By DOUG GRAVES
Ohio Correspondent

COLUMBUS, Ohio — Recent rainy and cooler-than-normal summer temperatures may have been beneficial for some crops, but these conditions have created a white mold outbreak in soybeans throughout parts of Ohio. And it’s the first major outbreak of the disease in the state in nearly a decade.

White mold, also known as Sclerotinia stem rot, is a common fungal disease that spreads by infecting old, decaying soybean stem tissue or blossoms prior to flowering and during flowering. The fungus invades the plant by producing a compound called oxalic acid, which kills plant tissue and allows the fungus to take hold.
According to Anny Dorrance, a plant pathologist at Ohio State University, “the disease is affecting soybean fields mainly throughout southern Ohio and northeast Ohio.”

These parts of the state have received the most consistent rainfall.
The good news is that it takes a lot of disease to affect yields, and this outbreak will have limited yield impacts.

“Studies out of Iowa State have shown that it takes about 10 percent infection, heavily scattered throughout a field before you begin seeing a yield reduction,” Dorrance said.

“Right now, the infection is just in pockets throughout fields.
If we start seeing infection in 50 out of 100 plants, then we may be looking at upwards of 20 to 25 percent yield loss.”

For producers facing yields with visible symptoms, little can be done to stop the infection. Specialists do not recommend applying fungicides.

“Fungicides are generally used as a protectant, and when you have thick, white mycelium already infecting the plant, fungicides won’t impact that

fungus at all,” Dorrance said.

According to Dorrance, the fungus is resistant to chemicals. She fears the fungus will build up tolerance to the fungicide.

She added that fungicide applications should only be made prior to infection if conditions are favorable for fungal build-up.

Her recommendation for dealing with the white mold is Topspin M.
“For standard bean producers, we don’t recommend fungicide applications unless that producer is growing a high-yield bean,” Dorrance said.

And Ohio farmers are not alone in this battle against white mold. The pesky mold has appeared in Indiana, Kentucky, Illinois, Iowa and Pennsylvania as well. White mold has been spotted in northern Indiana. D. H. Scott, of the Department of Botany and Plant Pathology at Purdue University says white mold is nothing new in his state.

“Before 1980, Sclerotinia white mold of soybeans was rare in Indiana, but during the 1980s the number of fields with this fungus disease slowly increases,” he said. “Then, in 1990 weather conditions were very favorable for its development. Again in 1992 disease conditions were favorable and the stem rot was observed in many fields in the northern half of the state. White mold can survive for several years in the soil, and no disease resistant soybeans are available.”

Dr. Chad Lee, University of Kentucky Grain Crops Specialist, was recently summoned to a field in Boone County in northern Kentucky. Lee says the mold is only prevalent in his state along the Ohio River.

“Thus far we have seen just a few fields along the Ohio River that have white mold,” Lee said. “It’s the first we’ve seen of it in the past 20 years. Normally it’s too warm to develop along the river, but we have had the coolest July in Kentucky in the past 100 years. All of the mold we’re seeing is along the Ohio River and no further south of the Ohio River.”

White mold has made its presence in Illinois, too. According to Chad Bradley, Assistant Professor of Crop Science at University of Illinois, “white mold on soybeans has historically been observed sporadically in central Illinois, more frequently in northern Illinois and rarely in southern Illinois.”

Recent weather conditions in this state (temperatures below 85-degrees and wet) are favorable for the development of white mold. According to Bradley, cooler-than-normal and wet conditions have occurred in central and northern Illinois the last couple of weeks.
Alternate management practices for controlling white mold include crop rotation, good weed management and plant resistant varieties.

“But the challenge seed companies face is that major white mold outbreaks are so infrequent that it’s challenging to develop soybean variety resistant to this disease,” Dorrance said.
White mold is also being spotted in fields in Michigan, Iowa and Pennsylvania.