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. Howeve r, development and eventual release of glandular haired (GH) alfalfa varieties in 1997 is changing the way we manage this pest and may ultimately alter its pest status in alfalfa. On the other hand, the success of GH varieties for stand-alone PLH control has thus far been inconsistent, and therefore scouting is still necessary for effective PLH management.

The purpose of this study was to investigate the extent to which treatment thresholds currently recommended in Wisconsin for PLH management in alfalfa may need to be adjusted for glandular haired alfalfa cultivars with resistance to PLH. A further aim of this study was to assess the effectiveness of resistance of GH alfalfa to the potato leafhopper and to look at the implications for using GH alfalfa in PLH control.