ALFALFA WEEVIL DEGREE DAYS
The alfalfa weevil normally completes one generation (life cycle) per year. In Oklahoma, the life cycle begins when adults that have spent the summer months in an inactive state called aestivation in wooded or weedy areas along field borders and creeks, return to alfalfa fields in late October to begin feeding and laying eggs. Eggs are deposited within the hollow stems of alfalfa in groups of 5-25, and will remain there until hatching begins. Because egg laying continues through the winter, and it takes from 2-4 months in the low temperature before hatching begins, large numbers of eggs may build-up in fields during January and February. Egg hatch and the appearance of damaging populations of weevil larvae is greatly dependent upon weather conditions.    Warmer temperatures during winter will result in hatching of larvae and damage by early March. Colder temperatures and hard freezes (0-10 degrees F) will result in many eggs being killed and slower hatching with damage often delayed until April. The "shake bucket" scouting method is based on a record of temperatures (heat energy) that occur during winter and spring using degree days (DD). The accumulation of heat energy (DD) for development of weevil eggs is calculated for each day, then totaled for the year, beginning on January 1. In over 25 years of field observations, damaging populations of weevil larvae have never occurred before DD from January 1 have exceeded 150 (normally about March 1).    Summary:   It is recommended that field scouting for weevil larvae not begin until 150 DD have accumulated. Additional information on the life cycle and control of the alfalfa weevil can be found in OSU Extension Facts No. 2097 and OSU Extension Facts No. 7150.
Richard Berberet, Alfalfa Entomologist  Department of Entomology and Plant Pathology  Oklahoma State -University

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