Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


Alfalfa Weevil Update



Development of alfalfa weevil is based on climatic temperature. Alfalfa weevils develop whenever the temperature is above 48 degrees. Therefore, the stage of development is estimated based on Growing Degree Days (GDD) Base 48. The formula for a given day is the daily high (minimum 48) plus the daily low (minimum 48) divided by 2 to determine the average temperature for the day. From the average temperature for the day, subtract 48. If the result is a positive number, add it to the GDD of all prior days with a positive result.

Alfalfa weevils begin to hatch at 300 GDD base 48 and quit feeding at 900 GDD Base 48. Because south facing slopes are somewhat warmer than average, they should be scouted beginning at 200 (south of I-80) - 250 (north of I-80) GGD Base 48.

A map from the mesonet base 48 is available at

For details on managing this insect, see the April 14, 2015 ICM News article, April 11, 2014 ICM News article, which has updated thresholds, April 2, 2012 ICM News article, the April 8, 2011 ICM News article, pages 87 - 89 of the April 17, 2006 Integrated Crop Management Newsletter, and/or pages 48 - 49 of the April 11, 2005 Integrated Crop Management Newsletter.

If harvesting is used to manage alfalfa weevils, check re-growth in 4 - 5 days using the strategies listed on pages 2 - 3 of the June 13, 2005 Integrated Crop Management Newsletter.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 5, 2014, except the data in the table was last updated the day after the most recent data listed.
Contact: Virgil Schmitt

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