Key Management Practices
- Choose varieties that perform well in your area (selecting earlier or midseason maturity groups, if possible).
- Plant on time (not too late).
- Adjust equipment for a high plant population.
- Rotate crops.
Choosing a soybean variety also means choosing a Maturity Group. Extremely early-maturing soybean varieties, Groups III and IV, avoid pests such as corn earworm, but make weed management more difficult. These maturity groups begin to lose leaves when summer weeds can still grow. Group V or later soybeans can also be left unharvested until a killing frost defoliates weeds if weed control has been an issue. In the North Carolina coastal plain, a Group V or VI (or an earlier planting) will help avoid corn earworm (CEW) infestation during flowering. CEW is seldom a problem in the North Carolina piedmont. Variety selection is also an excellent way to deal with nematode problems. Selecting varieties that are resistant to the species and race of nematode present in the field can limit the yield loss caused by these pests. It is also a good idea to choose at least two different varieties to spread out the seasonal workload and risk. The Official Variety Test Report available online or through your county Extension Center is a good source of information on varieties. Unfortunately, there are fewer and fewer conventional or nontransgenic varieties available on the market. Organic farmers must be aware that transgenic beans are not allowed in certified organic production and choose alternate varieties.
Planting date and variety (or maturity group) selection go hand in hand. The key is to match planting date and variety maturity to the soil so that the row middles are lapped with soybean plants about 3 feet tall by flowering time. Planting earlier or planting a later-maturing variety can improve the likelihood of achieving this. In an organic farming system, avoiding pest problems is an important management technique. Planting early (by the end of May) with an early to midseason variety can help the crop avoid insect and disease problems. Double-cropped soybeans, generally planted in mid-June, require the use of Group VI or VII to obtain sufficiently large plants by flowering.
The average row width in organic soybeans in North Carolina is 30 inches but can be up to 38 inches and as low as 20 inches. Narrow-row soybeans lap row middles sooner, reducing the need for weed control. While narrow-row soybeans will compete more effectively with weeds, row spacing should not be so narrow as to prevent between-row cultivation.
Maximum soybean yield potential is achieved once a soybean canopy has lapped the row middles and reached a height of at least 3 feet before flowering. In conventional production this can be consistently achieved with plant densities of 100,000 plants per acre. However, this population recommendation is for production where herbicides are used and there is minimal to no weed competition. In contrast to conventional soybean production, weed control is the largest challenge for organic soybean production, and higher soybean seeding rates is one tactic that can improve weed control. A higher soybean plant population produces a thicker soybean canopy early in the season when weed control is critical. A seeding rate as high as 225,000 seed per acre for organic soybean results in better weed control, higher yield, and the highest economic return compared to seeding rates of 175,000. 125,000. and 75,000 seeds per acre. Lodging can become a concern with rates higher than 200,000 seeds per acre with some varieties. Furthermore, while soybean disease management is less of a concern compared to weed management, a thick plant stand will trap moisture in the canopy, which creates a favorable environment for many diseases. Higher populations in organic soybean production are also recommended when blind or broadcast cultivation (from implements like the rotary hoe or flex-tine harrow) is in use. These secondary tillage implements pass over the crop rows, often reducing the plant stand by 10 to 20 percent.
Seeding rate will depend on the planter capability, seed germination, and soil condition. Proper calibration of the planter is important, as well as planting in ideal soil conditions (the soil should be warm and moist, but not wet). If planting in June, increase these seeding rates by 20 percent.
Soybeans yielding 50 bushels per acre will remove about 188 pounds of nitrogen per acre, 41 pounds of phosphate per acre, and 74 pounds of potash per acre from the soil. However, manure and compost applications are usually unnecessary because soybeans are nitrogen-fixing legumes and the crop can make use of any nutrients applied to, but not removed by, previous crops. If soybeans were not grown in previous years, soybeans should be inoculated with species of Bradyrhizobium bacteria specific for soybeans. See Chapter 9: Soil Management for more information.
