is most likely to be a problem in the NC coastal plain and tidewater. Conventional producers rely on foliar fungicides to protect the crop from this disease. Organic producers must select varieties with good resistance to leaf rust. Organic producers, especially those in the NC tidewater, should try to select varieties that have a combination of powdery mildew and leaf rust resistance. 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 seeds appear normal. The fungus, which is found inside the embryo of the seed, 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. So 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 Stagonospora nodorum and can be a serious disease of wheat. It used to be known as septoria leaf blotch 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.
Potash, copper, and magnesium should be kept at recommended levels.
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 shouldhelp minimize SNB. Organic farmers should never save seed for planting if the wheat crop had a serious SNB epidemic.
Wheat variety resistance is also a good way to minimize this disease (see the Wheat Variety Performance and Recommendations SmartGrains Newsletter).
Scab or head blight
Head scab of small grains is 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 to other spikelets, resulting in heads that are partly green and partly bleached. Superficial pink or orange spore masses can be seen on infected spikelets. Early infections can cause kernel abortions, and later infections can cause shriveled kernels (called 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 even for swine feed. 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 to 86°F) before and during flowering also favor scab. Sadly, no single management practice will defeat scab. Wheat producers who take the following measures, however, will reduce the likelihood of a major scab problem:
Many wheat varieties have moderate scab resistance. The best source for wheat variety resistance to scab is theWheat Variety Performance and Recommendations SmartGrains Newsletter. There are also a few barley varieties with some scab resistance (such as Thoroughbred from Virginia Tech).
Spring weather is often not warm and moist 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), adjust the combine 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.
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 University Plant Disease & 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’s fine to bend them double. For instructions and a submission form, contact the NC State University Plant Disease & Insect Clinic via the web 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: Feb. 10, 2014
Other Publications in North Carolina Organic Grain Production Guide
- Chapter 1: Introduction
- Chapter 2: Organic Crop Production Systems
- Chapter 3: Crop Production Management - Corn
- Chapter 4: Crop Production Management - Organic Wheat and Small Grains
- Chapter 5: Crop Production Management - Organic Soybeans
- Chapter 6: Soil Management
- Chapter 7: Weed Management
- Chapter 8: Rolled Cover Crop Mulches for Organic Corn and Soybean Production
- Organic Certification for Field Crops: A Guide
- Chapter 10: Marketing Organic Grain Crops and Budgets
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