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Curt Laub, Research Associate, Rod Youngman, Extension Specialist, and Theresa Dellinger, Graduate Student
Potato leafhopper populations are over threshold levels in Campbell, Montgomery, and Orange Counties. These areas represent a large portion of the alfalfa growing region of the state, so this is to alert all alfalfa growers to scout for potato leafhopper in the next few weeks. Particular attention should be paid to fields that were recently cut and have less than 14 inches of growth.
Potato leafhopper populations ranged from 0.7 per sweep in Campbell County to 3.7 per sweep in Orange County. The action threshold changes depending on stem length, so taller alfalfa can withstand higher numbers of potato leafhoppers. In Campbell and Montgomery Counties, most of the potato leafhoppers counted were adults, which tells us that high numbers of eggs are being deposited. These eggs will be hatching in the next few weeks and we expect very high numbers of nymphs to start feeding. In Orange County about half the leafhoppers were nymphs, indicating that eggs have been hatching there for about a week.
Potato leafhopper damage to alfalfa may be severe, especially to fields that are just now being harvested. Fortunately, ample soil moisture this spring has resulted in excellent alfalfa growth. However, soils are starting to dry up, placing additional stress on alfalfa plants.
Growers are advised to monitor all alfalfa fields for potato leafhopper, especially those fields that have recently been cut. Procedures for monitoring potato leafhopper and recommended insecticides for controlling this insect are described on pages 128-130 of the 2001 Virginia Pest Management Guide for Field Crops-Extension Publication no. 456-016 (or go to http://www.ext.vt.edu/pubs/pmg/fc4a.pdf to download a PDF file of the Field Crops Insects section from the Pest Management Guide-then scroll down to page 128).
Remember, any alfalfa that is taller than 14 inches and has leafhopper levels exceeding the threshold should be harvested early rather than sprayed.
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