The alfalfa weevil overwinters in both adult and egg stages. Egg laying occurs in fall and spring, the larvae that hatch from spring laid eggs cause the most crop damage. Eggs are laid in the alfalfa stem when temperatures are above 48oF. They may begin hatching in early March where temperatures are warm.
Adult alfalfa weevils (Hypera postica) are brown in color with a dark triangular marking on their back. The weevils tend to be about 3/16 of an inch long. Females lay bright yellow eggs on the inside of the stem of the infested plant. Most eggs are laid in the spring when the weevil returns to the crop. Weevil larvae will eat small holes in leaves beginning in April or May and they will shed their skin three times before reaching their maximum size. The adult weevil overwinters in protected spots such as wooded areas, windbreaks, and other protective habitats.
Because levels of the alfalfa weevil do not reach recommended treatment levels, it is important to scout for the weevil before making any control treatment efforts. The only recommended organic control is Spinosad. This should be applied to the plants while the pest is in the larval stage.