Potato Leafhopper Management: Effects on Production and Quality of Alfalfa-Timothy Mixtures

Alfalfa (Medicago sativa L.) mixtures with grasses, especially timothy (Phleum pratense L.), are widely planted in the Great Lakes Region, but most information on potato leafhopper [Empoasca fabae (Harris)] (PLH) management for new stands based on alf alfa monocultures. Field research was conducted in 1991 and 1992 to evaluate the ability of alfalfa to recover from PLH injury following insecticide application and to compare the effect of injury on yield and quality of first-year monocultures or mixtures. Four replicates of alfalfa monoculture and alfalfa-timothy mixtures were established each year. One week after the first harvest in early July, eight split-plot treatments were established in each main plot: an uncaged check, a caged check, and six combinations of two PLH infestation densities (25 or 50 PLH adults m⁻²) and three insecticide application dates (1 wk after infesting plots, 3 wk after infesting plots, and unsprayed). Crop mixture had no effect on PLH nymphal populations on a per stem basis. Although differences between years were noted, delaying insecticide application generally reduced forage yield and quality, delayed crop maturity, and increased weed content, particularly in forage mixtures. There was little evidence that seedling timothy could compensate for PLH injury to alfalfa. Data on stem elongation and dry matter accumulation indicated that alfalfa can recover from leafhopper injury; however, dry matter production did not increase for at least 2 to 3 wk following a spray application. Reductions in forage crude protein due to PLH injury were a result of both reduced crude protein content in the alfalfa and an increase in the proportion of weed biomass in the forage. Early detection and rapid response to economically significant populations are necessary to realize the greatest benefit from treatment. The presence of timothy in the mixture does not alter PLH management recommendations for new stands. Research supported by the Coop. State Res. Serv., USDA, under Subcontract no. USDA-TPSU-CU-3361-686 from The Pennsylvania State Univ. and Hatch Project 401.