WOOSTER, Ohio -- Southern Ohio's corn crop may face a high risk of Stewart's bacterial wilt and leaf blight this growing season. The disease is caused by a bacterium carried and spread by adult flea beetles.
Based on the flea beetle index, conducted by Ohio State University Extension and Ohio Agricultural Research and Development Center specialists this winter, flea beetle populations are predicted to be high in southern Ohio, and low to moderate in northern and west central Ohio. As a result, cornfields in southern counties could be at a greater risk for the disease.
"The occurrence of Stewart's bacterial disease is totally dependent on the level of bacteria-carrying flea beetle survival over the winter," said Ron Hammond, an OSU Extension entomologist. "For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters."
The flea beetle index is calculated as the sum of the average temperatures of December, January and February. Index values less than 90 indicate a negligible disease threat, 90-95 indicates low to moderate levels, 95-100 indicates moderate to severe, and values over 100 indicate a severe disease threat.
The results covered six locations: Hoytville with a value of 84.4; Wooster with a value of 88.4; Ashtabula with a value 87.4; South Charleston, with a value of 90.4; Jackson with a value of 99.7; and Piketon with a value of 100.3.
"These values are very similar to those from last winter. However, when comparing the temperatures last year to the past three months, we see a very different picture," said Pierce Paul, a plant pathologist with the Ohio Agricultural Research and Development Center. "Last year, December and January were relatively warm, while February was an extremely cold month. This year, these three months have, on average, been more typical of the temperatures one would expect, without any month being neither extremely warm nor cold."
The message for growers: Scout for flea beetles this spring, especially if you are planting a hybrid that is susceptible to Stewart's wilt.
"Beetles survive in the soil and emerge when soil temperatures warm to about 65 degrees (Fahrenheit). The flea beetle is a small, black, shiny insect. Once you know it, you can't miss it," said Paul, who also holds an OSU Extension appointment. "Contact your OSU Extension county office 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.
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.
To learn more about Stewart's wilt, log on to OSU Extension's Ohioline at http://ohioline.osu.edu/ac-fact/0037.html, or OSU Extension Agronomic Crops Team Web site at http://agcrops.osu.edu/.