Publication E-38 November, 1966
Purdue University
Cooperative Extension Service
Department of Entomology
The Alfalfa Weevil
The alfalfa weevil is rapidly becoming a very serious pest of alfalfa in Indiana. First reported in the state in 1964, it is now expected to cause extensive damage to alfalfa in the southern half of Indiana during 1967.
By 1968 it will probably be firmly established throughout the entire state.
ITS HABITS AND DAMAGE
Damage to alfalfa begins shortly after growth starts in the spring, and is caused primarily by the larval (or growing) stage of the weevil. The larva is a small, curved, green worm with a black head and white stripe running down its back. Fully-grown, it is about 1/4 inch long. It feeds first in the growing tips and developing buds, then shreds the foliage, giving an infested field 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.
winter or very early spring. Both adults and newly-hatched larvae may be found in the crowns of alfalfa plants in late winter. Further north in the state, habits of the weevil should be somewhat different, and most of the eggs will probably be laid in green alfalfa stems in the spring.
Adult alfalfa weevil
ALFALFA WEEVIL CONTROL
Control of the alfalfa weevil is time-consuming and costly. This is largely because of restrictions placed on the use of insecticides. 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 make some adjustment in their cultural practices and initiate a spray program. Here are the alfalfa weevil control measures currently suggested for Indiana:
Many larvae are present when the first cutting of alfalfa is made. These larvae along with the newly-emerging adults continue to feed on both cut stubble and new growth, thus retarding development of the second cutting. Later cuttings are not injured. The adults become inactive during the summer and spend the winter in and around alfalfa fields.
In counties along the Ohio River, it appears that most of the eggs are laid in late fall or early winter and hatch either in late
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.