Soybean cyst nematodes (SCN) are one of the most detrimental pathogens of soybeans—they are considered the No. 1 yield-robbing pest for United State soybean farmers. Nematodes in general account for billions of dollars in crop loss worldwide each year. According to the United Soybean Board, SCN affects farmers in more than 30 states and causes an estimated loss of $1.5 billion worth of soybean production annually. A lot of this loss goes unnoticed as SCN often shows no visible symptoms on the plant. If the plant is under stress it may show signs of yellowing, but the damage and yield losses have already occurred by that time.
Besides visually observing cysts on roots, soil sampling is the best method to determine SCN presence and population densities. The best time to sample for SCN should be when their populations are at their highest, which is typically right after harvest. Samples should be taken once every 4 – 6 years during the same timeframe to determine the status of the population. If sample results show heavy infestation you should consider more frequent sampling.
Research at Iowa State University shows conclusively that SCN are adapting and reproducing on the PI 88788 resistance source. PI 88788 resistance is currently used on over 95% of the resistant soybean varieties. If SCN are becoming more resistant to the current soybean varieties what other management activities, besides rotation, can farmers adopt to help suppress and reduce populations?
Can cover crops help reduce SCN populations and, ultimately, increase yields? The answer to this question is complicated, mainly because there has been limited research into how cover crops affect SCN and the research that has been done has seen highly variable results and been on a small scale. And SCN populations are highly variable across fields.
Some of the functions of cover crops are to improve soil health, increase above- and below-ground diversity, and increase organic matter. As the health, organic matter and diversity increase the function of the soil improves. This ultimately provides more balance in the soil, which can help reduce SCN populations. According to Dr. Nathan Kleczeski, Field Crop Plant Pathologist with the University of Illinois Department of Crop Sciences, cover crops diversify carbon and nitrogen sources and increase the soil micro- and macrofaunal diversity associated with reducing pathogenic nematodes, including SCN.
The Illinois Soybean Association is currently funding research looking at the potential of wheat in the double-crop soybean rotation to assist in the fight against SCN. The research is intended to build off previous double-crop trials in Kentucky that showed a potential reduction of SCN populations.
In the meantime, farmers should practice good crop rotations with non-host crops and consider improving the health of their soil by using cover crops.