Grasshoppers in Alfalfa

Crop Injury: Multiple species of grasshoppers (Melanoplus spp.) feed on alfalfa foliage including the twostriped, differential, redlegged, packard, and migratory grasshoppers. Grasshoppers move into alfalfa field margins from neighboring rangeland or uncultivated areas when food sources in those areas are depleted. Grasshopper feeding can be extremely destructive when large populations cause severe defoliation. Seed fields and newly established plantings are particularly susceptible to grasshopper injury. 

Pest Description: Grasshoppers are long and slender with jumping hind legs. Nymphs resemble adults but lack fully developed wings. Twostriped grasshopper adults have two dark stripes running along the back of dark green and yellow bodies. Differential grasshoppers are yellow to green with dark v-shaped markings on their legs. Redlegged grasshoppers are yellow green with red markings on their back legs. Packard grasshopper nymphs have tiny dark spots on tan or lime green bodies; adults have brown, tan, and yellow patterns of bright coloration. Migratory grasshoppers are shades of grayish-brown, red, and tan, often with reddish hind legs. 

Life Cycle: Eggs overwinter within egg cases in the soil. Nymphs emerge in late spring or early summer and begin feeding. Adults continue to feed on plant tissue and lay eggs in summer and fall. Grasshoppers typically have one generation per year. 

Scouting: Grasshoppers can be especially problematic during hot and dry years, as well as the  following year. Injury is often found at the field edge, where grasshoppers enter the field after another food source becomes unavailable. 

Management: The primary control strategy for grasshoppers is insecticide application to areas where these pests are gathered. This includes not only at alfalfa field margins, but also to adjacent areas to prevent grasshopper infestation of alfalfa fields. The use of insecticide dry baits can also be effective, and poses less risk to insect pollinators. Adult grasshoppers are more difficult to kill than nymphs. 

Prepared and reviewed by the Alfalfa Pest Management Working Group.