After harvest is an excellent time to soil sample for the soybean cyst nematode (SCN). Currently, 58 of Kansas’s 105 counties are known to be infested (Figure 1).
Figure 1. Current map of Kansas counties with known soybean cyst nematode infestations. Map created by Doug Jardine, K-State Research and Extension.
In fields currently infested, knowing your nematode population numbers is an excellent way to determine if your management plan is working. If numbers are going up, you know that the population of nematodes in your field have overcome the resistance in the most recently planted soybean variety and that use of that variety should be discontinued in infested fields.
Sampling the soil in a known infested field is very similar to collecting a soil fertility sample. You will need a soil probe, a bucket, and a little elbow grease (Figure 2). Walk a “Z” or “W” pattern across the field. If the field was in soybeans in 2019, collect the cores from directly in the row, since that is where the nematodes are most likely to be found. One difference from fertility sampling is that the probe should be inserted to a depth of 6 – 8 inches. Collect 18 - 24 cores in the bucket. Mix the soil thoroughly, and then remove about a pint for the actual sample. Soil can be placed into the same type of white sampling bag used for fertility samples or into a re-sealable, gallon-size plastic bag. Avoid freezing the soil or exposing it to excessive heat after collection.
Figure 2. Tools needed for nematode sampling. Photo by K-State Research and Extension.
For fields with no history of SCN, you should concentrate on areas of the field that might be hot spots (Figure 3). Other than targeting potential hot spots, the sampling procedure is the same as outlined above.
Figure 3. Hot spots in fields where soybean cyst nematodes are likely to be found. Photo courtesy of the Soybean Cyst Nematode Coalition.
Samples can be taken to any K-State Research and Extension county office for shipping. They can also be sent directly to the K-State Plant Disease Diagnostic Laboratory:
1712 Claflin Rd
4024 Throckmorton PSC
Manhattan, KS 66506
Keep in mind that if you are too busy to sample this fall, any time is a good time to sample for SCN. Unlike other nematodes that move up and down in the soil profile depending on the season, the cysts are always there and move only with tillage.
For more information, visit the SCN Coalition website at https://www.thescncoalition.com.
Doug Jardine, Extension Plant Pathologist