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Alfalfa Weevil Will Be the First Insect We'll Watch For

March 16, 2001
As usual, the alfalfa weevil will receive considerable attention in the early issues of the Bulletin because it's the first insect pest of field crops in Illinois to become active each spring. As indicated in the article "Will Another Mild Winter Promote Insect Problems?", alfalfa weevils overwinter as eggs in southern Illinois. When spring temperatures consistently exceed 48°F, larvae hatch from the eggs and crawl to the terminal leaves, where they feed and develop.

Two distinct peaks of larval activity usually occur in southern Illinois, one from fall-deposited eggs and one from spring-deposited eggs. Hatching of overwintering eggs usually occurs when 200 degree-days (above a base temperature of 48°F) accumulate beyond January 1, and we suggest that scouting should begin when 250 to 300 degree-days accumulate. An early peak of third-stage larvae from overwintering eggs occurs after an accumulation of 325 degree-days; a second major peak of third-stage larvae from spring-deposited eggs occurs after an accumulation of 575 degree-days.

At the time this article was prepared, accumulated degree-days were not available from the Illinois Climate Network run by the Illinois State Water Survey. We will provide actual and projected accumulated degree-days in issue no. 2 of the Bulletin, which will be published during the first week in April. In the meantime, we encourage people in southern counties to begin watching for alfalfa weevils and signs of their feeding injury, especially if temperatures consistently exceed 48°F. At this time last year, some folks had already observed evidence of injury caused by alfalfa weevils. During most years, alfalfa weevil activity in southern Illinois begins in mid- to late March or early April.

At a forthcoming meeting of entomologists at the end of March, we will learn more about the status of alfalfa weevils in the north-central states. We'll report what we learn in a future issue of the Bulletin.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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