2/3/00

Contacts:
Forrest Nutter, Plant Pathology, (515) 294-8737
Ed Adcock, Agriculture Information, (515) 294-2314

WORST YEAR EXPECTED FOR STEWART'S DISEASE

AMES, Iowa -- The worst year ever for outbreaks of Stewart's disease in Iowa cornfields will likely give way for another record outbreak next crop season, according to Iowa State University researchers.

A computer model developed at ISU predicted 1999 would be a bad year for the disease, which is also called Stewart's wilt. An inspection of 1,317 seed corn fields last summer and fall found the disease in 58 percent of them. The previous high was 25 percent the year before.

"It just exploded last year," said Forrest Nutter, plant pathologist who led the development of the computer model.

The disease is caused by a bacterium transmitted by corn flea beetles. The disease isn't a problem in many fields, but it can damage susceptible inbreds used to produce seed corn and sweet corn. In severe cases, hybrid corn yields may be reduced.

Seed companies suffer when they try to export seed from infected fields. Many countries restrict seed when it comes from fields where Stewart's disease was detected.

Mild winter weather, especially during December, January and February, are favorable for flea beetle survival in soil. Studies of the flea beetle also lead Nutter to predict another outbreak next year.

"Between 55 and 75 percent of the flea beetles studied last fall were infected with the bacterium. The year before we found about 15 percent were infected," he said.

Nutter said seed companies could use the information generated by the computer model to help decide where to plant and whether to use insecticides to manage corn flea beetles.

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