SDS northward movement expands threat to soybean yields

Yield loss caused by sudden death syndrome (SDS) continues to plague growers throughout the Midwest. Researchers at Pioneer Hi-Bred, a DuPont business, say SDS-tolerant varieties are key to managing the disease.

SDS originally was considered an issue for the southern soybean-growing region, but now has moved as far north as Minnesota and as far east as Ohio. For many affected areas, SDS ranks second in economic losses only to soybean cyst nematode (SCN).

"There’s a 40 percent chance for growers in highly infested areas, such as those in Iowa and Missouri, to have 12 percent yield loss annually,” says Scott Nelson, a Pioneer agronomy research manager.

Conditions favoring disease development may result from early planting, high rainfall and/or low-lying, poorly drained or compacted field areas. Cool, moist conditions early in the growing season often result in higher disease incidence.

"Although infection occurs early in the season, symptoms usually do not appear until mid-summer,” Nelson says. The appearance of symptoms often is associated with cooler temperatures and high rainfall during flowering or pod-fill.

Soybean varieties with SDS tolerance often don’t incur the severity of symptoms non-tolerant varieties do. For this reason, variety selection is a key management practice to reduce plant damage and yield loss. To assist growers in choosing resistant varieties, Pioneer researchers rate products in multiple test sites with known historical SDS occurrence. Tolerance data are collected and analyzed across years to determine the appropriate SDS tolerance score.

Pioneer research efforts, including use of marker-assisted selection and the AYT™ system, are providing higher levels of tolerance to sudden death syndrome in high-yielding, elite soybean varieties. Pioneer now has varieties that score as high as an 8 for SDS tolerance on a 1 to 9 scale (9 being most tolerant).

"Growers saw strong yield advantages from elite Pioneer® brand soybean varieties,” Nelson says. “Compared to competitors, Pioneer soybean varieties lead the industry in SDS tolerance.

"Providing multiple resistance traits in the same variety is especially important to manage SDS, because both SDS tolerance and SCN resistance are frequently needed in the same product,” Nelson says.

Despite genetic tolerance, farmers may still encounter yield loss from SDS. Nelson says practices to minimize yield loss include improving drainage and avoiding planting windows when the seed will be in cold wet conditions. Managing soybean cyst populations through crop rotation and sources of resistance also will improve tolerance to SDS. "SCN problems can make the crop more vulnerable to SDS,” Nelson says.

SDS is a disease that easily can be confused with other diseases such as brown stem rot. For an accurate diagnosis, growers should consult their local agronomist.