For a limited time, we will have free soybean cyst nematode testing in the Kansas State University Research and Extension Wildcat and Southwind District offices and likely every other K-State Research and Extension office. Researchers are preforming a mass study of SCN in the area and they need all the samples they can get. Normally the SCN nematode test can be $15 to $20 but right now the only cost will be shipping off the samples. Please take advantage of this opportunity and you’ll be helping with important research and get a free SCN test for your soybean field.
This time of year right after soybean harvest is the best time to test for SCN. A regular soil probe is all that is needed to take a SCN test. Much like a soil fertility test, soil cores are taken in a six to eight-inch depth. The differences are all the cores need to be taken within the soybean planting row, at the bare minimum 15 cores need to be taken per sample, and the cores are taken from just the 1- to 10-acre problem area (rather than a sample for the whole field). The SCNs and their eggs can be highly variable so it is very important to be precise with the soil depth and take plenty of soil cores. Also, in this case, it is important to be consistent for the K-State SCN research project. We have soil probes available at each K-State Research and Extension office and if there are any questions on sampling procedures, please give us a call. A shovel soil sample won’t work in this case because precision and consistency is needed.
Any soybean field could be infected with SCN and often the damage they cause is hard to see, yet losses can be as high as 40% in some fields. In fact, unexplained yield loss in the main symptom and soybeans with SCN damage often end up having some sort of secondary problem like potassium or iron deficiency, seedling blight, charcoal or Phytophthora rot, or less drought resistance. Yield loss can occur without any symptoms at all but the first noticeable symptoms will be in roughly circular spots or along field edges. The soybeans will have fewer roots and root nodules. In extreme cases the SCNs can kill the plant outright, but often it’s the soil diseases they allow into the plants that kill. If there is an area in a field that always has issues with soybeans it could be because of SCN, and now is great time to test for them.
So a field is plagued with SCN, now what? There are some soybean varieties that are more resistance to SCN and continued use of those varieties can reduce populations over time. However, this can’t be only control strategy because over time the SCNs in the field will also become better at attacking those resistant varieties. Delayed planting dates, like those in wheat-double crop soybean rotations, tend to have lower SCN because of the timing of plant growth. Also, group V soybeans grown in southeast Kansas tend to have less yield loss, likely also do to physiological timing. SCNs tend to be worse in tilled fields rather than no-till, and tillage is another way for them to spread out their infected area. SCNs are not strictly soybean dependent and can also feed on some weed species like henbit, so weed control is important. Nematicides are available but their effect is short-lived. However, research has been done showing that a mustard cover crop, tilled in before planting, releases compounds that are toxic to SCN. The biggest control for SCN though will always be crop rotation. Corn, wheat, and sorghum are non-hosts, and combined with resistance soybean varieties, is the most important method of reducing SCN populations.
If you are interested in taking a SCN test, please give your local extension office a call. There are some details like field location and field history that needs to be collected for the research project.