Glandular-haired cultivars reduce potato leafhopper damage in alfalfa

Glandular-haired alfalfa (Medicago sativa L.) cultivars developed for resistance to potato leafhopper [Empoasca fabae Harris] (PLH) have not been evaluated across a wide geographic area. Our objective was to evaluate forage growth, yield, insect damage, and stand density of glandular-haired and standard alfalfa cultivars with and without insecticide control of naturally occurring PLH infestations across the Midwest USA. Nine glandular-haired and five standard cultivars were evaluated from 1996 to 1998 in field experiments in Ohio, Indiana, Wisconsin, and Minnesota. Scheduled insecticide applications increased total yield of all cultivars, the response declining with increasing latitude (yield advantage = 32.7 - 0.72 × latitude; r² = 0.86, P = 0.05). Depending on location, total yield loss due to PLH damage ranged from 5 to 23% for the standard cultivars and 1 to 10% for the glandular-haired, commercially released cultivars (GR). Yield loss from PLH feeding in the GR cultivars was less than half of that observed in standard cultivars in environments where PLH stress was high. The GR cultivars yielded 1.1 Mg ha^-1 more per year on average than the standard cultivars without insecticide under high PLH stress in Ohio and Indiana. Potato leafhopper nymph densities were lower in glandular-haired cultivars than in standard cultivars. Cultivars had similar yield when treated with insecticide or when PLH populations were low. Glandular-haired alfalfa cultivars were not immune to PLH damage; however, they can substantially reduce yield losses caused by this pest and provide a useful new tool for integrated pest management strategies.