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Field Notes: Potato Leafhoppers in alfalfa

Valerie Tate

Potato leafhoppers migrate to Missouri during spring storms and are found in alfalfa fields in summer months. They feed on alfalfa leaves causing losses in both yield and forage quality. First-year stands are the most susceptible to damage. Established stands can tolerate more insect pressure.

Adult potato leafhoppers are small, lime green, triangular-shaped insects about 1/8 of an inch long with a broad head, large white eyes and clear wings. Immature potato leafhoppers do not have wings, are yellow to pale green in color and are smaller than adults. When they feed on an alfalfa leaf, they pierce the leaf to feed on the plant sap. This leaves a yellow V shaped mark on the tip of the leaf often called “hopper burn”. Injured plants will be stunted and the leaves will fall off resulting in lower yield and reduced hay quality.

Adult leafhoppers will fly away and nymphs move to the underside of plant leaves when disturbed. Therefore, the best way to determine if there are enough insects present to cause economic damage is to use a 15-inch sweep net. Move to an area of the field which has not been disturbed. Take 20 pendulum sweeps three to four inches into the plant canopy in five locations in the field. Count the number of potato leafhoppers collected. An economic threshold table developed at Penn State is available to determine when insecticides should be applied. It takes into account the number of leafhoppers present, alfalfa height, the value of the hay and the cost of the insecticide. Contact your local

MU Extension Agronomist for more information. For more information contact Valerie Tate, field specialist in agronomy for University of Missouri Extension by email at tatev@missouri.edu or call at 660-895-5123. MU Extension programs are open to all.