Grasshoppers and their damage are abundant in several areas of the state. Extension specialists in field crops Joel DeJong, John Creswell, and Paul Kassel report damage to corn border rows in western, northwestern, and central Iowa. The grasshopper photographs, taken north of Council Bluffs in Harrison County on August 19 show the damaging nature of these grasshopper populations.
Grasshopper densities of 10-20 per plant were common and they had heavily defoliated plants 5-8 rows into the field. Some corn ears were crawling with 10-12 grasshoppers and often half of these were feeding on exposed kernels. All ears in the first three rows had exposed kernels with damage or complete kernel removal. Ears that I measured had 13-20 percent of the kernels removed. This kernel loss, coupled with the physiological damage to the grain from the loss of leaves, will translate into a hefty yield reduction at the end of the season.
Grasshopper damage can be stopped with the proper application of a registered insecticide. Determine how many rows are infested with grasshoppers and spray only those rows. You should not expect the insecticide to last forever in a field. Additional grasshoppers may migrate later from grassy or weedy margins back into the corn, but most of the population should be controlled with one spray application, especially if the field margins are included in the effort. For a list of registered insecticides for grasshoppers in corn, see the July 15 issue of this year's ICM newsletter, page 124.
This article originally appeared on pages 159-160 of the IC-476(23) -- September 3, 1996 issue.