Home
 |
 |
Organic Field Crop Production and Marketingin North Carolina |
North Carolina Organic Grain Production Guide Chapter 4: Crop Production Management - Organic Wheat and Small Grains
Production Management Key management practices for organic wheat and small grain production:
Variety Selection As a general rule, only small grain varieties that have been successfully grown in the North Carolina Small Grain Official Variety Test for two years should be considered for production. Official Variety Test reports are available online at http://www.smallgrains.ncsu.edu or from your county Extension center. It is nearly impossible to pick a single best variety. Consequently, producers should plant two or more 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:
Planting Date 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 the most recent edition of the Small Grain Production Guide or go online to http://www.smallgrains.ncsu.edu/Guide/Chapter7.html. Rotation and Field Selection Planting wheat into old wheat stubble is always a bad idea. Several major small grain diseases and Hessian fly are vectored on old wheat stubble. Short rotations put small grains at high risk to numerous soilborne diseases and should be avoided in organic production. Additionally, as described in more detail below, the best way to avoid a Hessian fly problem is to plant at least one field (or ¼-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, wild garlic, wheat spindle streak, or wheat soilborne mosaic virus should be avoided. 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. A complete guide to seeding rate, drill calibration, planting depth, and other planting considerations can be found in the most recent edition of the Small Grain Production Guide or go online to http://www.smallgrains.ncsu.edu/Guide/Chapter6.html. Soil Fertility Wheat that yields 40 bushels per acre uses about 50 pounds of nitrogen per acre, 25 pounds of phosphate per acre, and 15 pounds of potash per acre. 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. See Chapter 6 of this guide for more information on soil fertility in organic production. In early spring, it is possible to test a wheat crop and determine how much additional nitrogen it needs to produce optimal yield. Organic growers may want to use tissue testing to determine whether the crop needs additional spring top-dress nitrogen. Weed Management 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 if needed. 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. 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. Insect Pest Management Wheat fields are susceptible to many kinds of insects. Only a few species may become pests, and even when they do, they usually do not reach damaging above-threshold numbers. However, in some seasons or under certain circumstances, insect pests of wheat can be very damaging. The following insects may become abundant enough to cause significant injury to wheat crops in North Carolina: aphids (several species), cereal leaf beetle, Hessian fly, and armyworm (sometimes called true armyworm). Other plant-feeding insects, such as grasshoppers, chinch bugs, or fall armyworms, may occasionally damage wheat. Descriptions of all these insects may be found in the most recent edition of the Small Grains Production Guide, at county Extension centers, or at the following Web sites: http://www.ces.ncsu.edu/plymouth/pubs/ent/index4.html and http://www.smallgrains.ncsu.edu/Insects/Insects.html Wheat-feeding aphidsThree primary species of aphids occur in North Carolina wheat: the English grain aphid, the bird-oat cherry aphid, and the corn leaf aphid. Aphid feeding potentially reduces yield, but usually not dramatically. Aphids are also vectors of barley yellow dwarf virus (BYDV), and this disease can be a serious concern. A complex of biological control agents accompanies aphids, including parasites, predators, and pathogens (mainly fungi). These biological control agents ordinarily exert a powerful controlling influence on aphid populations, especially in the spring, although it usually requires some time before the aphid populations “crash” due to the combined influence of these agents.Several cultural practices can help reduce the chance of aphid damage and BYDV infection in organic production:Avoid early planting. Cool weather will slow aphid feeding and activity in the newly emerged crop. Planting after the end of warm weather not only reduces the chance of crop damage due to aphid feeding, but also makes it less likely that aphid-transmitted BYDV infections will occur. The aphid population may build up again in the spring, but these populations are less damaging because plants are larger, growing more rapidly, and are more tolerant to feeding and BYDV infection.Avoid excessively high soil nitrogen levels. Aphids reproduce most rapidly on plants with high-nitrogen content. Maintaining nitrogen levels within the prescribed agronomic level (found in the most recent edition of the Small Grain Production Guide) helps to avoid high aphid populations.Select wheat varieties with BYDV resistance. If BYDV is a regular problem on your farm or on neighboring farms, a highly effective strategy is to select wheat varieties that resist this disease. A list of wheat varieties and their resistance to BYDV can be found at this Web site:http://www.smallgrains.ncsu.edu/Varieties/Varieties.htmlArmywormArmyworm moths are one of a few moths active in late winter and early spring. Armyworm caterpillars may cause serious defoliation and substantial head drop. They are most prevalent in the northeastern counties of North Carolina.Management options. 