There's good news and bad news on the soybean disease front. The good news is that two serious soybean disease problems, sudden death syndrome (SDS) and stem canker, can be controlled by planting varieties that are resistant to the diseases.

The bad news, for some farmers, is that varietal resistance is presently the only effective method of controlling the two diseases. That can be a problem when other field conditions call for planting varieties that are not resistant to SDS or stem canker, Dr. John Rupe, University of Arkansas plant pathologist, said recently.

"We are working on the problem from several directions," said Rupe, a member of the UA soybean disease research team that also includes Drs. Terry Kirkpatrick, Robert Robbins, Bob Riggs, Rose Gergerich, Larry Purcell and Clay Sneller. They are working on a variety of projects supported by the Arkansas Soybean Promotion Board.

"We are rating varieties for resistance in the statewide Soybean Variety Testing Program directed by Don Dombek and in a very effective stem canker disease nursery managed by Dr. Terry Kirkpatrick at Hope (Southwest Research and Extension Center).

"We are also studying mechanisms of infection and resistance to provide information a breeder might use to develop more resistant cultivars and to develop other practical methods of controlling these diseases," Rupe said.

Fungicides have been shown to be effective against SDS and stem canker, but they can't be used because there is no way to tell when plants become infected in the field. When symptoms begin showing, it is too late for fungicides to help, Rupe said.

In one study, a fungicide is being applied up to two weeks before and after plants are inoculated with the stem canker fungus. The results will help identify a window of opportunity for eventual use of fungicides when infection mechanisms are better understood.

A major long-term objective of several studies is to understand the role of the environment on the diseases, Rupe said. "We are looking at the infection process to try to find ways to intervene at different stages in the process."

Some evidence suggests that the fungus may be building up in the soil around the roots before moving into the roots. "This implies that the fungus may be susceptible to a cultural practice or biological control agent that could work in the soil before the plant is infected," he said.