As most people know, mild winters enhance the survival of flea beetles and increase the potential for the occurrence of Stewart's bacterial wilt. The bacterium that causes Stewart's wilt, Erwinia stewartii, overwinters in the soil and plant debris, as well as within flea beetles. As many as 20% of the emerging corn flea beetle adults in the spring may be infected with the bacteria. Flea beetles transmit the bacteria when they feed on corn seedlings. Although most commercial field corn hybrids are resistant to the wilt phase of Stewart's disease, symptoms of the disease may be visible. The disease is much more important for producers of seed corn and sweet corn who understand the risk, especially after a mild winter.|
We use the sum of the monthly average temperatures of December, January, and February as a "predictor" of the potential for flea beetle injury and development of Stewart's bacterial wilt. The sum of the average temperatures for these 3 months dictates the potential for flea beetle injury and Stewart's wilt as follows:
· less than 90°F--low potential
· 90100°F--moderate potential
· more than 100°F--high potential
Figure 1 (provided by Bob Scott, Illinois State Water Survey) shows the sum of the monthly average temperatures for December 2001 and January and February 2002. The news is not encouraging, but I doubt that it's surprising to most of us. The potential for flea beetle injury and Stewart's wilt in the spring of 2002 is high throughout the southern two thirds of the state.
Please understand that these "predictions" are predicated on the numbers of flea beetles that have overwintered, and these numbers are not known. Nevertheless, these guidelines based on winter temperatures at least offer an alert.
Entomologists and plant pathologists will write more articles about flea beetles and Stewart's bacterial wilt as the growing season begins in earnest. In the meantime, let this information serve as a forewarning.--Kevin Steffey