June 12, 2009

Fig. 1 Potato leafhoppers are small (above), but in significant numbers can cause severe damage to alfalfa (below).

Potato leafhoppers have arrived and are starting to injure alfalfa in many areas.

These are tiny, yellowish-green, wedge-shaped insects. They often blow into our region from the southeast from late spring through mid summer. Leafhoppers turn alfalfa yellow and stunt growth, and they especially hurt new seedlings.

An early symptom of leafhopper damage is a triangular or V-shaped yellow or purple area at the tip of alfalfa leaves. This discoloration is caused by a toxin the leafhopper injects into the alfalfa plant as it sucks out plant juices. As feeding continues, the entire plant can turn yellow and growth may stop.

Scouting

Starting now, check fields for leafhoppers at least weekly, before symptoms appear. If you detect leafhoppers early and they are still present, apply an insecticide. You may need to spray several times, though, since leafhoppers can migrate from other fields and reinfect your sprayed field.

If your alfalfa already is yellow and stunted, don't spray. Instead, mow your alfalfa to remove poisoned plant tissue and stimulate new growth. Unmown plants may not grow much more all year, lowering yield and potentially leading to stand loss over winter. After mowing new seedlings, spray insecticide after regrowth begins to protect growth. But don't automatically spray established stands. Instead, closely scout new regrowth at least weekly for leafhoppers. If they reappear, then use insecticides before much damage occurs.

Insecticides and Further Information

More information, especially about threshold levels and insecticides to help you protect your alfalfa from potato leafhoppers, is available from these resources:

1. NebGuide G1136, Potato Leafhopper Management in Alfalfa
2. UNL Department of Entomology List of Insecticides for Potato Leafhopper
3. Local Extension offices

Bruce Anderson
Extension Forage Specialist