Organic weed management is more challenging in soybeans than in corn because the soybean foliage does not generally overlap and shade the row middles until later in the season. Generally, narrow rows (down to 20 inches) and increased plant population can help the crop compete more effectively against weeds. When managing weeds in soybeans, consider also that different planting times for soybeans result in the plants competing against different sets of weed species. Weeds that emerge during the first four to five weeks after planting will cause the most damage in terms of yield reductions. Weeds that emerge after this time will have little effect on yield, although they may make harvest more difficult and will set seed. The goal should be to keep the field clean through the first four to five weeks after planting. Clean cultivation is used on most organic soybean acreage in the state. A blind cultivator, such as a flex-tine harrow or rotary hoe, is used before soybean emergence and approximately every five days afterwards. Anywhere from two to five blind cultivations occur before between-row cultivation begins. A frequent problem is the missing of blind cultivations due to wet weather. Unfortunately, near-row weeds missed during this wet weather often remain until the end of the season. Taller crops, such as corn, can endure lots of soil throwing, and between-row cultivators can be set to bury young weeds. However, soybeans can tolerate only small amounts of burial due to how low pods are set on stems. One tactic is to plant to moisture when the weather forecast is clear so that at least one or two blind cultivations can occur on schedule. See Chapter 10: Weed Management, for more information.
Insect Pest Management
Differences caused by variety selection, planting date, cultural techniques, site, and season cause great variations in soybean plant attractiveness to insect pests. If organic soybean farmers recognize these differences, they can manage the crop for reduced insect pest numbers or, when this is not possible, predict which fields are attractive and may need more attention to prevent yield loss. The organic soybean grower can normally rely on three factors to limit insect damage: reducing soybean attractiveness to pests, beneficial insects that reduce pest numbers, and the plant’s ability to compensate for insect damage (tolerance). Important tactics used to reduce insect damage include the following five strategies:
Rotation helps reduce levels of pests such as grape colaspis and often improves crop health. Avoiding pests through rotation of at least two years allows soybeans to tolerate the feeding of pests that later move into the field.
For pests associated with the seed or soil or for those that harbor in stubble or residue, tillage can be an effective management method. For example, Dectes sp. stem borer harbors in soybean crowns after harvest over the winter. Research has demonstrated that burying stubbles to a depth of 2 inches can decrease larval survival and adult emergence. Mortality is higher on poorly drained land or when conditions are relatively moist. Seedcorn maggots, which can consume germinating seeds, can be reduced using tillage
Soil fertility and pH maintenance
Thin plant stands often have more corn earworms, but good growth reduces attractiveness. Reducing plant stress from low pH, poor fertility, or inadequate moisture will enable plants to better tolerate insect feeding.
Variety selection and early planting
High caterpillar populations can often be avoided by early planting of an early-maturing variety (such as varieties from maturity group V and VI). These plantings will bloom and harden off before the corn earworm moth flight from corn fields, and the plants will be unattractive to the moths. Also, early maturity can greatly reduce soybean looper, velvetbean caterpillar, and late stink bug infestations. Double-cropped soybeans that are planted to Group VI or VII are common on organic farms. Percentage of loss from insects is generally 5 percent to 25 percent but can be as high as 50 percent. In rare situations, stink bugs can be trap-cropped by early-maturity fields, leading to greater damage. Early-planted fields are generally more susceptible to colonization by Dectes sp. stem borer and bean leaf beetle. However, planting soybean at the recommended rate and avoiding thin stands can reduce stalk girth and reduce the incidence of Dectes. Finally, beneficial insects often will colonize and establish in early-planted soybeans, helping to reduce the abundance of pests that arrive later in the season.
Variety selection can be important to manage certain insect pests. For example, lesser cornstalk borer can be a pest on drought-prone and sandy soil. Research has demonstrated differences in injury due to this pest that ranged from 9 to 31 percent among varieties. Data will soon be available at Field Crop Entomology.
A complete canopy allows a higher level of biological control by insect predators, parasites, and diseases. Also, narrow-row soybeans seem to be less attractive to egg-laying corn earworm moths.
