HPIPM:Grasshoppers Sorghum
Authors: John B. Campbell & Frank B. Peairs[1]
Identification (and life cycle/seasonal history)
There are many different species of grasshoppers, with some having a greater pest potential than others. Correctly identifying a species is important because (1) species vary in their biotic potential and in their capacity for causing damage; (2) depending on their food habits, species may be either pests or beneficials; (3) certain species of pest grasshoppers are highly migratory and often pose a serious threat to distant crops; (4) species vary in their seasonal cycle (period of hatching, development, and reproduction) which in turn affects the timing of control treatments; (5) because current chemical and biological methods of controlling grasshoppers are more sophisticated, their effective use requires greater knowledge of the pests' life histories and habits; (6) as environmental impacts of control are more finely evaluated, identification of species is important in the selection of management strategies. Common pest species include: clearwinged grasshopper, Camnula pellucida; differential grasshopper, Melanoplus differentialis; migratory grasshopper, Melanoplus sanguinipes; twostriped grasshopper, Melanoplus bivitattus; and redlegged grasshopper, Melanoplus femurrubrum.
Most grasshoppers overwinter as eggs in the form of a pod laid in the soil. These elongate-shaped pods may contain from 20 to 120 eggs each. Eggs hatch into nymphs in late May and June, maturing in two to three months. By August most nymphs have matured to the adult stage. Grasshoppers feed during the day and rest during the afternoon and night on vegetation.
The following website provides a comprehensive source of information on grasshopper biology, ecology, identification and management of grasshoppers and crickets in North America. [2]
Plant Response and Damage
Grasshoppers can be a pest to many crops. There are many species of grasshoppers, but only a few actually have pest potential. Populations may vary greatly from year to year and season to season. Often grasshopper populations develop in uncultivated areas and move into cultivated fields. Mostly grasshoppers feed on leaves.
Monitoring
Hazard Maps are developed each year as a cooperative effort of USDA-APHIS-PPQ and are available at the following site. http://www.sidney.ars.usda.gov/grasshopper/http://www.sidney.ars.usda.gov/grasshopper/
Management
Table 1. Treatment thresholds for immature and adult grasshoppers (from University Minnesota)
| Rating | Immatures/yd2 | Adults/yd2 | ||
|---|---|---|---|---|
| Margin | Field | Margin | Field | |
| Light | 25-35 | 15-25 | 10-20 | 3-7 |
| Threatening | 50-75 | 30-45 | 21-40 | 8-14 |
| Severe | 100-150 | 60-90 | 41-80 | 15-28 |
| Very Severe | 200+ | 120+ | 80+ | 29+ |
Chemical Control
Treat crop borders when immatures are small and numbers are moderate. Timing of grasshopper control depends on the potential for crop loss, crop value, size (stage) of grasshoppers present. Grasshopper control is most effective before the insects become large nymphs or adults, as these stages are more mobile and more difficult to control.
Chemical control may be justified when adult grasshopper populations are threatening, according to the population densities shown in Table 1. Re-infestation originating from outside the field may occur after 10 to14 days. Use the higher dosages for adults, lower for the more immature. Sufficient gallonage is important. Products for control of grasshoppers in noncrop areas adjacent to sorghum fields include acephate2 and Dimilin 2L. See A Guide to Grasshopper Control in Cropland in this guide for more information.
Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.