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) in emergency situations. Accepting the feeding of armyworm is not likely to result in large yield losses unless plants were defoliated early (before or during the heading period). For scouting information on armyworm, check the most recent edition of the Small Grain Production Guide or go online to http://www.smallgrains.ncsu.edu/Guide/Chapter11.html.Cereal leaf beetleThe cereal leaf beetle (CLB) has one generation each year, and both the adult and larval stages eat leaf tissue on wheat and oats. They do not feed on barley, triticale, or rye.Leaf feeding by larvae during April and May can reduce yields.Cereal leaf beetle is an introduced pest, and few native biological control agents affect adult beetles, eggs, or larvae. A few generalist predators, such as lady beetles, appear to consume cereal leaf beetle eggs and, perhaps, young larvae in early spring. The North Carolina Department of Agriculture has released several species of exotic parasites throughout the state. These parasites develop within cereal leaf beetle eggs or larvae and have the potential to keep populations below an economic level. Parasite release programs have worked well in several other states, but so far have had limited success in North Carolina.Cultural practices. Cereal leaf beetles prefer to attack a thin field full of little plants rather than a thick, lush field full of large, healthy wheat. To minimize the chances of beetle invasion, the organic producer needs to do everything possible to assure a thick, well-tillered, healthy crop. This means good seed bed preparation, planting on time, using high quality seed, correct drill calibration, and getting good soil-seed contact at the proper seeding depth. These steps will also increase the crop’s tolerance to CLB feeding.Insecticides. Insecticides approved for organic production (such as a spinosad) and labeled for cereal leaf beetle may be applied in emergency situations. For scouting information for cereal leaf beetle, check the most recent edition of the Small Grain Production Guide or go online: http://www.smallgrains. ncsu.edu/Guide/Chapter11.htm l. In addition, a special publication on this pest can be found at http://www.ext.vt.edu/pubs/entomology/444-350/444-350.html.Hessian flyIn recent years, Hessian fly infestations have caused extensive losses in many North Carolina fields. Organic farmers should use several methods to minimize Hessian fly problems.Rotation. 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, since 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.Tillage. Disking wheat stubble after harvest effectively kills the Hessian fly. Burning is not as effective as disking. Although burning wheat straw will reduce populations, many pupae will survive below the soil surface.Careful use of cover crops. 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.Plant on time. Do not delay planting until after the first freeze (often called the fly-free date) because an early freeze in North Carolina is not a dependable event. Often a “killing freeze” does not occur until December in many areas of North Carolina, which is later than most growers need to have wheat planted for agronomic purposes. Organic producers throughout North Carolina should also avoid planting before the recommended planting dates.Resistant varieties. Many wheat varieties are advertised as having Hessian fly resistance. To be effective in North Carolina, however, wheat varieties must be specifically resistant to Hessian fly biotype-L. A list of wheat varieties with biotype-L resistance can be found on the Internet at http://www.smallgrains.ncsu.edu/ or through county Extension offices. For more information on Hessian Fly, see The Hessian Fly: A Pest of Wheat in North Carolina (AG-368), which is available online: http://www.ces.ncsu.edu/depts/ent/notes/Grain/Hessian/HflyAG-368.html.Disease Management Disease identificationThe first step in solving disease problems is to identify the disease. Excellent small grain disease information and assistance with disease identification can be found in the latest edition of the Small Grains Production Guide or on the Web at http://www.smallgrains.ncsu.edu/Diseases/Diseases.html. Varieties are rated for disease resistance at http://www.smallgrains.ncsu.edu/Varieties/Varieties.html.Barley yellow dwarf virusBarley yellow dwarf virus (BYDV) is the most important viral disease of wheat, oats, barley, and rye in this state. The virus is transmitted by aphids that over-summered on