Stewart’s wilt may hit Ohio in 2007

COLUMBUS – Cornfields throughout southern Ohio might be at risk this growing season for Stewart’s bacterial wilt and leaf blight – a corn disease caused by a bacterium carried and spread by adult flea beetles.
According to the flea beetle index, southern Ohio may be at moderate to severe risk from Stewart’s wilt. The disease threat for northern and central Ohio is low to negligible.
The model uses the sum of average temperatures for the months of December, January and February to assess flea beetle survival and disease threat levels.
Caution. “Despite the assessment, we are advising growers to exercise caution when relying solely on the flea beetle index due to the atypical weather conditions we had in December, January and February,” said Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center.
“December and January were very mild and it was very cold in February for a relatively short period of time. If February’s temperatures had been normal or mild, our risk levels would have been much higher.”
Paul, who also holds an Ohio State University Extension appointment, recommends growers still scout their fields in the spring after corn emerges, especially if they’ve planted hybrids susceptible to Stewart’s wilt.
“Beetles survive in the soil and emerge when soil temperatures warm to about 65 degrees. The flea beetle is a small, black, shiny insect. Once you know it, you can’t miss it,” said Paul.
Count. He recommends growers do a count of the number of flea beetles per plant, and contact OSU Extension if you have questions or need treatment recommendations.
For those growers wanting to take preventive action against the flea beetle, commercially applied insecticide seed treatments Cruiser and Poncho or the grower-applied products Concur and Latitude are labeled for flea beetle control.
The risk of Stewart’s wilt depends on the number of beetles carrying the bacterium that survived the winter.
The greater the problems with Stewart’s wilt the previous year and the more overwintering beetles may be carrying the disease, the greater the risk of Stewart’s wilt in the following season’s crop.
The good news, said Paul, is that Ohio faced few Stewart’s wilt outbreaks last year.
Characteristics. Stewart’s wilt is characterized by two major disease phases. One phase is seedling blight. Young plants develop pale green to yellowish streaks on the leaves.
These young plants usually wilt and die and those that survive are stunted and usually produce no ears.
The other phase is the leaf blight stage. Leaf blight is recognized as long, pale green streaks on leaves. As the streaks enlarge, portions turn pale yellow and eventually become brown. Streaks may run the entire length of the leaf.
A few characteristic lesions may be seen early in the season, but numerous lesions are usually not detected until after tasseling.
Learn more about Stewart’s wilt at http://ohioline.osu.edu/ac-fact/0037.html or at the OSU Extension Agronomic Crops Team Web site at http://agcrops.osu.edu/ .