Starting with the first warm spring days they migrate to alfalfa fields and lay eggs in new or dead plant stems. Peak egg lay and larval feeding is usually around early and late May, respectively. Larvae spin a white silken cocoon when development is complete and adults emerge within two weeks. Adult weevils are not active during the summer months but occasionally will be collected in sweep nets. Begin scouting activity at egg hatch.
Some larvae cause damage by chewing tiny holes in the upper leaves.
As larvae grow, the amount of foliage consumed increases dramatically. When larval numbers are high, complete defoliation of the upper leaves can occur. Peak damage often occurs when the first cutting is ready for harvest. Feeding is usually completed by the time second crop regrowth is 8-10 inches tall. Scouting and Economic Threshold Start monitoring alfalfa at 300 degree days.