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Alfalfa Weevil Report

May 10, 2002
I've said about all I need to say about alfalfa weevils by now. People in southern and central Illinois have experienced some of the heaviest infestations of alfalfa weevils they have witnessed in many years. The defoliation caused by the larvae has been excessive. Wet weather has hampered control with insecticides and, in some instances, reduced the efficacy of an insecticide after it had been applied.

Figure 4 and Figure 5 show actual and projected degree-day accumulations (base 48 deg F), respectively, from January. Figure 4 indicates that alfalfa weevil larvae are active throughout the state. By May 20 (Figure 5), and even before in southern Illinois, alfalfa producers will have lived through the onslaught, except in northern counties.

In last week's Bulletin (issue no. 6, May 3, 2002), I mentioned that harvesting alfalfa early is an alternative to applying insecticides. However, the wet ground has delayed harvest in many counties. As the alfalfa continues to grow, the plants will produce more blossoms. Consequently, I urge anyone who still intends to apply an insecticide for control of alfalfa weevils to be aware of the effect of insecticides on honey bees visiting alfalfa fields. Spraying blossoming alfalfa can be extremely hazardous to bees. Coordinate with local beekeepers before applying an insecticide to alfalfa.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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