Black cutworm moths were caught in pheromone traps across Iowa throughout much of April. Several "waves" of moths flew in from southern states during April 8-12. Captures of these early moths primarily occurred in the central and southern Iowa counties. Another wave of moths flew farther north, beginning on April 14, with many traps catching moths during April 15-23. From these collections, we can project the likely first cutting dates of seedling corn across Iowa. Based on current temperatures and predicted temperatures over the next 3 weeks, we anticipate the first cutting of corn on May 10 in southern Iowa (see map). Unseasonably warm or cold temperatures could accelerate or delay, respectively, this prediction by a day or two.
Because there were several successive waves of moth flights this year, cutting from black cutworms could be expected to extend over a long period. Feeding by caterpillars of several sizes could be expected in the same field. Before cutting occurs, small cutworms often eat pin-sized holes in the leaves. Some producers may decide to mix an insecticide with a herbicide application when they see this injury. Before the insecticide is included in the application, confirm that black cutworms are the insects in the field that are responsible for the leaf-feeding injury. There are no economic thresholds for pin-hole feeding, only cutting, so a treatment based only on these small holes may not be the most judicious and economical decision. Next week, we will have information on economic thresholds and insecticide options.
Predicted first cutting dates in corn from black cutworms.
This article originally appeared on page 60 of the IC-488 (7) -- May 6, 2002 issue.