With this year's drought conditions, soybean cyst nematode intensified the stress on soybeans in many fields. University of Illinois Plant Diagnostic Clinic and IPM coordinator Suzanne Bissonnette says the high levels of the pest can cause the yellow patches that growers may have seen in fields.
Although the symptoms were easy to see this year, Bissonnette warns that in more typical years, low to moderate levels of SCN may be present in a field without visible symptoms on the above-ground part of the plant.
"To determine with certainty the SCN status of your soybean field, you must sample," she adds.
Fall is an ideal time to do this. With overwinter survival of SCN at close to 100%, fall sampling provides a good estimation of the population that will be present at planting and gives time to prepare for variety selection for next year's soybeans.
"All fields where soybean will be grown should be evaluated for SCN," Bissonnete says. "This nematode is a survivor."
"Once present in a soybean field, SCN is nearly impossible to eliminate," she continues. "It survives even in the absence of a good host. As it is very difficult to reduce high SCN levels to a manageable population, SCN management should focus instead on keeping the SCN egg count low."
One sample should represent no more than 10 acres and comprise 20 to 30 subsamples, each taken at a depth of 8 to 10 inches. Mix the subsamples together in a bucket, remove enough soil to fill a 1-quart plastic bag, and mail the bag to a qualified laboratory for analysis. Results will be reported in either number of cysts, or in the number of eggs, per 100 cc of soil.