Black cutworm adults (moths) were caught in pheromone traps across Iowa throughout much of April. Two major flights occurred in mid-April: the first during the nights of April 15 and 16 and the second four nights later. Moths were captured across Iowa during both flight events. Remember that having moth flights does not mean that a given field or area will have damaging black cutworm populations. From these observations, the likely first cutting dates can be projected for seedling corn across Iowa. Based on current temperatures and predicted temperatures over the next 3 weeks, the first cutting of corn is anticipated on May 15 in southwestern Iowa, on May 16 in a band from west central to southeastern Iowa, on May 17 in northwestern through central Iowa, and on May 18 in north central and northeastern Iowa (see map). These projected cutting dates are based on heat accumulations as of May 4 and on average accumulation of degree days between then and the projected date. Unseasonably warm or cold temperatures could accelerate or delay, respectively, this prediction by a day or two.
Because there have been additional moth flights since those key mid-April flights, cutting from black cutworms could be expected to extend over a long period. If you are scouting after the start dates for your area, caterpillars of several sizes could be feeding 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 pinhole feeding, only cutting; so, a treatment based only on these small holes may not be the most judicious and economical decision.
This article originally appeared on pages 66-67 of the IC-490 (8) -- May 12, 2003 issue.