Issue No. 3, Article 2/April 10, 2009
Alfalfa Weevil Hatch Underway in Southern Illinois
A quick review of degree-day accumulations (base 48 °F) from January 1 through April 7 indicates that alfalfa weevils are hatching from eggs across the southern third of Illinois. This spring event occurs each year when 300 (base 48 °F) degree days have accumulated from January 1. Degree-day totals for a number of locations through April 7 are as follows: Belleville, 278; Carbondale, 335; Dixon Springs, 324; Fairfield, 282. First and second instars are very likely already causing some light leaf-feeding injury, especially on slopes warmed by the sun.
I encourage readers to visit the degree-day calculator website to keep track of alfalfa weevil development throughout the spring. This site also should be helpful to track the development of many other insect pests of field crops. Life cycle information and scouting protocols have been thoroughly described for alfalfa weevils and can be viewed here. If you are observing significant alfalfa weevil activity, please share your observations with us.--Mike Gray