CLAREMONT, SD (AP)--As South Dakota soybean acres have increased, so has white mold, a fungus that can hurt the popular crop.

"The disease affects the plant at flowering time in July and shows up on the stems first. By the time it's visible, the situation is pretty much hopeless. There's no effective treatment," said Gary Erickson, a Brown County Extension agent.

It's a highly contagious fungus activated by damp, humid weather. White mold aborts soybean flowers and cuts yields, said Erickson. It appears as stem lesions and makes the plant look dehydrated. There's no good way to rid it from the soil, he said.

"White mold can lie dormant in the ground for up to 10 years," Erickson said. "It builds up in the soil, so the more beans you plant, the more buildup you get. The disease thrives in damp weather like we've been having lately."

The disease became more prevalent as the early 90s brought more rainfall and humidity.

"Last year was one of the worst years ever," said Mike McCranie, a Claremont-area soybean farmer. "We lost about eight to 15 bushels per acre to white mold."

Farmers can apply a chemical during a two-week period in early July. But many deal with white mold by selecting different varieties, widening rows and cutting the number of plants.

"We had been using a variety that was prone to white mold, so we eliminated it," McCranie said. "We're trying to go with less bushy plants because they're less susceptible."

Bath-area farmers Jon and Loren Locken use similar tactics. They also are interested in finding new treatments and are taking part in a South Dakota State University study.

"We provide land and seed six test plots for the researchers," Jon Locken said. "They've been testing a variety of treatments, such as sodium bicarbonate and a herbicide called Topsin."

The white mold study, started by SDSU plant pathologist Marty Draper, is in its third year.

"We started the study because we've seen the disease become more of an issue in South Dakota," he said. "We're looking at the viability of about 10 chemical and fertility treatments for white mold."

The study has not proved the effectiveness of any of the chemical treatments. It has shown it's important not to recommend these treatments, Draper said.

"We worked with a herbicide called Cobra that was thought to stimulate natural plant defense mechanisms in response to stressors such as white mold. However, we haven't seen real results with it and are finding that chemical controls don't offer a good return," Draper said.

"If you have an infected field, you need to be looking at crop rotation, row spacing and variety."

This year, the study will focus on fertility treatments and seed varieties, he said.

Soybeans in the Groton, Claremont, Hecla and Langford areas were hit hard by white mold last year. This year, it's too early to tell.

"We've had a lot of moisture and any more rain won't be good," Erickson said. "We need heat for the beans now because we're behind in the growing season."

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