INVESTING CHECKOFF DOLLARS
WATCH FOR SOYBEAN CYST NEMATODE FOLLOWING DROUGHT.
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ast season’s drought might have lingering effects in the form of soybean cyst nematode (SCN) populations, according to Connie Strunk, plant pathology field specialist for South Dakota State University. “We tend to see more SCN populations and explosions after a drought, so we’re expecting to see quite a bit of SCN within the upcoming growing season,” said Strunk. “Reproduction happens much more quickly in drought conditions which leads to more generations and ultimately higher egg counts.” In addition to surviving for long periods in fields where soybeans or other host plants have grown, there are other reasons why SCN proliferates following dry years. “Most likely, because those cysts remained in the soil, it wasn’t able to move around with, let’s say, water or wind,” said Strunk. “They just remain within that soil ten years or more.” Each tiny cyst can produce over 300 eggs, explained Strunk, “and so when they do emerge from that cyst or hatch, they look for the soybean roots.” There are some weeds that can also be a host for SCN, adds Strunk. “They utilize those roots for reproduction or to sustain their population.” Even though there is little hope of SCN eradication once it’s in a field, there are ways to manage populations, according to Strunk. “We encourage considering variety selection, looking at the different [SCN] resistance to help break down those numbers, doing some crop rotation and even perhaps using a nematicide treatment to reduce that number, but it is a perpetual problem in South Dakota where we see SCN every year.” South Dakota’s first soybean cyst nematode was discovered in Union County, the state’s southeastern-most county, in 1995. With few exceptions, it’s now in virtually every soybeangrowing county in the state. Strunk says she suspects counties in which SCN has not been reported have simply eluded detection. “Soybeans could look great, green and growing,” she said, “but you still may have a 30 percent yield loss occurring because of SCN on its own.” The presence of SCN can be determined by soil testing long before there’s any visual evidence above ground. Soil testing at the SDSU Plant Diagnostic Clinic for the presence of SCN in South Dakota growers’ fields is paid for by the South Dakota Soybean Checkoff. “Whether it’s targeted sampling in that field or just an overall sample of areas that were low-yielding or lower-lying, we encourage some of those samples to get sent in,” said Strunk. “If they’d sampled in the past, they should continue to sample, just to see if what they’re doing is working to reduce those [SCN] numbers or keeping them in check.”
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Soybean cyst nematodes on soybean roots. Photo by Craig Grau, University of Wisconsin
Once the first cyst is discovered, it’s important to begin management quickly, said Strunk. “It’s much easier to reduce those numbers when they’re lower than when they get pretty high and out of hand,” she said, adding reproduction perspective to the 300 SCN eggs coming from a single hatch. “One cyst can give rise to over 27 million eggs.” Free soil tests are offered through SDSU Extension and can determine if SCN is present or if population numbers have changed. If SCN is found, Extension specialists can help producers with management options to reduce soybean damage. For producers who have not tested for SCN yet, soil sampling can be done anytime in spring, summer or fall. If previous soil tests have shown the presence of SCN, soil sampling for another test to detect changes in SCN numbers should be done in the fall after soybean harvest, as that is when the SCN population is at the highest in the soil. Check every two or three years to see if the SCN numbers are changing. If the numbers increase, that means whatever the producer is doing to control SCN isn’t working and changes need to be made. He says it’s easier to keep SCN populations down before they reach high levels in the soil. Soil tests are conducted at the SDSU Plant Disease Diagnostic Clinic. Farmers can mail soil samples to the clinic and are notified of the results within four to six days, depending on the volume of samples at the clinic. For information about soil testing, visit the Extension website: extension.sdstate. edu/hg-type-testing-management-strategy-soybean-cystnematode-control Download information on how to collect and mail soil samples at: bit.ly/SCN-Soil-Sampling-Info-Sheet
Summer Issue 2022
SDSL
