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Grasshoppers in 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. Treat a wide border around the garden or vegetable field to prevent migration into the crop area. The last line of defense is to spray infested plants which can be a slow and repetitive process. Damage will continue until grasshoppers on the plants have consumed a sufficient quantity of the insecticide residue and migration of grasshoppers from the surrounding area means treatment will have to be repeated every 3 to 5 days. Keep in mind insecticide sprays are more effective than dusts and small grasshoppers are easier to kill than adults.
Insecticides for grasshopper control include pyrethroids such as bifenthrin, permethrin, cypermethrin, cyfluthrin and lambda-cyhalothrin, and Sevin, or malathion. 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.
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