Soybean yield loss caused by Sclerotinia stem rot (also known as white mold) was more widespread than usual last season.  While the fungus that causes the disease (Sclerotinia sclerotiorum) has traditionally been reported in pockets north of Interstate 80 in Illinois, plant pathologists report the disease was recorded throughout much of central Illinois in 2009.

The good news, says Glen Hartman, U.S. Department of Agriculture (USDA) plant pathologist at the University of Illinois, is that specific weather conditions that drive the disease may not be the same this year as in 2009.  Cool, wet weather between June 15 and July 15 is generally what spells trouble, he explains, and 2009 was exceptionally cool and wet throughout the state.

“Sclerotinia is hard to predict, but the chance of repeating the 2009 conditions during flowering would be unusual.  Some parts of the state would suffer some damage if those conditions occur,” Hartman says. “The 2009 season was a bad one for some farmers, and we do know the fungus can stick around in the soil for several years, waiting for the right conditions to strike again.”

Areas of heaviest crop density are the places where disease incidence may be higher.  Hartman notes that white mold typically appears in clustered areas of a field, not uniformly across an entire field.  These “pockets of high disease severity” are areas that may be in the bottoms of a hilly field or other places that hold moisture.  He suggests checking for the disease first in those places in the field where fog burns off last in the morning.

“Look for wetter pockets if you suspect you have Sclerotinia stem rot.  It may be possible to just treat those areas with a fungicide, rather than the whole field,” he says.  “Treatments can be hit or miss.  Timing of the spray is important and coverage is important.  The product needs to get down into the canopy, but that can be tough to do well in narrow rows and in wet fields.”

While no soybean varieties have resistance to the disease, Hartman encourages farmers to review ratings for white mold in the Varietal Information Program for Soybeans (VIPs).  He also suggests avoiding varieties found to be highly susceptible the previous year, if possible.

Hartman is actively involved with basic research projects to find plant introductions (PIs) that have resistance to the disease and provide that information to soybean breeders for consideration in their breeding programs.  So far, Hartman says the research is still at a level of discovery.

“Looking for high levels of resistance is not an easy task, and even the best material we have found so far isn’t that great.  We are evaluating not only soybean material for resistance but also other plant sources,” he says.  “The work will take time.”

Other research to solve challenges the disease poses are underway across the nation.  USDA’s Agricultural Research Service heads up the National Sclerotinia Initiative, which supports 20 different projects aimed at neutralizing the disease’s economic threat to soybeans and six other commercial crops.  Hartman is one of many scientists part of the consortium that includes 10 land-grant universities and five crop commodity groups like the American Soybean Association and the United Soybean Board.  For more information, visit www.whitemoldresearch.com.

-Funded through the Soybean Checkoff