Soybean cyst

By Jeff Burbrink
Extension Educator, Purdue Extension Elkhart County

Jeff Burbrink
Extension Educator, Purdue University Elkhart County

ELKHART — Reports of high populations of soybean cyst nematodes from tested fields are floating in from around the Midwest. SCN has been in our county for many years and seems to do especially well on our irrigated sands.

I have talked to a grower who is considering planting soybeans in fields that were in beans in 2021. Part of the reasoning is the higher price of beans relative to corn, and the higher costs and/or limited availability of some of the inputs for growing corn in 2022. This may not be a good idea if the SCN numbers in your fields are high.

SCN overwinters as an egg in the soil. They overwinter very easily in northern Indiana, whether our winter is harsh or mild.  If you must plant beans back to back, do consider using SCN resistant varieties that do not rely on PI 88788. This is by far the most common type of resistance built into today’s soybean seed, and it has lost much of its effectiveness, especially in fields with more than 5,000 eggs per 100 cm². In short, the nematodes have become resistant to the resistance.

Testing should be done every few years where beans are grown to assess the situation in your fields. You can visit www.thescncoalition.com to learn more about suggestions on testing for SCN.  In a nutshell, the equipment you need for sampling soil for SCN is the same equipment you use for taking a soil sample for soil nutrient analysis: a soil probe, a bucket, and a plastic soil bag.

To collect soil samples for SCN diagnosis, we recommend you collect 10 to 20 cores of soil, each with a 1-inch diameter and 6 to 8 inches depth in a 20-acre area. If the field is larger, break the field into 20-acre units and take 10 to 20 cores per unit.

Take cores from within root zones and use a zig-zag or M-pattern to collect soil cores. In addition, you may also want to include samples from a high-risk area, such as near a field entrance, areas where the yield seems to be a little lower than the last time soybeans were grown, or along fence lines where wind-blown soil accumulates.

Bulk the cores in the bucket and mix thoroughly. Take the time to mix the sample. The better the sample is mixed, the better it represents the whole field. Put 1 pint of the thoroughly-mixed soil in a plastic bag and label it with a permanent marker. Do not put a paper label inside the bag. For accuracy’s sake, keep the sample at room temperature or cooler and keep it out of the sun or hot truck cab until you are ready to pack and ship it.

You should also brush up on the changing language being used to describe SCN types.  We used to use the term “races” to categorize SCN, with more than 20 separate races identified.  They are now using the term “HG type” because the HG tests can measure how well the SCN populations can reproduce on various breeding lines used in resistant soybeans, which is much more useful.  Visit https://bit.ly/3FUgNNp to learn more about HG types and how they can be used on your farm.