Figure 1. Soybean cyst nematode female cysts on soybean roots.
Soybean Cyst Nematode (SCN) in S.D.
According to the U.S. Drought Monitor, most of the soybean growing area in South Dakota is currently under abnormally dry or moderate drought conditions as of the week of July 10. While these conditions negatively affect plant growth and progress, they unfortunately promote high population density of the soybean cyst nematode (SCN). Growers are encouraged to scout their soybeans for the presence of SCN on the soybean roots and well as submit a soil sample for SCN testing. For growers who already know the status of their fields, periodic SCN sampling is encouraged in order to determine whether the status has changed or if SCN numbers have changed.
Scouting for SCN should be done by uprooting soybean plants with a spade and gently removing the soil to expose the small fine roots without stripping SCN off the roots. SCN can be seen on soybean roots (Figure 1). They are the size of a period at the end of a sentence. They may be seen better with a magnifying glass. Because SCN can be highly variable in a field, examining roots is not the best way to determine the presence of SCN. The best method is to take a soil sample and submit to the SDSU diagnostic lab. This test is free of charge, courtesy of the South Dakota Soybean Research and Promotion Council.
When sampling for SCN, pay attention to the field entrance, along fence lines, low spots, previously flooded areas, waterfowl activity areas, high pH areas, and low yielding/stunted portions of the field. Collect 20 soil cores 0-8” deep from these areas in a zig-zag pattern using a soil probe or a spade. The soil cores should be thoroughly mixed and put in the soil sample bag or a zipper top plastic bag. Larger fields should be divided into smaller portions between 10-20 acres and each portion sampled separately. The soil samples should be kept at room temperature or in a cooler until shipped to the SDSU Plant Disease Diagnostic Clinic.
|South Dakota State University
153 Plant Diagnostic Clinic (SPSB), Box 2108
Brookings, SD 57007
SCN cannot be eliminated in a field once detected but it can be managed to keep the population low. The first approach to SCN management is to use resistant cultivars. Resistant cultivars play two roles: they are able to give high soybean yield in SCN-infested soils and they also prevent SCN numbers from increasing. The second approach is crop rotation to non SCN hosts like corn, alfalfa, small grains, sunflowers, flax, and canola. For highly infested soils (>10,000 eggs), longer rotations out of soybeans for several years may be necessary to bring the SCN numbers down. Rotate within SCN resistant cultivars. This ensures that SCN populations that can overcome a given resistance do not develop because of growing the same cultivar over and over. For fields with high SCN numbers, use of nematocide seed treatments such as Ilevo, Clariva, and Avicta Complete Beans, may help reduce SCN numbers and also increase yield. However in our field testing of nematocide seed treatments, we have not obtained consistent yield gain to pay for the treatment. This may be attributed to low SCN numbers at our test plots.