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Corn+Soybean Digest

New Illinois Survey Uncovers More Disease Problems in Soybean Fields

The survey is conducted in late August and early September of each year to determine the levels of various diseases as the soybean crop heads toward harvest. Primary funding is provided by the Illinois Soybean Checkoff Board.

"This year we are running into large numbers of fields in the northern and central parts of the state with severe outbreaks of charcoal rot," said Glen Hartman, USDA plant pathologist at the U of I. "Jason Bond and his team from SIU are finding the same results in their part of survey, which covers the southern half of the state. Basically, anywhere in the state you stop and look for it, you will find it."

Charcoal rot is caused by a fungus that can be found in the soil of virtually every field in the state. Symptoms of the disease will normally show up only during periods of hot, dry weather.

"Every time we have any drought conditions at all, we can get charcoal rot," Hartman said. "What happened this year is that we had a long dry period with high temperatures in August. Although the early part of the year had normal weather, this dry spell was enough for the fungus to take hold and cause the problems we are seeing right now."

He notes that charcoal rot causes the soybean plants to turn brown and mature early but does not often kill them outright before podding takes place, especially when the disease occurs late in the growing season as it did this year.

"Under the current conditions, yield losses could run from very little up to 30 percent," Hartman said. "The problem will most often vary greatly within the different parts of a field. At the same time, I received a call from a grower who had a field where 95 percent of the plants were infected. In many cases, the grower does not even know what is causing the problem in his field."

Hartman points out that there are currently no practical options for managing this disease.

"We do not have any resistant varieties available to recommend to growers," he said. "Rotation probably will not work because charcoal rot can infect corn and other common crops. The only way to control this problem is to irrigate or not plant soybeans in a field for 10 or 15 years, which is really not practical at all."

Hartman advocates a two-pronged research approach for dealing with the problem in the long term.

"We need to look at both bio-tech and tradition approaches to finding genetic resistance," he said. "Our screening for resistance so far has looked at only a small portion of the 16,000 soybean accessions in the USDA Soybean Germplasm Collection housed at the U of I. We may also have to extend the search to the wild progenitor of the modern soybean and the perennial relatives of the soybean."

He notes that one problem has been a lack of consistent support for those research efforts because the disease is so weather related and only occurs in years when there are drought conditions.

"If we had a two- or three-year period of dry weather, charcoal rot would suddenly become the most important disease threat to our soybean crop," Hartman said. "To be proactive, we should maintain a vigorous screening program even during those years when it is not a problem. Eventually we could have resistant soybean varieties available for growers to plant as insurance against this potentially troublesome disease."

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