Comparison of potato leafhopper-resistant and susceptible alfalfa in New York

Potato leafhopper [PLH; Empoasca fabae (Harris)] is the most damaging pest of alfalfa (Medicago sativa L.) in midwestern and eastern states. Our objective was to compare alfalfa populations with glandular-hairs (PLH-resistant) and susceptible populations for forage yield and quality, PLH damage, and PLH nymph and adult populations. Potato leafhopper-resistant and susceptible alfalfa populations were planted in New York (NY) plot trials in 1997, 1998, and 1999, and compared seeding year through second production year. When PLH populations exceeded the action threshold for NY, PLH-resistant populations had lower PLH damage scores (2.3 vs. 3.7), fewer number of nymphs per 10 stems (3.5 vs. 6.2), and fewer adult PLHs per five sweeps (9.1 vs. 18.1) than susceptible populations. However, PLH-resistant populations yielded more than susceptible populations only in one of four trials. Irrespective of PLH damage level, PLH-resistant populations had higher crude protein (CP) concentration (203 vs. 194 g kg^-1) and matured earlier than susceptible populations. Seeding year trials were severely damaged by PLH. The following year at first harvest, PLH-resistant populations yielded more than susceptible populations (0.24 Mg ha^-1 more in 1997 trial, and 0.61 Mg ha^-1 more in 1999 trial), even though PLHs were not causing economic damage. Resistant populations that were not treated with insecticide averaged lower total season yields than insecticide-treated, PLH-susceptible populations (0.29 Mg ha^-1 less in seeding year, 0.95 Mg ha^-1 less in production yrs). Potato leafhopper-resistant populations provide benefits to growers such as higher CP concentration and less hopperburn, but do not provide complete protection against yield loss from PLH damage.