Issue No. 3, Article 5/April 14, 2006
Anticipating Alfalfa Weevils
For a long time now, we and entomologists throughout North America have been using degree-day accumulations to keep track of alfalfa weevil development and predict occurrences in their life cycle. In the Bulletin last week (issue no. 2, April 7, 2006), Kelly Cook provided a table showing the relationship between accumulated degree-days and alfalfa weevil development. She also encouraged readers to visit the Degree-Day Calculator. I echo her encouragement.
The calculator enables anyone to obtain current and predictive information about alfalfa weevil development in any area of Illinois. Click on Degree-Day Calculator in the upper left corner, then choose between the calculator and maps to obtain different types of information. For example, we no longer publish maps of degree-day accumulations in the Bulletin because more timely maps can be obtained at the Web site. On the date that I wrote this article (April 12, 2006), the degree-day accumulations through April 11 revealed that 300 degree-days (base 48°F) had accumulated anywhere south of a line from St. Louis (west) to Carmi in White County (west). However, by the time you read this, the map will have been updated, so you can obtain more recent information. The maps for 1-week and 2-week projections also are updated as 2006 temperatures are included with historical temperature data. Obviously, if temperatures are warmer than "average," alfalfa weevil development will accelerate, and the 1-week and 2-week projections will change accordingly.
If you prefer to obtain information for specific regions of Illinois, you can use the Degree-Day Calculator to determine actual degree-day accumulation and 1-week and 2-week projected totals for 18 different locations (indicated on the map). This information is adjusted regularly as current weather data are added.
Thus far, reports of significant alfalfa weevil activity have been few and far between. Most people have found only small instars, with evidence of their feeding identified as pinholes in the leaves. We encourage continued scouting, with tips as outlined in Kelly Cook's article. Warmer weather will speed things up considerably.--Kevin Steffey