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European Corn Borer Scouting (07/27/17)

With more non-Bt corn planted this year, it is important to scout corn fields for European corn borer. Limited spraying for corn borer has been reported in the Valley City area.

European Corn Borer Scouting

With more non-Bt corn planted this year, it is important to scout corn fields for European corn borer. Limited spraying for corn borer has been reported in the Valley City area. Corn borer moths of the single generation should be emerging in late July into August. Look for egg masses, active larval feeding (shot-holing) in leaves, and the presence of frass. Egg masses look like fish-scales and are white to cream colored. Each egg mass contains about 20 to 30 eggs. Just prior to hatching, the black heads of the larvae become visible through the shell; this stage is referred to as the "black-head" stage. Full-grown larvae of the European corn borer are about 1 inch long, have a black head, and are gray to creamy white with spots.

Observing moth activity around field margins or within the field may alert you to developing infestations.

When larvae are about 10 days old, they reach a length about equal to the diameter of a dime and begin to tunnel into the midvein of the leaf, then burrow into the stalk. Foliar insecticides must be applied before larvae bore into the corn plant where they are protected from insecticides.

For economic thresholds, use the following table for making a decision about insecticide application.

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Janet J. Knodel

Extension Entomologist

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