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Soybean stem canker will be problem in 2005

Arkansas farmers are concerned about Asian soybean rust, but Terry Kirkpatrick cautions farmers not to forget about stem canker, a devastating disease that's been around since 1984.

Stem canker hasn't been a real problem for farmers since 1989 and 1990 when the University of Arkansas advised them to switch to less susceptible varieties.

“We don't want to forget everything we've learned over the years in our concern over soybean rust,” said Kirkpatrick, a plant pathologist for the UA Cooperative Extension Service.

“This disease is alive and well in the state,” Kirkpatrick said. “We forgot about stem canker, and it came back to remind us in 2004.”

Kirkpatrick characterized the 2004 growing season as the most perfect season for soybean canker since 1989. Frequent rains splashed the overwintering fungus onto the leaves of young plants.

“We've been setting ourselves up for this problem,” Kirkpatrick said.

“You might have had a few plants die out in a field, but you were too busy cutting rice. We also have short memories, and there's always a new crisis to worry about. We began ignoring disease ratings put out by the Extension service.”

He said some farmers may have decided that since they hadn't seen stem canker in years, maybe it was safe to plant susceptible or moderately susceptible varieties.

Because the disease has no symptoms at the time of infection, stem canker is a frustrating disease, Kirkpatrick said. He said farmers usually don't have a clue that they have a problem until it has “blown up in a field” during the reproductive stages.

“The plants get it during the early vegetative growth stages. This pathogen remains latent in the plant with no symptoms for a couple of months in the summer until sometime after the reproductive stage kicks in.

“You can conceivably spend all the money you had planned to spend on the crop thinking it's healthy, then over the next month see stem canker take you to your knees.”

If it's a susceptible variety, a field can be devastated in a few weeks.

The key to controlling the disease in 2005 is using cultivars that are less susceptible. “We have an array of good to moderately resistant varieties to pick from. If you've ever had stem canker, don't plant susceptible varieties. It doesn't go away.”

Some cultural practices can help, he said, but don't count on them without also using a good cultivar. He doesn't think changing planting dates will help.

He said the UA Southwest Research and Extension Center at Hope, Ark., has screened 300 or so varieties for stem canker every year since 1990. That information is available through Extension's Soybean Update, and it's built into the SOYVA computer program.

“The average yield for resistant varieties was 40 bushels; the average yield for non-resistant varieties was 28. There are plenty of good varieties to choose from.”

Kirkpatrick said spraying a fungicide has never been effective in controlling stem canker because, when farmers find it, it's long past the time for it to do any good.

Meanwhile, farmers must pay more attention to what's going on in the fields.

Lamar James is an Extension communications specialist with the University of Arkansas.

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