Soybean cyst nematodes are a problem for some farmers every year, says Chris Tingle, soybean specialist with the University of Arkansas Cooperative Extension Service. He says crop rotation and variety selection remain among the best methods for controlling these pests.
Tingle says nematodes can decrease soybean yields by more than 50 percent in fields where populations are high. Last year, nematodes were severe in Prairie County, Ark.
“Symptoms arise from a plant being drought-stressed from a poor root system,” says Tingle. “In a rainy season, many soybeans have shallow root systems, and cyst nematodes will jump on and make the problem more acute.”
Severely infected plants are stunted. Cyst nematodes rarely kill soybeans, but hot and dry conditions increase the damage.
Developing a soybean species that's resistant to the disease-causing pest is a long, drawn-out process, according to Tingle.
“We don't have the tools yet,” Tingle says. “We don't have the right package in many soybean varieties to use in cyst nematode infested fields.”
How bad a field is affected by nematodes has a lot to do with crop rotation. Rotating crops between corn, grain sorghum and cotton helps reduce soybean cyst nematode populations.
How often the producer rotates out of soybeans really determines how effective crop rotation can be. “What we're essentially doing is eliminating a food source for the soybean cyst nematodes,” Tingle says.
However, if a producer has a severe problem, a single-year rotation and then back into soybeans may not be that effective. This is a complex problem that takes years to get the right production system worked out.
“In our verification fields where rotation practices were employed, nematode populations have declined annually. The decline isn't at a rapid rate, though.”
There are 16 different races of soybean cyst nematode, and any one could exist in a field. Soybean variety selection is the most important step in preventing yield loss. Before varieties can be recommended, an accurate estimate of a soybean cyst nematode race must be determined. County Extension offices will send soil samples to the Arkansas Nematode Diagnostic Laboratory.
Soybean varieties that contain some of the genetics from older “Hartwig” lines offer some options for producers. These have been shown to be effective in reducing soybean cyst populations and are now commercially available, but yield potential of this variety is limited.
Tingle has compiled nematode information for agents and producers. The data can be found at Extension offices and also in the soybean section at www.uaex.edu.
“The document explains symptoms, the proper way to sample, the proper way to check roots and other nematode details,” says Tingle. “It's in a reader-friendly format and there are plenty of pictures.”