Publication E-38
March 1974
Purdue University
Cooperative Extension Service
Department of Entomology
The Alfalfa Weevil
C. Richard Edwards, Extension Entomologist, and M. Curtis Wilson, Research Entomologist*
Indiana Alfalfa Pest Management
In 1974 the Cooperative Extension Service will notify growers when to look at their fields and how to decide to spray.
This notification will be made by radio, newspaper and directly to county agents.
Timing of Sprays
Timing of sprays is the most critical factor in controlling the alfalfa weevil. It is based upon accumulated units of temperature. Weevil development increases with higher temperatures. Weevil peaks will vary over the State from year to year and from south to north depending upon the season. Thus, the economic threshold will change during the season and from year to year because of temperature, weevil infestation, and the amount of alfalfa growth.
Weevil Habits and Damage
Damage to alfalfa begins when growth starts in the spring and is caused primarily by the larval (or growing) stage of the weevil. Young larvae are tiny yellowish-green worms. Older larvae are green with a white stripe running down the back. They grow to about 1/4 inch long. All stages of larvae have curved bodies and shiny black heads.
The larvae feed first in the growing tips and developing buds, then shred the foliage, giving infested fields a greyish appearance.
This feeding may cause heavy loss of the first cutting.
After feeding for 3 or 4 weeks, each larva spins a net-like cocoon on the plant or in soil debris. From this cocoon later emerges the adult alfalfa weevil -- about 1/4 inch long and light brown in color with a darker brown stripe down the middle of its back.
Many larvae might be present when the first cutting of alfalfa is made. These larvae, along with the newly-emerging adults, continue to feed on both the stubble and new growth, thus retarding development of the second cutting. The adults become inactive during the summer until fall when they commence laying eggs.
Helpful Management Practices
1.	Apply management practices that will result in a dense, vigorous crop of alfalfa.
2.	Make the first cutting in the bud stage; delayed cutting allows more damage to take place. Besides, early-cut alfalfa has higher protein content and greater nutritive value.
3.	Cut the crop clean and close and remove it from the field as soon as possible. Lack of food and exposure to hot sunlight kill many of the remaining larvae.
* Prepared in cooperation with Roger T. Huber, former Purdue Entomologist.
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of
Agriculture Cooperating. H. G. Diesslin, Director, West Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30,
1914.  It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity
and access to its programs and facilities without regard to race, religion, color, sex or national origin.