CSU Coop Extension Pest Alert Bulletin - Vol. Alfalfa should be scouted now for alfalfa weevil. Reports from southeast and western Colorado indicate that a significant infestation is underway. Damage starts as small holes in new leaflets and progresses to heavy skeletonizing of the terminals.
Losses vary with the intensity of the infestation, growth stage and condition of the crop.
Alfalfa weevil larvae are green or yellow in color, with a black head and a white stripe down the back. These should not be confused with the cloverleaf weevil, which is similar in appearance but has much less damage potential. Alfalfa weevil management currently relies on either early harvest or on insecticide treatments based on one of several action thresholds. If the crop has reached the bud stage consider cutting early. Large infestations may not be controlled completely unless the crop is green-chopped.