Planting wheat and grass cover crops may significantly reduce soybean cyst nematode (SCN) reproduction when planting soybeans into the stubble.
Controlling SCN is challenging today. Rotations with corn, planting resistant varieties and seed treatments aren’t a total cure-all. In combination they do help keep egg count at bay. But the genetic resistance we have been depending on (PI88188) is not nearly as dependable as it once was and there is nothing new on the horizon.
Planting corn for two or more years in combination with the above practices is probably the best practice we can implement at this time if we want to grow soybeans and minimize the impact of SCN on yield. Remember, most yield loss due to SCN is unseen without any plant symptoms.
But recently, I became aware that planting soybeans into wheat stubble or grass cover crop stubble may be able to significantly reduce SCN reproduction. This strategy, if it is effective, would be another tool in the toolbox to manage SCN and would join rotations, resistant varieties and seed treatments.
Mike Plummer, retired University of Illinois extension educator, has shared data from a trial that shows how both cereal rye and annual ryegrass cover crops reduced egg counts. This single chart has made it around the Corn Belt and attracted a lot of interest from SCN experts. If, in fact, this data is real and repeatable, this becomes another tool and a benefit gained from planting cover crops. And when it comes to planting covers, planting a grass before a broadleaf crop like soybeans is recommended.
But that is not the only data. In the early 1990s scientists from the University of Kentucky examined the effects of no-till and tillage of wheat residue on SCN cyst and egg populations after wheat was harvested and the field was planted back to soybeans in a double-crop rotation. Their research showed that SCN cyst populations after wheat harvest and before soybean planting were unaffected by the presence or abscence of wheat residue. However, by soybean harvest the presence of SCN cysts was reduced where wheat residue remained on the surface vs. tilled into the soil and decomposed.
Again, this is one study in Kentucky, but the results are promising. What we need is validation that winter wheat, either as a cash or cover crop, cereal rye or ryegrass residue can reduce SCN reproduction and significantly drop egg count when soybeans are immediately planted into the stubble.
The full citation for the Kentucky study is Hershman DE, Bachi PR. Effect of wheat residue and tillage on Heterodera glycines and yield of doublecrop soybean in Kentucky. Plant Disease 1995;79:631-633. If you would like a pdf copy of this report send me an email.
Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at email@example.com or ring him at 402-649-5919.