June 27, 2008

Potato leafhoppers have arrived and are starting to injure alfalfa in many areas. These tiny, yellowish-green, wedge-shaped insects often blow into our region from the southeast in early to mid-summer.

Figure 1. Adult and nymph potato leafhopper.

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.

Starting now, check fields at least weekly for leafhoppers before symptoms appear. If you detect leafhoppers early and they are still present, insecticides can kill them easily. 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, do not spray. Instead, first mow your alfalfa to remove poisoned plant tissue and to stimulate new growth. Unmown plants might not grow any more all year, lowering yield and potentially leading to stand loss over winter. After mowing new seedlings, spray insecticide after regrowth begins to improve growth, but don't automatically spray established stands. Instead, closely scout new regrowth at least weekly for leafhoppers. If they reappear, use insecticides before much damage occurs.

More information, including treatment thresholds, is available in the June 15, 2007 CropWatch story, Managing Potato Leafhoppers in Alfalfa.

local extension offices.

Bruce Anderson
Extension Forage Specialist