Mild winter increases Stewart’s wilt

WOOSTER, Ohio – Southern Ohio’s corn crop may be facing a high risk of Stewart’s wilt bacterial disease this growing season.
Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said because of Ohio’s mild winter, higher populations of flea beetles (the insect that transmits the bacterium) may have survived, increasing the chances for the spread of the disease, which causes both seedling wilt and leaf blight.
Index. Ohio State specialists use a flea beetle index – the sum of the average temperatures for December, January and February – as an indicator of high flea beetle populations and subsequent risk of Stewart’s wilt.
Index values less than 90 indicate negligible disease threat, 90-95 indicates low to moderate levels, 95-100 indicates moderate to severe, and values over 100 predict severe disease threat. For locations monitored in southern Ohio – Columbus, Oxford, Jackson and Piketon – index values were over 100.
Other locations throughout northern and west central Ohio indicated low to moderate disease risk.
“The only portion of the state that is at risk is southern Ohio,” Paul said. “One of the good things is that we know from last year we didn’t have a disease problem in the state. So even though we may have high beetle populations, we are coming off a year with low Stewart’s wilt, so the beetles are less likely to be carrying the disease.”
Scout the fields. Although the flea beetle index has been a relatively good predictor over the years, Paul still recommends that growers scout their cornfields for the presence of flea beetles, especially if they have planted a hybrid that is susceptible to Stewart’s disease.
For growers wishing 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.
For information on the flea beetle and Stewart’s wilt, go to http://agcrops.osu.edu and click on “Diseases” under Crop Info on the left side of the page or refer to OSU Extension Fact Sheet AC-0037-01 at http://ohioline.osu.edu.