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Alfalfa WeevilsAdult alfalfa weevils are brown in color with a dark triangular marking on their back. The weevils tend to be about 3/16 of an inch long. Bright yellow eggs are laid by the female on the inside of the stem of the infested plant. Some eggs are laid in the fall, but most are laid in the spring when the weevil returns to the crop. These eggs do not hatch simultaneously, thus larvae vary in size. Larvae will shed their skin three times before reaching their maximum size. At this point they tend to be 3/8 of an inch long and are green with a white strip down their back. The cocoons are found once larvae cease feeding and drop to the soil. The appearance of the cocoon is that of a small, white colored ball made from woven silk and dried alfalfa leaf pieces.
Signs of weevil damage can first be spotted in April and May when larvae eat small holes in upper leaves and buds causing the leaves to become white or gray. The adult weevil overwinters in protected spots such as wooded areas, windbreaks, and other protective habitats.
In the late 1950's the United States Department of Agriculture began introducing several species of parasitoids from Europe (the native range of the alfalfa weevil). These parasitoids, along with a naturally occurring fungus, are well established and now naturally keep the alfalfa weevil under biological control in the northeastern U. S., California, Colorado, and Oklahoma. Because they occur naturally, they are not available for sale. However, in the southeastern United States the Alfalfa Weevil is still a problem. If you live in the South East, check out our biological controls below.
Photo Courtesy of: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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