Grasshoppers and Mormon crickets are two of the most economically significant pests affecting forage production on rangelands in Eastern Oregon. It is estimated that they consume greater than 20% of available forage on rangelands annually. Additionally, large outbreaks tend to correspond with drought years, further increasing the losses due to the already limited forage available for livestock.
Determining when to treat
With any pest management decision, the costs and benefits associated with treatments must be considered. The economic threshold for grasshopper and Mormon cricket control ranges between 8–24 grasshoppers per square yard. Densities greater than 24 per square yard indicate that treatment will be beneficial in nearly all situations, while densities between 8–24 per square yard will depend on overall forage availability and the actual cost of treatment.
Field-based surveys are the only way to determine if the grasshopper and/or Mormon cricket population exceeds the economic threshold. Information regarding surveying can be found from the Oregon Department of Agriculture and the Oregon IPM Center.
Incorporating the economic threshold when deciding to manage grasshoppers is necessary as treatment can be quite costly, especially on large parcels of rangelands common throughout Eastern Oregon. Often the cost of application exceeds $15 per acre, not including the cost of chemical. Since grasshoppers are highly mobile, treating a single field may only provide temporary relief if adjacent properties are not treated, as the insects often simply move from untreated areas. Treatments are most effective when applied to large areas, incorporating as many adjacent land owners as possible.
Pesticide options
There are a number of chemical control and application options suitable for rangeland or pasture application when treating for grasshoppers and/or Mormon crickets. The best option will depend on a number of factors, including:
- Forage species
- Irrigated versus dryland
- Grasshopper and/or Mormon cricket stage of development
- The presence of beneficial insects.
The table in the Pacific Northwest Insect Management Handbook for rangeland grasshoppers and rangeland Mormon crickets is intended to provide information about active ingredients commonly used to manage grasshoppers and Mormon crickets in Oregon. Columns provide information regarding the capacity for residual control, impact on non-target insects (selective pesticides), and if the active ingredient controls grasshoppers, Mormon crickets or both. With any pesticide application and always follow the instructions for application on the label. Consult your local Extension office or crop consultant for site specific considerations and for printed handouts.
An additional consideration is if the product label includes Reduced Agent and Area Treatments (RAATs). A RAATs application involves applying treatments in rows, leaving a gap of untreated ground between. RAATs has been shown to be 80-95% effective compared to standard blanket treatments, while reducing the amount of active ingredient by 60-75% and reducing total application cost by upwards of 50%. More information is available from the University of Wyoming.
Use pesticides safely!
Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.
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