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Differential Grasshopper


Image Copyright Iowa State University

Description:

Most grasshoppers are general feeders on the leaves and stems of many types of plants and cause complete destruction of the plant. Large numbers of grasshopper nymphs can develop in tall weedy areas, attracting little attention. However, when they become winged adults, they can fly and disperse greater distances, and suddenly appear injuring field crops.

Conditions:

July to September. Estimate the size of a grasshopper infestation by surveying for nymphs or adults with the "square foot method." Count the number of grasshoppers that hop or move within a square foot area. Then take 15 to 20 paces and sample another square foot area. Make 18 samples in all. Then add the numbers from each sample and divide the total by two to obtain the number of grasshoppers per square yard. If most grasshoppers you see are first to third instar (wingless and generally less than 1/2 inch long), divide the number by three to give the adult equivalent. Count fourth instar and older nymphs as adults.

Management:

Biological Control Grasshoppers have many natural enemies that help control their populations. A fungus, Entomophthora grylli, often kills many grasshoppers when the weather is warm and humid. Other natural enemies include nematodes called hairworms and insects that feed on grasshoppers, such as the larvae of blister beetles, bee flies, robber flies, ground beetles, flesh flies and tangle-veined flies. Mechanical Control Eliminate sites where they might deposit eggs. Grasshoppers prefer undisturbed areas for egg laying, so tilling cropland in mid- to late summer discourages females. Tilling may reduce soil moisture and contribute to erosion, but those disadvantages must be weighed against potential grasshopper damage to the next crop. Cultural Control Controlling summer weeds in fallow fields has two benefits: 1) If grasshopper eggs are already in the field, there will be nothing for nymphs to feed on when eggs hatch. 2) Fields will not be attractive to egg-laying adults because there is nothing on which to feed. Also eliminate tall grass and weeds from around any plants you wish to protect (crops, trees and gardens). This makes the area less attractive to grasshoppers and makes it easier for birds to prey on grasshoppers. Monitoring Populations Start watching for grasshoppers early in the season and begin control measures while grasshoppers are still nymphs and still within the hatching sites (roadsides, fencerows, etc.). Treating grasshoppers early means: 1) having to treat fewer acres and use less insecticide 2) killing grasshoppers before they cause extensive crop damage 3) killing grasshoppers before they can fly, migrate and lay eggs 4) smaller grasshoppers are more susceptible to insecticides than larger ones

Sources:

Texas A&M University
ISU

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