Alfalfa Agronomic Topics
Alfalfa Weevil
Dave Schwartz, GCS Agronomist, June 2009
Alfalfa weevil damage is being reported in alfalfa fields in central Minnesota. Larvae, up to 5/16 inch long when mature, feed on leaf tissue and tend to concentrate on buds and newly emerging leaves. Early feeding injury of immature larvae appears 
as pinholes in leaves. As larvae mature, they remove leaf tissue between leaf veins giving the leaf a skeleton appearance. Fields with high weevil populations may take on a silver appearance as the green tissue between veins of leaves is removed. Larvae feeding (3 to 4 weeks) normally takes place from late May to mid June.
Alfalfa weevil larvae are light green colored, 3/8 to 5/16 inch long when mature; have a black head, and white line down the center of the back. They blend in very well with plant tissue so may be difficult to locate. They resemble clover weevils in appearance except clover weevils are much larger and have a tan head.
The economic threshold for alfalfa weevil larvae following first cutting is eight or more larvae per square foot.
(Photos Courtesy of the University of Illinois)
