WOOSTER, Ohio – Growers scouting their fields this spring should be on the lookout for corn flea beetle as the relatively mild winter Ohio has experienced this year is expected to cause a moderate to severe infestation of the pest, an Ohio State University Extension entomologist said.
Corn flea beetle, which targets corn through the spread of the bacterium that causes Stewart's bacterial wilt and leaf blight on both field and sweet corn, will likely be seen throughout much of the state this year, said Ron Hammond, who also has an appointment with the Ohio Agricultural Research and Development Center.
Adult beetles that overwinter become active in the spring when the soil temperature reaches 65 degrees, and are most active on sunny, warm, windless days. Higher populations of the flea beetle survive during milder winters, such as that experienced this year, than during cold winters, he said.
Using a “flea beetle index” that calculates the average sum temperature of December, January and February to predict the likelihood of the disease threat, OSU Extension researchers have found that all areas of the state except for northern areas have indexes above 95, suggesting that the risk is moderate to severe for the pest this year.
Northern areas were found to have indexes over 90, suggesting a low to moderate risk this spring in those areas, Hammond said.
Most growers, particularly those who use transgenic hybrids, don’t have to apply additional treatments as seeds already come with an insecticide treatment applied, Hammond said.
“But growers who plant non-transgenic corn may need to consider using a commercially applied insecticide seed treatment labeled for flea beetles,” he said.
“Crop growers should scout their fields for flea beetles, especially if they have planted a hybrid that is susceptible to Stewart's disease,” he said. “Growers that have experienced the disease in past crops and are planting susceptible hybrids can mitigate the damage if they scout their fields early.”
Also, most field corn hybrids are more resistant to wilt than sweet corn, with dent corn hybrids varying greatly in their resistance to the leaf blight stage phase of the disease, Hammond said, noting that sweet corn varieties are often susceptible to wilt in the first leaf stage.
“A few are resistant by the second leaf stage and many are resistant in the third and fourth leaf stage,” he said. “Consult your seed supplier for information on resistant varieties and hybrids.”
But while the temperatures this winter might allow for an increase in corn flea beetle numbers, Hammond said that doesn’t automatically result in higher incidence of Stewart’s.
“The surviving flea beetles need to be carrying the bacterium in order to infect plants in the spring, and in order for them to acquire the bacterium, they needed to feed on diseased plants last season,” he said. “So with the level of Stewart’s disease being low during 2012, it is quite possible that beetles, even if they survived due to the mild winter, may not be carrying the bacterium.”