Soybean Cyst Nematode Testing and Resistance

By Dusty Sonnenberg, CCA, Ohio Field Leader, a project of the Ohio Soybean Council and soybean check-off.

Soybean Cyst Nematode (SCN) is hidden pest for soybean growers in Ohio and across the mid-west. Each year the yield impact costs soybean growers millions of dollars in lost revenue.  When SCN is present in a field, even at very low numbers, it can multiply quickly if not managed properly. “It is much easier to keep SNC numbers low than it is to bring high numbers down,” said Horacio Lopez Nicora, Assistant Professor in Plant Pathology at The Ohio State University. “SCN females can produce up to 200 eggs, and there can be a new generation every 25-40 days depending on the weather.” The multiple generations of SCN and reproduction rate allow the populations to increase rapidly.

University research plots and commercial soybean field monitoring have shown SCN management to be critical in both high and low SCN populations. “We have conducted research looking into the how many SCN eggs can produced in a season to generate a reproduction factor for a field. These were commercial soybean fields,” said Lopez-Nicora. “We would pull soil samples in the spring before planting, and again in the fall after harvest. Some of those fields started with low numbers, ranging from 50 up to 400 eggs per 100 cc of soil in the spring. These are considered low numbers. What we found was that a field that started with low numbers but did not have a resistant variety of soybean planted, or a combination of resistance packages could increase dramatically. In some cases, by the fall those numbers had increased 15-20 times. Fields that started with higher numbers did not increase at the same rate due to the higher number of SCN already present and the amount of competition among them. There is an inverse relation between the reproduction factor and the initial population. This is common in nematology.”

SCN management begins with knowing the number of each field. “Low numbers of SCN are easy to keep down with a good management strategy,” said Lopez. “My recommendation is to always know your field SCN numbers, and if you have SCN and do not underestimate the situation. It is good to regularly check the numbers to be sure you are keeping them down. Otherwise, it is much more difficult to bring high numbers down.”

The Ohio Soybean Check-off has funded this SCN research since 2018, in conjunction with the SCN Coalition of the United Soybean Board. Farmers can submit two free samples to the nematology laboratory at The Ohio State University to be processed and analyzed for SCN numbers. Soil samples can be collected in the same manner as soil sampling for soil test nutrient analysis. The grower will receive the results telling them if they have SCN present, and what the number is for each sample. The goal is that farmers can take the proper management steps based on the SCN number.

There are 3-R’s of SCN management. “This is something Dr. Terry Niblack promoted in her review of SCN management,” said Lopez-Nicora. “The 3-R’s are: rotate, rotate, and rotate. The first rotate is to rotate to a non-host crop. Corn is a good example of a crop that does not serve as a host to SCN. The second rotate is to rotate between soybean varieties. Even though the same resistance source, such as PI88788, is the most common source used today, there are many varieties of soybeans that have that resistance source, but different genetic background in each variety. Those different genetic backgrounds help to mix things up. The final rotate is to rotate resistance sources. Some sources are highly resistant, and other sources of resistance, such as Peking, have other levels of resistance. By rotating the source of resistance, we are not allowing the same inoculum to build up in a field after multiple years of use. We are attempting to stay one step ahead of the pest.”