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 European Corn Borer update Minimize
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Posted by: WCM Staff 6/23/2008 2:54 PM
Degree Day accumulations suggest the southern ½ of Wisconsin is at, or just past peak European corn borer flight and the most opportune treatment timing (if needed) may be starting in southern Wisconsin. Spot-check earliest planted corn because it is more attractive to female first generation European corn borer moths to lay eggs.

European Corn Borer update

Bryan Jensen, UW Madison IPM Program

Degree Day accumulations suggest the southern ½ of Wisconsin is at, or just past peak European corn borer flight and the most opportune treatment timing (if needed) may be starting in southern Wisconsin. Spot-check earliest planted corn because it is more attractive to female first generation European corn borer moths to lay eggs. Additionally, late planted corn often has high larval mortality due to elevated concentrations of DIMBOA.  DIMBOA is an acronym for a naturally occurring plant defense compound which protects corn from corn borer feeding in plants under 18 inches extended leaf height. DIMBOA concentration decreases in taller corn making survival possible.
 
To get an accurate assessment of corn borer damage, examine 10 consecutive plants in 10 areas of the field for leaf feeding. Pull the whorl leaves from two infested plants in each area and unroll the leaves to look for borers. Calculate the percentage of plants with recent leaf feeding and average number of European corn borer larvae/ infested plant.  and consult the management worksheet for first generation corn borer. Current corn prices and higher applications costs make use of the first generation European corn borer worksheet important. Go to page 63 of the Pest Management in Wisconsin Field Crops—2008 bulletin available on line at http://learningstore.uwex.edu/pdf/A3646.PDF. 
 

Mortality of first instar larvae maybe  high if temperatures are extremely high or if rains are heavy. If the majority of larvae are first instars (2 mm in length) resample in a few days to verify survival before treating.  Small surviving larvae may not always be capable of chewing holes through the corn leaf and will leave a window pane appearance. Larger larvae will chew holes completely through the leaf leaving random “shotholes” and sometimes transverse holes across the leaf. Third instar larvae (3/8 long) start to burrow into the corn stalk making control making insecticidal control impractical. 
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