Flea bitten
By James D. Ritchie
Flea beetles may hop on your crop. Or did cold winter temperatures keep beetles at bay this year? Scout to be sure.
Flea beetles are small, dark-colored jumping insects that overwinter as adults, ready to attack corn as soon as the plant emerges.
“Mild temperatures during December, January and February increase the potential for high populations of flea beetles in most regions of Missouri,” said Wayne Bailey, University of Missouri extension entomologist. “In early spring, flea beetles can move to seedling corn and feed on young plants from the time corn plants emerge through about the four-leaf stage of growth.”
Adult beetles strip the chlorophyll or green tissue from corn leaves, leaving behind “window panes” or translucent areas on leaf surfaces.
“The damage often is seen as translucent lines or tracks that run parallel to the veins of a corn leaf,” Bailey added. “Heavy beetle infestations can cause plants to look wilted and tattered—similar to damage caused when seedling corn is blasted by blowing sand.”
Corn (or maize) flea beetles typically cause the most injury. Infestations usually are most severe in springs following mild winters, which allow more adult beetles to survive—especially when cool temperatures or dry weather slow the growth of corn plants.
Bailey uses a winter-temperature model to try to predict the severity of flea beetle infestations. He adds together the average daily winter temperatures (for December, January and February), as recorded at 17 UMC Commercial Agriculture weather stations.
In other words, the daily high and low temperatures are averaged, and then these daily temperatures are averaged for the month. The average temperatures for the three winter months are added together. If the average monthly temperatures add up to 90 degrees or less, the potential for flea beetle damage is low. If the total is between 90 and 100 degrees, you can expect moderate damage. And if the three monthly averages total 100 degrees or more, there’s risk of heavy flea beetle damage.
“The model is a good guide to follow, although other factors can influence beetle survivability,” said Lyndon Brush, MFA staff agronomist. “For example, a blanket of snow can insulate soil and keep it relatively warm and make it more likely that adult beetles will live through a cold snap. Bare ground makes it more likely that beetles will be killed when temperatures dip.
“Newer seed treatments, such as Poncho, give some systemic suppression of flea beetles,” Brush added. “But it’s a good idea to check plants from the time corn emerges, especially if you aren’t using a newer seed treatment.”
“The economic threshold for flea beetles in field corn is an average of five or more beetles per corn seedling, up through the fourth-leaf stage,” said Bailey. “To scout for flea beetles, examine corn plants for feeding damage and estimate the average number of beetles per plant. Scouting is more effective in early morning or late afternoon, by walking slowly through the field and counting beetles as they feed.
If an economic population of flea beetles is found, several foliar-applied insecticides are labeled. Check with your county extension office or MFA Agri Services Center. Notice that most of the insecticides labeled for flea beetle management are restricted-use pesticides.
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