Weather conditions in several areas of Nebraska in the past few years have been favorable to create grasshopper outbreaks. The fall grasshopper survey is a good indicator or possible grasshopper issues the following summer. The 2023 fall survey identified 15 counties (Fig. 1) in Nebraska with adult grasshopper numbers averaging over 15 per yard, which suggests grasshoppers may be a problem this summer.
Pasture grasshopper species that are most damaging are found in areas with less than 30 inches of annual rainfall. Western two-thirds of Nebraska falls into this rainfall category. With the occurrence of consecutive years of drought grasshopper outbreaks are possible. The past several years southwestern, southcentral, and western Nebraska has experienced below normal precipitation. This type of weather pattern can play a large role in rangeland grasshopper outbreaks.
Approximately 50 species of grasshoppers are found on rangeland in Nebraska, though generally fewer than 10 species ever reach economic levels, accounting for 95% of the damage. Grasshoppers defoliate grass by direct feeding on leaf and stem tissue and by cutting off leaves or stems.
Grasshopper Life Cycle
The developmental stages of all grasshoppers include the egg, nymphal, and adult stages. Most species winter as eggs. Normally, grasshopper eggs will remain in the overwintering stage until the ground temperature reaches 50° to 55° Fahrenheit. Newly hatched grasshoppers look like miniature adults except they lack wings, and their sex organs are not developed. As young grasshoppers grow they shed their skin (molt). Depending upon the species they might molt four to six times, with five molts being the average. The rate at which nymphs develop is influenced by temperature and food quality. Most species reach the adult stage, 30 to 50 days after hatching.
Grasshopper Impact
Grasshoppers consume up to 50% of their body weight every day in forage. A rate of just 2.7 grasshoppers per square yard equals 12,971 grasshoppers per acre.
An acre with 69.7 grasshoppers per square yardequates to the consumption of forage by one cow per day.
Economic thresholds for grasshopper densities in rangeland vary from 8 to 40 grasshoppers per square yard. The thresholds are influenced by several factors, including the cost of control product, projected forage yield, and the value of forage considered for treatment.
Grasshopper Monitoring
One of the better methods for determining grasshopper density is to count the number of grasshoppers using the square foot method. With this method sample at multiple sites about 50 to 75 feet apart. Select a point several feet away and visualize a one-foot square area around the point. Walk toward the point counting any grasshoppers you see in or jumping out of this area. Repeat 18 times, total the number of grasshoppers, and divide by 2; the resulting number will be the number of grasshoppers per square yard.
A request for technical assistance to evaluate the need for grasshopper control in rangeland may be submitted to USDA-APHIS, by contacting David Nielsen at (402) 434-2348 or by email at David.Nielsen@usda.gov
Grasshopper Control
A grasshopper integrated pest managment program called Reduced Agent and Area Treatment (RAATs) was developed by researchers at the University of Wyoming to improve grasshopper control in pastures and rangeland. Insecticides are applied in alternating strips, reducing application costs by 50 to 60% and reducing the amount of insecticide used by 65 to 70% compared to conventional broadcast treatments. The RAATs system provides up to 85% control depending upon the rate of growth of the forage, the size of the grasshoppers and coverage obtained.
Two insecticides can be used with the RAATs application method: Dimilin® 2L, and Prevathon®. Dimilin®2L works by interfering with the molting process of grasshoppers and Prevathon® works by contact/ingestion. Both insecticides should be applied when most of the grasshopper population issecond orthird instar nymphs or when the grasshoppers average ¾-inch long.
For other grasshopper control product options, please contact your local UNL Extension Office. Before using any pesticide, please read and follow label instructions.
