Corn flea beetle survival and potential for Stewart’s wilt
The leaf blight phase can occur at any time during the growing season, but often does not appear until after tasseling. Lesions are typically long and narrow, with greenish-yellow streaks and irregular or wavy-margins. Lesions will become straw-colored, and infected leaves may die prematurely. Hybrids with resistance to Stewart’s wilt may have smaller lesions that are limited to the tissue surrounding the feeding site of the beetle. These lesions can be confused with the fungal diseases gray leaf spot or northern corn leaf blight. Stewart’s wilt is also commonly confused with another bacterial disease, Goss’s wilt. One way to differentiate between these diseases and Stewart’s wilt is to look for the beetle feeding scars associated with Stewart’s wilt.
Management decisions made now should be based on the corn’s susceptibility to the disease and anticipated risk. With virtually all corn seed treated with insecticide (Poncho or Cruiser), the only decision to be made is whether a low or higher insecticide rate should provide sufficient protection. Those decisions have likely been made months ago, and even the lowest available rates of seed treatments (Poncho 250) are expected to provide protection from emergence to 2-leaf corn, whereas the higher rate (eg. Poncho 1250 and Cruiser 1.25, also called the “rootworm rate”) should protect corn through the 5th leaf stage. If seed-applied insecticide is not an option, broadcast application of foliar insecticides at the time when corn spikes should provide 7-10 days of residual protection from beetle feeding.