Continuing Investigations into the Relationships among Leafhoppers, Glandular-haired Alfalfa, and Timing of Insecticide Application

The potato leafhopper (PLH) is the most serious insect pest of alfalfa in Wisconsin and the Upper Midwest. PLH injury to alfalfa can result in leaf yellowing (“hopperburn”), plant stunting, loss of yield and forage quality, and reduced alfalfa stand persistence. Leafhopper populations are a perennial problem in new alfalfa seedings, and they frequently increase to damaging levels on the second and subsequent crops in established alfalfa stands. Until recently, crop scouting and insecticide application when warranted was the only effective means of PLH management. However, development and eventual release of glandular haired (GH) alfalfa varieties in 1997 may be changing the way we manage this pest and may ultimately alter its pest status in alfalfa. On the other hand, leafhopper resistance exhibited by the GH varieties has so far proved to be less than complete, and thus scouting is still necessary for effective PLH management.