Many producers are growing non-GMO corn for niche markets, including distillery and food-grade uses. Non-GMO corn is very susceptible to damage by European corn borer (ECB) and needs to be scouted periodically during ECB first and second generations. Generally, corn planted early is more susceptible to attack by first generation ECB, while later plantings are more susceptible to later generations in mid- to late summer. ECB feeding may cause physiological yield losses with smaller ears produced or harvest losses due to stalk breakage or ear drop.
From early to mid-June, corn should be scouted for ECB on a weekly basis, with more attention given to early-planted fields. To scout a field, randomly select and examine 20 consecutive plants in each location in the field. Look carefully into whorls and count the number of plants showing fresh “shot hole” (window pane) damage on the leaves. Small areas of fresh surface feeding may be seen before “shot holes” appear. Pull out the whorls of two damaged plants from each location and carefully unroll them, looking for small, whitish borers with distinct heads (black). If damage is found, and larvae are not found when unrolling these leaves, the larvae may have already tunneled into the stalk. Once in the stalk ECB cannot be controlled with insecticides.
Control should be considered if 50% of the plants show “shot hole” or “window pane” feeding damage, and larvae are still present in the whorl. Treatment may be justified for popcorn and seed corn fields if 25% or more of the plants are infested. Once larvae have bored into the stalks, treatment will not be effective. Sprays should be directed over the whorl. For the second generation, treatment is suggested if egg masses average one per plant and egg hatch has begun or if 50% of the plants inspected have live larvae feeding on the leaves or tassels, in the leaf axils, or behind sheaths. If scouting indicates that half of the larvae have already entered the stalk, insecticide treatment is not recommended.
Ric Bessin, Extension Entomologist