In years past, the European corn borer was the most important pest of sweet corn, as well as being a pest of peppers and other vegetables. Since the advent of Bt field corn, the overall population of corn borers has been dramatically suppressed, so far that we often forget about it being a pest of sweet corn. However, occasionally the corn borers like to remind us that they are still around and can still be damaging to our crops. These outbreaks usually occur in the northern part of the state, often in areas where the landscape is not dominated quite as much with field corn and soybeans. Corn borers have a broad host range, so diverse habitats provide them with a choice of suitable foods.
Management of corn borers in sweet corn is relatively easy. As your sweet corn approaches tasseling, look for corn borer feeding and confirm that borers are present by looking for them in the rolled up leaves. The optimal time for treatment is just before the tassels start to emerge. An insecticide spray over the top of the plant will funnel the insecticide down into the whorl of the plant where the borers are hanging out. There are lots of good choices of insecticides for corn borer control, both conventional and organic. See the Midwest Vegetable Production Guide for details. Remember that we have not seen resistance to pyrethroids in corn borers like we have in corn earworms.