Soybean and dry bean growers across the Midwest and North Central U.S. need to prioritize white mold when evaluating their "disease watch list" for 2012.

White mold, also known as Sclerotinia stem rot, was first discovered in the United States in the late 1800s on tomatoes. Since then, the pathogen has been found on hundreds of other crops and by 1992 it had established itself as a widespread problem in geographies where climate provided optimum conditions for disease proliferation.

When left untreated, white mold can cause yield loss or total crop loss depending on the infected crop, with the added challenge of lingering in the soil for up to 10 years.

The reason behind the rapid increase of white mold has yet to be determined, but it is thought to be related to changes in cultural practices that promote a greater canopy density. The increase in white mold is also believed to be influenced by changes in the genetic base of current soybean and dry bean varieties, or changes in the white mold pathogen. In the Northern U.S., it may be related to wet climate cycles that have persisted year after year.

“The optimal climatic conditions throughout North Central states can make white mold a serious threat for our growers,” says Dr. Sam Markell, Extension plant pathologist at North Dakota State University (NDSU) in Fargo. “Combine that with the lush, dense canopy that you find with many high-producing varieties of soybeans and you just have a great environment for the disease.”