Grasshoppers Are Hatching

Grasshoppers have started to hatch and now is the time to begin scouting your crops and rangeland.

Grasshopper Life Cycle

In the fall, adult grasshoppers deposit their eggs in the soil where they overwinter and begin to hatch from May-July. Juvenile grasshoppers develop through five nymphal instar stages (30-40 days) before developing into an adult with fully formed wings. Adults live for 40-60 days. There are a few species of grasshoppers that overwinter as nymphs; however, these species are not economically damaging.

Management

The majority of management options for grasshoppers rely on insecticide applications based on scouting and threshold of the crop. Cultural and biological control options are not generally effective.

Scouting

Crop fields should be scouted at least once a week. High nymphal densities can cause severe defoliation, however newly emerged grasshoppers do not need to be controlled unless their population is at a threatening level. Grasshopper numbers can be estimated using the square foot method by counting the number of grasshoppers in a visually estimated square foot, and randomly repeating it 18 times while walking in a transect, tally the number and divide by two to get the number per square yard. When grasshoppers are in high numbers, it can be difficult to do the square foot method. Four 180º sweeps with a 15-inch net is equivalent to the number per square yard.

Control

It is easier and more economical to control grasshoppers while they are in their nymphal stages, because they can be killed before damaging crops, treatment prior to maturity can prevent egg deposits, and smaller grasshoppers are more susceptible to insecticides.

Control in Crops

For a list of insecticide options by crop, see the North Dakota Field Crop Insect Management Guide, available online or at the Extension Office.

The following table shows rates based on grasshopper nymph and adult counts. Newly emerged grasshoppers do not usually need to be controlled unless the population is at the “threatening” level or action threshold.

Control on Rangelands

A number of 15-20 grasshoppers per square yard is the economic threshold for treatment of grasshoppers on rangeland. These densities can result in up to 200-500 pounds of forage lost per acre. Reduced Agent and Area Treatment strategies (RAATs) can be used on rangeland to reduce control costs. For more information on RAATs and rangeland grasshopper control, visit https://www.ars.usda.gov/ARSUserFiles/30320505/ARS-PPQ%20Grasshopper_03-29-22.pdf.