By Anne Dorrance, Laura Lindsey, Terry Niblack, and Chris Taylor, Ohio Agricultural Research and Development Center, The Ohio State University
Did you know that over 60% of the soybean fields in Ohio are infested with soybean cyst nematode (SCN)? Thanks to Ohio Soybean Council support, researchers at The Ohio State University are focusing their efforts on understanding how SCN affects soybean production in Ohio so that best management practices recommendations can translate into more productivity for soybean farmers.
Dr. Laura Lindsey, soybean agronomist in the Department of Horticulture and Crop Science, working with nematologists Drs. Chris Taylor and Terry Niblack in the Department of Plant Pathology are documenting the distribution of SCN and its adaptation to SCN-resistant varieties. Nearly 500 soil samples have been collected from soybean fields throughout the state by Dr. Lindsey’s Lab and Ohio State University Extension educators, and the nematologists have determined that at least 61.3% of them have high enough SCN populations to be detectable. Out of those, at least 12% have what is considered high SCN egg counts, and these are candidates for HG Type testing to explain why the numbers are so high even though the farmers are presumably growing SCN-resistant varieties.
Almost all of the soybean varieties sold to farmers in Ohio are labeled “Resistant to SCN”, “Resistant to SCN Race 3” or something similar. Most of the time, a variety labeled as SCN-resistant got its resistance from an ancestral soybean line called PI (Plant Introduction) 88788. This source of resistance was considered broad-spectrum, highly durable, and relatively easy to transfer into the new high-yielding varieties via traditional breeding practices, and that’s why most of our soybean varieties have this resistance. Based on data from hundreds of trials in locations throughout the Midwest, varieties that have this source of resistance will yield higher than similar varieties with no resistance even when SCN populations are low. But, based on hundreds of trials in greenhouse studies, up to 1/3 of varieties labeled as resistant actually have no effective resistance to SCN. What does this mean for you, if you’re one of the soybean farmers in Ohio who have SCN? It means it’s “buyer beware!” You have to trust your seed source, but also trust your yield monitor and make sure you know whether your SCN egg counts are going up or down. If your SCN counts are going up year after year, you should consider switching to a different source of seed with different SCN genetic resistance. For information on sampling for SCN and interpreting egg counts, see http://ohioline.osu.edu/ac-fact/pdf/0039.pdf.
Management of soybean and optimization of profit in fields infested with SCN is best achieved by rotation with non-host crops and SCN-resistant varieties. With a non-host crop, such as corn or wheat, the SCN populations will decline by at least 35% in the first year. When a SCN-resistant variety is planted, egg counts should decline in a range from 0 to 50%. If you suspect you have a problem field egg counts need to be monitored over several years to determine if SCN reduction strategy is working. If you are monitoring the SCN in your fields and the egg counts are decreasing or staying low, then whatever you’re doing is working. If SCN populations are increasing despite your efforts switching to a longer rotation time and use a different source of SCN resistance in your soybean. The OSU soybean team is continuing to HG-Type testing of SCN populations from across Ohio and will be glad to include any problem SCN population you might have in their ongoing effort to better understand the challenges we have in growing soybean in Ohio.