Forage quality of potato leafhopper resistant and susceptible alfalfa cultivars

Glandular-haired alfalfa (Medicago sativa L.) cultivars resistant to potato leafhopper [Empoasca fabae Harris] (PLH) have not been evaluated for forage quality across a wide region. Our objective was to compare forage quality of PLH resistant and susceptible alfalfa cultivars with and without insecticide control of PLH across the Midwest USA. Six commercially released PLH resistant and five susceptible cultivars were evaluated from 1996 to 1997 in field experiments in Ohio, Indiana, Wisconsin, and Minnesota. The resistant cultivar group was more mature at harvest but equal to or higher (P ≤ 0.05) in crude protein (CP) concentration than the susceptible group regardless of insecticide treatment Averaged over all harvests, the CP advantage for the resistant group was 11 to 13 g kg^-1 for insecticide treated and untreated controls, respectively. Without insecticide, the resistant group was equal to or lower (P ≤ 0.05) in neutral detergent fiber (NDF) and equal to or higher (P ≤ 0.05) in in vitro digestible dry matter (IVDDM) than the susceptible group, except at harvests when PLH severely stunted the susceptible cultivars, which likely increased leaf/ stem ratio. With insecticide, the resistant group was lower in NDF by 15 to 25 g kg^-1 and higher in IVDDM by 19 g kg^-1 than the susceptible group. Potato leafhopper feeding had less effect on forage quality and maturity of PLH resistant cultivars than susceptible cultivars. The PLH resistant cultivars we evaluated generally had higher forage quality than susceptible cultivars when grown with or without insecticide application despite being more mature at harvest.