Of all the diseases that can impact soybeans, the most common still is soybean cyst nematode (SCN). This small roundworm is very common in Illinois and often slightly robs yield without growers noticing any symptoms. So it is good to check every so often to determine the size of the population in the soil, if it’s changing and if you need to take action.

Fall is the best time to sample for SCN. Samples can be collected from fields that will be planted to soybeans in 2016 or in fields where soybeans were just harvested, particularly if yields were low for no apparent reason. Results will also show if your SCN management strategies are working.

Collecting soil samples to check for SCN is not difficult. A few simple guidelines to follow are:
• Sample with a soil probe to collect soil cores.
• Collect soil cores to a depth of 6 to 8 inches—same as you use for soil testing.
• Collecting 15 to 20 soil cores from every 20 acres often is recommended.
• Combine cores in a bucket, mix and place subsample into a soil sample bag.
• Send to a private soil-testing laboratory or the University of Illinois Plant Clinic.

Suzanne Bissonnette with the Plant Clinic explained that they can do a number of protocols with SCN:
• ID presence of SCN in a soil sample
• Extract cysts from soil, process to retrieve viable eggs and count to determine population. This information then is used to determine if a sample is over the population threshold.
• Grow SCN populations in the greenhouse to inoculate differentials to determine Hg type. We conduct an SCN screen for growers to aide in variety selection and we conduct a full Hg screen for researchers/breeders. In each case the decision is based on egg count.
• Process roots to determine number of cysts attached for chemical trial researchers.
• Maintain a number of Hg populations for researchers.

It won’t be a surprise if SCN is found in Illinois fields where soybeans have been grown. SCN is widely distributed in the state and once established, the nematode can survive for years without a soybean crop being grown.

Managing SCN should involve using multiple tactics:
• Growing non host crops such as corn, wheat or alfalfa
• Rotating out of soybeans for several years if populations are excessively high
• Planting SCN-resistant varieties and using different sources of resistance
• Treating seed with a nematicide seed treatment

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or leave a comment below.