Issue No. 12, Article 7/June 11, 2004
Some Significant Grasshopper Activity Noted
Several FS employees have reported to Kevin Black (Growmark, Inc., Bloomington) that grasshopper densities are "surprisingly high" in some areas, and injury in both corn and soybean fields has been observed. Dale Burmester, crop specialist with Gateway FS in Redbud (Randolph County), reported severe grasshopper injury to soybeans in his area.
The primary species of grasshoppers that can cause problems in Illinois during most years are the differential grasshopper (Melanoplus differentialis), the migratory grasshopper (M. sanguinipes), the redlegged grasshopper (M. femurrubrum), and the twostriped grasshopper (M. bivittatus). All of these species overwinter as eggs in clusters in the soil, usually in uncultivated areas such as ditches, roadsides, fencerows, waterways, and pastures. The nymphs hatch in May and June, depending on the species (twostriped, migratory, redlegged, and differential, from earliest to latest), and begin feeding first in noncrop areas. However, if densities are high, as has been reported, the nymphs will move into the edges of corn and soybean fields quickly. As the grasshoppers grow and other nymphs emerge, the injury to crops gets progressively worse.
Grasshopper nymphs on a culvert in a roadside (University of Illinois).
Severe grasshopper damage to corn in southern Illinois in 2002 (photo provided by Dennis Epplin).
There are two schools of thought regarding management of grasshoppers: (1) control the nymphs in field edges and noncrop areas before they cause extensive damage; (2) wait to see if pathogen cause epizootics that cause grasshopper populations to "crash." Both approaches have benefits and limitations, and deciding between them depends on current and projected field and weather conditions and grasshopper densities. Our advice is to determine the location of most of the nymphs (staying in noncrop areas or moving into corn or soybean fields), assess the intensity of the infestation, and act accordingly. Treatment thresholds for grasshoppers along field edges are notoriously unreliable. In other words, use your instincts.
Table 2 shows products labeled for control of grasshoppers in noncrop areas and in corn and soybean fields. If you determine that an insecticide is necessary, please follow all label directions and precautions. --Kevin Steffey