New White Mold Strain Could Become a Problem for Southern Farmers

If a new strand of white mold fungal spores enters the U.S. it could mean trouble for growers in southern states. ( Sonja Begemann )

A recent discovery in Brazil shows that white mold, while typically just a problem for northern states, could take root in southern states—if this strain makes it to the U.S. White mold is commonly listed as one of the top 10 diseases in the U.S. and leads to significant yield loss in affected states.

“White mold, also known as Sclerotinia stem rot, occurs worldwide, and the pathogen attacks and causes disease in many different crops. In the U.S., the fungus needs a cold period like winter before it can produce microscopic spores that infect soybean flowers in the summer. But in Brazil, the fungus does not need a cold period to produce spores,” says Glen Hartman, a USDA Agricultural Research Service research plant pathologist and professor in the Department of Crop Sciences at the University of Illinois.

The concern is what could happen if the strains are imported to the U.S. or if the country’s current strains adapt to warmer temperatures? Farmers in the south are unfamiliar with the disease which could leave them virtually defenseless.

Hartman worked with other researchers to evaluate what the U.S. versus Brazilian strains do without being exposed to cold temperatures, mimicking what the virus experiences in South America and could experience in the southern U.S. The group tested soybeans, common beans and canola plants to see if the fungus caused symptoms.

“All strains, regardless of their origin, were more likely to produce spores at a pleasant 68° F than at 86° F,” the study indicates. For states that routinely reach high temperatures this might be a good sign. However, Hartman notes there have been isolated southern outbreaks in St. Louis, Mo., and even Kentucky.

“That outbreak in Kentucky is kind of curious. I think that’s the furthest south we’ve ever seen it in the U.S. in a summer crop,” he says. “If that happened once, can it keep going? We don’t know, but it’s out there.”