Mid-June is the time to begin checking for small grasshopper nymphs in and around the home garden. Grasshoppers are an occasional pest and the number varies greatly from year to year and from place to place. Abundance is determined by several factors, especially the weather.
The grasshoppers commonly found in Iowa gardens spend the winter as eggs in the soil. The female deposits eggs in the soil during late summer. Most eggs are laid in turfgrass or other sod areas.
Grasshopper eggs begin to hatch in mid-June to early July. The tiny grasshopper nymphs (immatures) feed on tender grass and succulent plants in the area where they hatched. As they grow and develop they spread to adjacent areas (into tilled garden areas, for example) and feed on an increasingly-diverse variety of plants. Grasshopper nymphs live for 40 to 60 days after which the adults appear and continue feeding until they are killed by cold weather.
Damage caused by grasshoppers appears as irregular holes at the edge of plant leaves. As grasshoppers grow they may eat larger portions of infested leaves, and may eventually destroy every green plant in the area.
Several natural controls reduce grasshopper populations in most years. Exceptional populations of grasshoppers occur when weather, predators, parasites and pathogens combine in a way that allows more-than-usual numbers of eggs and nymphs to survive.
Applied controls include mechanical removal (which is not widely practiced nor practical) and insecticide sprays. Applied natural controls such as the microsporidian disease (Nosema) are not effective in garden situations.
The most effective use of insecticides is to treat the hatching areas (e.g, turfgrass, waterways, roadside ditches, fencerows) when grasshoppers are still small. Larger grasshoppers are much more difficult to control. Infested plants can be treated but slow control usually means damage will continue until grasshoppers already on the plants have consumed a sufficient quantity of the insecticide residue. Migration of grasshoppers from the surrounding area also limits the effectiveness of spraying just the garden plants. Insecticide sprays are more effective than dusts.
Insecticides for grasshopper control include permethrin, Sevin, malathion and rotenone. Check the label to make sure the crop you intend to spray is listed on the label directions. Apply at only the rate listed on the label and repeat no more often than specified. Check harvest waiting restrictions for the waiting period between application and harvest.
This article originally appeared in the June 21, 2002 issue, p. 86.