REDUCED EMPOASCA-FABAE (HOMOPTERA, CICADELLIDAE) DENSITY IN OAT ALFALFA INTERCROP SYSTEMS

Potato leafhopper, Empoasca fabae (Harris), is a major pest of spring-planted alfalfa (Medicago sativa L.). In two experiments, an alfalfa monoculture and an intercrop (mixture of alfalfa and oat, Avena sativa L.) were evaluated for their potential for reducing leafhopper densities. The 1988 experiment tested the effects of the intercrop and leafhopper control, whereas the 1989 experiment tested the effects of weed control and two oat cultivars differing in stature. Leafhopper density (number per square meter and number per 100 alfalfa stems) and various plant parameters were measured in both experiments. Adult leafhopper densities per square meter were reduced an average of 82.6% in 1988 and 77.3% in 1989, and densities per 100 stems were reduced an average of 64.7% in 1988 and 54.5% in 1989, in the intercrop compared with the alfalfa monoculture. Nymph densities per square meter were reduced an average of 85.5% in 1988 and 89.5% in 1989, and densities per 100 stems were reduced an average of 74.8% in 1988 and 82.7% in 1989, in the intercrop compared with the alfalfa monoculture. The intercrop was characterized as having reduced alfalfa biomass, reduced alfalfa stem density, reduced alfalfa maturity (1989 only), increased alfalfa stem length (1989 only), reduced weed biomass, and increased shading of alfalfa in comparison with alfalfa monoculture. Thus, factors that may cause the observed reduction in leafhopper density may be associated with the host plant or the habitat condition. The study corroborates other studies that have shown reduced potato leafhopper densities in grass-legume mixtures, and suggests that an oat-alfalfa intercrop may reduce the need for responsive tactics for leafhopper management on spring-planted alfalfa compared with the need in alfalfa monoculture.