Sampling Fields for Soybean Cyst Nematode (SCN)
Soybean cyst nematode (SCN) is a microscopic parasitic worm that attacks the roots of susceptible soybean and dry edible bean, causing unseen or unexplained yield losses. Soybean and dry edible bean are naturally susceptible to SCN, but through plant breeding, most soybeans have some level of resistance, varying in level from good to poor. The most common source of resistance to SCN in soybean is PI88788, which is about 30 years old, and many soybean growing areas have SCN populations that are becoming resistant to this source. The Peking source is a very effective SCN resistance source but is only available in less than 5% of all soybean varieties.
Soybean cyst nematode cysts each harbor hundreds of eggs. Cysts and eggs of SCN can survive in the soil and remain viable for many years even without a soybean or dry bean host. Any activity that moves soil around will move SCN, meaning that areas with a history of soybean production likely have or will have this pest. Soybean cyst nematodes were first reported in Minnesota in 1978, South Dakota in 1995, North Dakota in 2003, and Manitoba in 2019.
During the growing season, the developing SCN cysts containing the eggs can be seen on susceptible plant roots, as seen in the picture below. To get an accurate assessment of the infestation level of the field, you need to collect soil samples and submit them to a laboratory to get a measure of the SCN egg count.
Photograph of soybean roots with SCN cysts. Photo courtesy of NDSU.
SCN sampling strategies
The best time to collect SCN soil samples is at the end of the soybean growing season, right before harvest or just after harvest (before fall tillage starts). Fall soil sampling for SCN coincides with the highest egg counts in soil and typically falls in the months of September and October.
Collect 10-20 soil cores (6 to 8 inches deep) in the soybean row where SCN is likely present. Your goal is to collect infected soybean root tissue and capture the SCN cysts and eggs in the soil sample. Since SCN is a soil-borne pest, it moves wherever SCN-infested soil can enter the field. This includes field entry points where infested soil can be transferred on equipment and tires, places where wind-blown soil accumulates (e.g., fence lines), drainage ditches and flooded areas, and locations with consistently low soybean yield. Mix the soil cores together and take a subsample to fill the soil sample bag.
If you have never tested for SCN before, you will want to sample fields intended for soybean or dry bean for the presence of SCN and gather a baseline SCN egg count. If you know you have SCN, you will want to sample soybean fields twice during the year: once in June to get an initial SCN egg count and then again in the fall to get a final SCN egg count. The early and late SCN samples allow you to measure if SCN populations are being effectively controlled (i.e., no increase in SCN egg count) or if the soybean variety SCN resistance source is failing (i.e., SCN egg count increases). Choose a single point in the soybean field and collect 8-10 soil cores (6 to 8 inch soil depth) taken within the soybean row at that spot. Mix the cores together and fill a regular paper soil sample bag. Mark that point with a flag and collect its GPS coordinates. Come back to that exact spot in the fall and collect a second sample. This will help you assess how your SCN management strategies, including the soybean variety SCN resistance source and soybean seed treatment, are working in the field.
Preparing and sending SCN samples to AGVISE Laboratories
Please submit SCN soil samples on the bright-yellow SCN submission forms or use the online SCN submission option in AGVISOR. AGVISE provides special SCN submission forms and online label sheets at no charge. The bright-yellow forms and stickers helps us identify these special SCN samples and ensure that the SCN samples are not accidentally dried and ground like regular soil fertility samples.
All SCN samples are analyzed at the Benson, MN laboratory. You can send the SCN samples directly to the Benson laboratory (see address below) or to the Northwood laboratory, where we will forward them to Benson for analysis. AGVISE Laboratories reports SCN results in “eggs/100 cc” of soil and provides interpretation on the SCN report informed by university research.
Helpful resources
Soybean Cyst Nematode Resource Compendium, Iowa State University
Soybean Cyst Nematode (SCN) Management, Univ. Minnesota
Soybean Cyst Nematode in South Dakota: History, Biology, and Management, SDSU