Several reports have been received this week indicating that European corn borer hatch is under way. Reports included observations of heavy moth flights and feeding in cornfields by both first and second instars. Dennis Dixon, Hartung Brothers Inc., believes the first corn borers have hatched in the fields around Havana; and Mike Roegge, unit educator in crop systems, Adams/Brown counties, found pinhole feeding and first and second instars in a plot he was scouting. Kevin Black, Growmark, reported first and second instars, fresh egg masses, and moths in both Randolph and White counties last week. A 50% to 60% infestation was reported by Randy Mcelroy in an April-planted field in Mt. Erie. Egg masses and first, second, and even a couple of third instars were found.
Survivorship of corn borer larvae during mating, egg laying, and early larval development is very dependent on weather. Both drought and excess moisture affect early larvae survival. Table 1 presents the effects of drought stress and excess moisture on the survivorship of first-generation larvae on a susceptible corn hybrid. In this study, 2 days after hatch, excessive moisture caused 67.5% mortality, whereas drought stress caused only 21.5%. Six days after hatch, drought stress caused 56.7% mortality, and moisture inundation caused 87.5%.
Questions remain on how corn borer populations have been affected by the recent storms and rain; as moth flights continue, it's important to scout for larvae, especially if corn is less than 15 to 18 inches tall. Detailed information on scouting for European corn borers was included in issue no. 11 (June 6, 2003) of the Bulletin). Also included was the management worksheet for first-generation corn borer and the insecticides labeled for use on European corn borer. As always, continue to report any findings and stay tuned for future updates.--Kelly Cook