Group V or later-maturing varieties that are planted after late May can become infested by corn earworm moths moving from corn. These moths produce pod-feeding corn earworm larvae, and a high infestation may reduce yield by as much as 50 percent. Also, populations of leaf-feeding caterpillars (green cloverworm, soybean looper, and velvetbean caterpillar) may occasionally damage soybeans. These worms are usually very late-season pests. In instances where caterpillar pests are not avoidable, insecticides approved for organic production, such as spinosads or Bacillus thuringiensis (Bt), may be successfully used. Scouting and the use of thresholds will indicate which fields are at risk. For scouting procedures for corn earworm see Field Crop Entomology.
Major Soybean Insect Pests and Disease Management
Corn earworm and tobacco budworm
Corn earworm and tobacco budworm are some of the most destructive insect pests of soybean, through pod feeding and sometimes foliar and flower feeding. Their biology is very similar. In conventionally managed soybeans, tobacco budworm is more tolerant of certain conventional insecticides than corn earworm. However, from the point of view of the organic soybean producer, the distinction is largely unimportant. These insects will often infest soybeans in late July or early August. Cultural management tactics are the most important. Soybeans will be less attractive to these pests if blooms are not present, if the canopy is closed, and if there is little young, newly grown, vegetation. Remedial management using a spinosyn or Bt can be highly effective.
The stink bug complex has been growing in importance as a pest group in soybeans. These insects injure soybeans by feeding on developing seeds inside pods. As already mentioned, early-maturing fields can occasionally attract high densities of these pests. In general, however, earlier-maturing and earlier-planted soybeans are less susceptible to stink bug infestation than later-maturing and later-planted soybeans.
The defoliating soybean looper is a year-round resident of more southern areas, but it migrates into North Carolina each year. Peak larval population densities occur in September and are most prevalent on late-planted or later-maturing soybeans. Soybean can tolerate a relatively high amount of foliar feeding, compared to other crops. Remedial management using a spinosyn or Bt can be highly effective.
Bean leaf beetle
Bean leaf beetles overwinter as adults and emerge over a three-month window during the spring in North Carolina. Adult beetles can injure soybeans by feeding on the foliage. The first full-season soybeans to sprout in an area will attract many of the strong-flying beetles. Soybean can tolerate a relatively high amount of foliar feeding compared to other crops. There are two generations of bean leaf beetle per year in North Carolina.
Soybeans have very few disease problems. This makes disease management in organic soybeans relatively easy. Nematodes are the main soybean disease agent in North Carolina. However, Asian soybean rust is a possible problem and, if present, will require much more intensive management to make organic soybean production viable.
The best way to avoid nematode damage is to plant varieties that are resistant to the nematode (and race) present in the field. These varieties can be found on the website NC Soybean Variety Information or obtained from county Extension agents. Conventional nematicides are prohibited in organic agriculture. Crop rotation of at least two years will probably help reduce soybean cyst nematode populations, but rotation is not as useful when dealing with root knot nematode because it has multiple host plants. If nematode damage is suspected, collect samples from the field (fall is the best time) and send them to the NCDA&CS laboratory for nematode essays: 1040 Mail Service Center, Raleigh, NC 27699-1040, 919-733-2655. The laboratory will identify a nematode population and species, if it is present. The Agronomic Division of NCDA&CS also has nematode management and assay information online at Nematode Assay Forms & Information.
Asian soybean rust
Asian soybean rust is a disease that has the potential for causing severe economic damage in North Carolina soybean crops. It must be considered when managing for soybean disease. To manage soybean rust potential in organic soybeans in North Carolina, select early-maturity groups or plant early to get the plants out of the fields in time to avoid the rust inoculum, or do both. Do not, however, create such an early-maturing soybean crop that yields are substantially reduced. If your crop is at risk of Asian soybean rust, there are a few sprays labeled for use in soybeans that can be found on OMRI.
For more information on soybean rust, visit one of these websites:
- Soybean Rust (USDA site on Asian soybean rust)
- Asian Soybean Rust: Notes and Organic Control Options for Farmers (Appropriate Technology Transfer for Rural Areas document on possible organic treatments for Asian soybean rust)
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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