Problem diagnosis: Soybean cyst nematode
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Now is an ideal time to begin scouting soybean fields for symptoms caused by the feeding of soybean cyst nematodes (SCN). Symptoms typically become obvious in July and will remain evident until the plants senesce after frost. The most obvious secondary (above ground) symptoms caused by SCN are stunting and chlorosis (yellowing). Yields can be significantly reduced. It is worth noting, that SCN can reduce yields up to 30 percent without the production of any above ground symptoms. This is typical with new infestations as the population densities of the nematodes increase to levels that result in obvious damage.
Unfortunately, many fields in Michigan are infested with SCN and growers are well aware of its presence. However, in many of our counties, SCN is infrequently detected, so growers may not be as diligent in their scouting. If SCN has not yet been detected on your farm, it is advised you collect root and soil samples and submit them to the MSU Diagnostic Lab for nematode analyses. The cost of these analyses (up to 20 samples per grower per year) will be paid for by the Michigan Soybean Promotion Committee as part of their “Beat the Pest, Take the Test” sampling program. I strongly urge all soybean producers to take advantage of this free program.
If SCN-infested plants are dug out of the soil and the roots observed, SCN females can be seen with the naked eye. They will be small white objects about the size of the head of a straight pin. Females will be more prevalent at certain times of the growing season but can be seen from about six to eight weeks after planting to harvest.
Even if you observe SCN females on plants, it is still recommended you send soil to the Diagnostic Lab. The majority of an SCN population is usually comprised of cysts (the dead remains of the females) present in the soil. Management recommendations are based on the numbers of eggs present within these cysts. Unless you have Superman’s vision, there is no way to stare at the soil and count the number of cysts present. To assess the numbers of SCN, it is necessary to collect soil and have the sample analyzed in a Nematology Lab.
Questions or concerns about soybean cyst or any other plant-parasitic nematodes can be addressed to me at 517-432-1333, Angela Tenney (517-353-8563) or Dr. George Bird (517-353-3890). SCN is the most important disease causing organism on soybeans. Don’t let SCN rob your yield, always remember to take the test, to beat the pest. If you haven’t done so in the past, to submit a sample for a free SCN analysis obtain a form from your county Extension office, the soybean office or our lab, fill it out and send it with the sample. The address for Diagnostic Services is provided on the form. Typically, results will be returned within two weeks of sample submission.