Publication E-38
January 1971
Purdue University
Cooperative Extension Service
Department of Entomology
The Alfalfa 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 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.
late winter or very early spring. Farther north in the State, most of the eggs are laid in green alfalfa stems in the spring.
HELPFUL MANAGEMENT PRACTICES
1.	Apply management practices that will result in production of 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.
Adult alfalfa weevil
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. Most of them leave alfalfa fields but return again in October to spend the winter.
In counties along the Ohio River, one third or more of the eggs are usually laid in late fall or early winter and hatch in
Control regions.
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.
INTEGRATED APPROACH TO CONTROL
Parasitic insects help to control the alfalfa weevil. The management practices and spray programs suggested in this publication are designed to encourage plant growth and provide protection to these natural enemies. Insecticides are listed in Table 1. Timing and number of sprays are expected to vary according to location. See map for control regions.
Region 1: One application probably sufficient. Apply when 50% of the tips show feeding. Avoid stubble sprays to protect tiny wasp parasites that have reduced infestations in this area.