AgWatch

Short Residual Insecticide Recommended For Alfalfa Weevil

 LEXINGTON, KY.
   Tip feeding by alfalfa weevil larvae should be very obvious now. Late last week there were larvae of all sizes in Fayette Co. fields indicating that feeding could continue for up to more 10 days. A short residual insecticide can be used if there is significant weevil activity and a week or more until harvest. Small parasitoid wasps play an important role in regulating alfalfa weevil populations so insecticides should be used only as necessary to control large weevil populations. Check the product label for rates and harvest intervals and match times with anticipated cutting.
   Routine stubble sprays are not justified. However, if early harvest is used as a weevil management tool, there may be sufficient larvae or newly-emerged adults present to justify an insecticide application. Watch harvested fields carefully for the normal green-up that indicates active re-growth. Surviving larvae may feed on developing leaves and new adults can cause “notch-like” feeding holes on leaves giving them a feathery appearance.
   Treatment may be justified if adult weevils are found feeding on 50 percent or more of the crowns and re-growth is prevented for 3 to 6 days. Use low rates if an insecticide application is necessary. Δ
 DR. LEE TOWNSEND: Entomologist, University of Kentucky
Figure 1. Tip feeding by alfalfa weevil larvae.
Figure 2. Alfalfa weevil larvae.

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