Publication E-38
December, 1968
Purdue University
Cooperative Extension Service
Department of Entomology
The Alfalfa Weevil
ITS 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 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 complete loss of the first cutting.
After feeding for 3 or 4 weeks, each larva spins a net-like cocoon on the plants 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 may 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. Most of them leave alfalfa fields but return again in October to spend the winter.
In counties along the Ohio River, 1/3 or more of the eggs are usually laid in late fall or early winter and hatch in late winter or very early spring. Farther north in the State, most of the eggs will probably be laid in green alfalfa stems in the spring.
CONTROL
Alfalfa weevil control is time-consuming and costly. Only those chemicals that do not leave unlawful residues on the crop can be used. Farmers who expect to continue to grow good alfalfa will need to adjust their cultural practices and initiate a spray program. Here are the 1969 alfalfa weevil control measures suggested for Indiana:
Crop Management
1.	Apply those management practices that will result in production of a dense, vigorous crop.
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 sun kill many of the remaining larvae.
Chemical Control
Insecticides for alfalfa weevil control are listed in Table 1. South of U. S. 36, 2 or 3
Adult alfalfa weevil
12/68
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. G. Diesslin, Director, Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30, 1914.