nearby corn crops or host grasses. The best control measure in organic production is to plant varieties that are resistant to this disease.Powdery mildewOne of the most yield-limiting factors in North Carolina wheat production is powdery mildew. This is especially true in the coastal plain, the 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.Select resistant varieties. The best protection against powdery mildew is to select wheat varieties that are resistant to it. Organic producers who want high-yielding wheat must plant powdery-mildew-resistant varieties. Wheat varieties grown in North Carolina are evaluated for disease resistance every year, and new disease-resistance ratings are published in the Small Grains Official Variety Test Results and posted on the Internet every July in time for growers to order the best varieties for the next year’s production. Organic producers should check the Web site http://www.smallgrains.ncsu.edu/Varieties/Varieties.html every year (or contact their county Extension agent for the information), and use the list of the most resistant varieties as a starting point for ordering seed.Adjust planting date. 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, especially those in the coastal plain, southern piedmont, and tidewater region, should also avoid planting before the recommended planting dates.Leaf rustLeaf rust is a foliar disease that attacks wheat late in the growing season. While leaf rust can occur anywhere in North Carolina, it is most likely to be a problem in the 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 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 smutLoose smut symptoms occur between heading and maturity. Infected seed appears 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. Therefore, using certified seed is a highly effective way to avoid loose smut. Organic farmers who use saved seed should never plant seed from a crop infected with loose smut.Septoria leaf and glume blotchSeptoria leaf and glume blotch may occur at any time during the growth of the plant and on any portion of the plant. Rotation away from small grains for at least three years can lessen the severity of septoria. Plowing under wheat stubble will prevent infection from the previous wheat crop. Potash, copper, and magnesium should be kept at recommended levels. In some cases, septoria can be seedborne, so certified seed can reduce introduction of the disease. Organic farmers should never save seed for planting if the wheat was infected with septoria.Scab or head blightScab, a fungus that is seen as prematurely bleached heads or spikelets, can occur in all small grains. Of the small grains, wheat and barley are the most susceptible to this disease, and rye and triticale are the most resistant. Scab occurs and is spread to small grains in the spring. It also results in toxins (vomitoxin is most common) in the harvested grain.The first line of defense against scab is to plant wheat varieties with resistance to the fungus. A complete list of wheat varieties and their resistance to head scab can be found at http://www.smallgrains.ncsu.edu or at county Extension centers. Wheat producers with a history of scab should seriously consider selecting varieties based on this information. Tillage practices that bury wheat or corn residues and rotations of at least three years are effective means of controlling scab in organic production. Planting several wheat varieties with different heading dates will stagger head emergence and flowering through the spring and reduce the chance that environmental conditions will be suitable to scab in all wheat fields.If scab is present, the combine may be adjusted so that the lightweight diseased grain is removed along with the chaff. This will not remove all the infected grain, but can help reduce mycotoxin levels in the grain going to market. Organic farmers should never use saved seed if head scab was present in the crop that produced the seed.Other small grain diseasesSeveral other small grain diseases can be problems in North Carolina. Growers in need of more detailed information should check online at http://www.smallgrains.ncsu.edu or with their county Extension agent.Avoiding Spring Freeze Injury Late spring freeze damage is a major factor in reducing yields of North Carolina wheat. “Heading date” is an important indication of how susceptible a variety will be to late spring freeze damage. Early-heading varieties are the most susceptible to freeze damage. Medium- and late-heading varieties are more likely to avoid spring freeze damage, and they generally produce higher yields than early- or medium-early heading varieties. Heading date also indicates the best planting date for a wheat variety. Medium- and late-heading wheat varieties tend to do best when planted at the start of the planting season, and should be the first varieties planted. Early and medium-early varieties tend to produce the highest yields when planted later in the fall. Wheat variety heading date information can be found online: http://www.smallgrains.ncsu.edu/Varieties/Varieties.html. |