The more advanced generations of alfalfa (Medicago sativa L.) cultivars and experimentals resistant to potato leafhopper (PLH), Empoasca fabae (Harris), were released in 1998 and planted at Ithaca that year. Cultivars released in 1999 were planted in a separate trial in spring of 1999. The trial design is a split-plot with the main plots as insecticide treatment vs. no treatment. In 2000, PLH populations were above threshold in both trials on 26 July, 10 days prior to harvest 2; however, insect populations were below threshold at second harvest. In the trial planted in 1999, first harvest yield data indicated a carryover effect showing that plots which had received spray treatment in 1999, and thus much less PLH damage, were higher yielding in 2000, relative to plots unsprayed in 1999. Similarly, the 1999-unsprayed resistant entries yielded more in 2000 than 1999-unsprayed susceptible entries, again likely because of PLH damage in the seeding year carrying over and affecting the susceptible entries in 2000. At second and third harvests of this trial, however, the resistant entries yielded less than the susceptible ones.