Spring will be here before we know it. But, even in the winter management decisions can be made to reduce losses caused by some important diseases. The most damaging pathogen of soybean is soybean cyst nematode (SCN) and now is the time to make decisions to control it. If you have confirmed soybean cyst nematode on your farm, it’s important to actively manage them to drive population densities to low numbers and keep them low to minimize the damage they can cause.
Management of SCN can be easy and may not require additional input costs. In fact, the first management recommendation is to rotate the infested field(s) with a nonhost crop, most Nebraska producers are doing this already by rotating soybean with corn. For the first 1-2 years of corn production, SCN population densities are expected to decline 50-75% each year. Growing continuous corn for additional years still helps reduce SCN, but the rate of reduction is expected to decline and will never reach zero SCN eggs. Other nonhost crops, such as small grains and alfalfa are also good options to help reduce SCN populations.
In addition to growing corn or other nonhost crops, it’s very important to carefully select soybean varieties that have SCN-resistance and rotate the sources of resistance that are used. Unfortunately, we have had limited choices for SCN resistance for decades. More than 95% of SCN-resistant varieties were derived from a single source of resistance — PI 88788. In Nebraska, approximately 50% of SCN populations are able to reproduce on PI 88788. In some states up to 100% of their SCN populations can reproduce on PI 88788. When selecting your varieties, try to identify ones with SCN resistance that comes from other sources, such as Peking, which is becoming increasingly popular in commercially available varieties. The good news is we now have another source of resistance, PI 89772 is available this year in 2 new varieties from Syngenta brands, Golden Harvest and NK. These varieties are in maturity group 2.3. If you can’t find a variety in your desired maturity groups with a different source of SCN resistance, it’s important to at least use soybean varieties with a high level of PI 88788 resistance. That information is available in ratings printed in seed company catalogs or contact your seed company representatives for more information.
In addition to selecting the best SCN-resistant variety for your farm and rotation, you also have several seed treatment nematicide products available. These products may provide some additional protection and can increase yield 1-5 bushels per acre, based on the results from Iowa State University. Seed treatments are not a substitute for the use of effective SCN-resistant varieties whose yield can vary by 10 or more bushels per acre in fields infested with SCN.
Remember weed management can be important as there are several common winter annual weeds that are hosts for SCN and can allow them to infect and reproduce to higher population densities even when there’s no crop in the field. Winter annuals henbit and purple deadnettle are strong hosts for SCN. Field pennycress, shepherd’s purse, small-flowered bittercress and common chickweed can also be hosts for SCN.
If you don’t know or haven’t tested a field(s) recently to check SCN numbers, you can collect a sample any time of the year, in any crop field, as long as you can get a soil probe into the ground. Submit a soil sample for SCN analysis at no charge thanks to support from the Nebraska Soybean Board. Send samples to the UNL Plant & Pest Diagnostic Clinic or contact your local Nebraska Extension Educator for more information.