Disease Management: Tools to Manage SCN

It’s time to consider seed treatments as a tool to control Soybean Cyst Nematode (SCN).

SCN is still the No. 1 pest impacting soybeans in the U.S. We all know the management rules: plant a resistant variety, rotate out of soybeans, control winter annuals (alternate host), scout for presence of cysts and eggs, and, if egg counts in the soil get too high, rotate out of soybeans for 2 or 3 years.

SCN is still out there and still a drag on yield, but its importance as a risk to yield seems to have receded from memory because growers are doing practically everything they can already by rotating with corn and buying a soybean variety that already carries some PI88788 resistance. But these genetic sources of resistance seem to be breaking down and aren’t doing as good a job at controlling SCN. We all know overdependence on glyphosate led to weed resistance. Overdependence on PI88788 has led to increasing SCN resistance.

However, the pressure is still out there and probably still impacting yield without some of the visible plant symptoms that come with a heavy SCN infestation. Today there are additional therapies to add to your management plan to keep SCN populations at bay. Growers need to consider them, particularly if they don’t know what egg population exists in their soil.

You probably have had SCN present in your fields for a long time without realizing it was stealing 20 to 30 percent of your yield—sometimes as much as 50 percent. The vast majority of the time, SCN losses go unnoticed.

Syngenta is marketing Clariva® Complete Beans seed treatment that includes a new mode of action to control SCN. Its active ingredient is a natural parasite, Pasteuria nishizawae. It attaches to the SCN and multiplies inside it, causing it to die and rupture. When the SCN ruptures, it releases more of the parasite into the soil, where it continues its life cycle, suppressing the next generation of SCN. This is good example of biocontrol.

Bayer CropScience markets VOTiVO® to control SCN. VOTiVO contains Bacillus firmus. This bacterium creates a natural barrier to infection since it grows on root surfaces that come in contact with SCN and prevents the nematode from entering the root. They recommend treating seed with a 3-way fungicide: Poncho® (insecticide) plus VOTiVO and ILeVO® for control of SCN and sudden death syndrome (SDS). The presence of soybean cyst nematode is associated with SDS outbreaks.

If you are like most growers you are probably rotating and planting resistant varieties, yet don’t know how much SCN is impacting your yields since there are no visual symptoms. This is where a seed treatment comes in. It is complementary to your other practices and provides additional insurance that SCN is not robbing bushels at the end of the season.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.