By Rich Maples

Lots of rainfall. High humidity. Temperatures in the mid-80s. Perfect conditions for diseases in soybeans. And perfect conditions for Cliff Coker, who rates the severity of diseases on soybean varieties.

"We want to rate the soybean varieties in a worst case scenario," said Coker, a plant pathologist for the Cooperative Extension Service, University of Arkansas. "We're here to protect the grower."

Coker rates disease severity on a scale of 0 to 9, with 0 meaning no disease is present. He checks every variety in the UofA's standardized soybean variety tests at the Cotton Branch Station at Marianna, the Rice Research and Extension Center at Stuttgart, the Southeast Branch Station at Rohwer, and the Northeast Research and Extension Center at Keiser.

Coker's work, which focuses on foliar diseases, frogeye leaf spot in particular, is funded by the Arkansas Soybean Promotion Board.

He notes that 1996 was a light-to-moderate year for frogeye leaf spot, at least at the soybean variety test sites. "There were isolated spots in the state where the disease was heavy."

Two other UA plant pathologists monitor soybean diseases in their field studies. Dr. John Rupe looks at sudden death syndrome (SDS) at the Marianna station, while Dr. Terry Kirkpatrick rates the severity of stem canker at the Southwest Research and Extension Center near Hope.

"Stem canker, SDS and frogeye leaf spot have been the three predominant soybean diseases in past years," Coker said. "We've had isolated cases of severe aerial blight. It's the same organism that causes sheath blight in rice, so we're going to see more problems in bean-rice rotations in fields with a history of the organism."

Coker said he monitors frogeye and other diseases on all 200 varieties in the standardized variety trials at Marianna, Rohwer, Keiser and Stuttgart.

"I look at three replications at each site to eliminate factors such as differences in soil type."

He added that in addition to his disease rating work, the Soybean Promotion Board is funding a study of 27 seed treatments with several products at different rates on three soybean varieties.

"We also have foliar fungicide evaluations--10 treatments replicated five times," said Coker. "We're not only evaluating products that are labeled now for soybean disease control, we're looking at products that we're attempting to get labeled for soybeans."

What can soybean growers hope for to control diseases in the future?

"I feel the new fungicides that are coming on-line are much more effective than anything we've had in the past," said Coker. "I think seed treatment will play more of a role.

"In the past, we've gotten 60-70 percent control of a disease with fungicides. With some of the new products, we are looking at 90 percent control or better."

For now, one of the best things a soybean grower can do to prevent disease problems is to select varieties with resistance, and one of the best tools available for matching varieties to a particular field is the Cooperative Extension Service's SOYVA computer selection program.

Disease ratings are a key factor considered by SOYVA when the program selects the best adapted varieties for a field.

Disease ratings for the different varieties available to Arkansas growers are also included in the UA publication, Results of the Arkansas Soybean Cultivar Disease Screening Program, published the first of each year.