Grasshopper Control

Mike Schuldt
Thursday, July 30, 2020

Large numbers of grasshoppers have been spotted in Southeast Montana this summer. The best time to control grasshoppers is when they are young, before they have wings and can fly away from insecticide treatments, however we have missed this opportunity this year. For best results, organize your neighborhood or local farming/ranching community to work together to treat larger tracts of land. Treating wide areas is a key to success.

Grasshoppers are the most difficult insect to control as they are highly mobile and actively search out new food sources. This means that if you control the infestation in your yard, garden or field in a short time a new population may move in and re-infest the area.

In the late summer and fall, adult female grasshoppers lay their eggs in pods in undisturbed soil such as open fields, roadsides, weedy areas, rangelands and boundaries between open space and residential lots. The eggs hatch the following spring and immature grasshoppers, called nymphs, crawl and hop to find green plants to eat. As temperatures warm, soil moisture declines and unmanaged plants dry out. Grasshopper nymphs then move into home yards, gardens and agricultural fields to seek green forage.

There are three types of insecticide formulations to treat grasshoppers: baits, dusts and sprays. Baits are a mixture of an attractive food source, such as wheat bran, with an insecticide. Common baits contain carbaryl, a carbamate insecticide, or spores of Nosema locustae, a natural grasshopper pathogen. Baits should be spread evenly throughout the habitat and must be reapplied weekly and immediately after rain or irrigation. Baits are selective in that they only kill grasshoppers and other foraging insects (N. locustae will only kill grasshoppers).

Dusts have short residuals and must be reapplied weekly and after rain or irrigation. Both baits and dusts are easy to apply, but moderately expensive. There are numerous insecticide sprays that work against grasshoppers, including malathion, carbaryl, permethrin and bifenthrin. An insect growth regulator, diflubenzuron (Dimilin), is available for commercial-scale applications.

Sprays are less expensive than baits and dusts but require a sprayer suitable to the scale of application. Sprays will kill on contact or when grasshoppers eat the treated foliage. Check all product labels for allowed application sites. For example, some insecticides can be applied to ornamental but not edible plants.

For residential sites, apply insecticides along the borders of the properties and into the open and irrigated lands on either side of the border. There isn’t a threshold established for residential lands, but USDA recommends that treatments begin when nine or more grasshoppers are found per square yard on rangelands. A threshold for cultivated lands, including urban and agricultural, would likely be lower. If possible, apply a border treatment to all neighboring properties. For best results, work with neighbors to increase the size of the treated area.

(Mike Schuldt is the Custer County Extension Agent.)

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