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Western bean cutworm is a pest that has increased in range and importance in western and northern Iowa in the last 3—4 years. Damage to field corn results from larvae feeding in the ears, and losses come from both the direct loss of kernels, and therefore grain yield, and in secondary damage from subsequent infection by ear rot organisms and other scavenging insects.
There is one generation per year, and management centers on detection, population monitoring, and appropriate and timely treatment. Adults emerge in middle- to late-July, depending on accumulated heat, and females begin egg laying immediately following mating. If an insecticide treatment is warranted, it must be made in the narrow time window between larval hatch and movement down the silks to the developing kernels. Field scouting should begin when the first moths are captured in an area. Examine upper surfaces of leaves for egg masses and also young tassels for young larvae. University of Nebraska (UN-L) guidelines suggest a scouting regimen that includes examining 10 consecutive plants in random locations of each field. As few as five locations per field may be sufficient to adequately estimate the general population in a field if infestation levels are high (greater than 2 in ten plants infested) or extremely low (zero in ten plants infested.) UN-L suggests considering an insecticide application if 8% of corn plants have egg masses and, or small larvae. They suggest the following: “If an insecticide treatment is made, timing is critical. If the larvae have hatched, insecticide treatments should be made after 95 percent of the tassels have emerged, but before the larvae have a chance to enter the silks. Once larvae move to the silks, insecticide control is more difficult. If the larvae have not hatched and plants are tasseled, the application should be timed for peak larval hatch. (note: Eggs turn purple about 24 hours before larvae hatch.)”
Source: Nebraska Cooperative Extension NebGuide, G98-1359, Revised March 2002.
