Degree-day information indicates that alfalfa weevil larvae should have started hatching in southern Iowa on March 30-31. In central Iowa counties, weevils should be hatching by the middle of April, and in southern Iowa, weevils should hatch the last full week of April. Proper management of this insect requires timely scouting, correct identification, determination of population levels, and if necessary, cutting the hay or spraying an insecticide. Alfalfa weevil larvae can be very destructive to first-cutting alfalfa, so fields should be scouted. Larvae remove leaf tissue, beginning with the new leaves at the top of the plant, then work down the stem to other leaves. This feeding reduces forage quality and quantity.
Iowa State University
Rice, Marlin E. and Pope, Richard O., "Alfalfa weevil predictions for Iowa, 2007" (2007). Integrated Crop Management News. 1103.
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