Issue No. 9, Article 5/May 21, 2004
Remember to Scout Alfalfa Regrowth for Signs of Alfalfa Weevil Damage
Just a brief reminder about alfalfa weevils: They are still out there! A few responses to last week's article in the Bulletin titled "Where Are the Alfalfa Weevils?" have indicated that alfalfa weevil larvae are present and feeding in some fields in northwestern Illinois.
In fact, some fields were nearing the economic threshold of 25% to 50% of leaf tips skeletonized and three or more weevil larvae per stem. As infestations near economic levels, management decisions must be made. One option is to harvest the crop as early as possible. Cutting the hay removes food and shelter from the larvae and exposes them to harmful rays from the sun. Remember to scout alfalfa regrowth for signs of alfalfa weevil damage! Larvae and adults have the potential to prevent or slow regrowth by feeding on new shoots. Control may be warranted after a cutting when feeding is occurring on more than 50% of the crowns and regrowth is prevented for 3 to 6 days.
Defoliation of alfalfa by alfalfa weevil in Whiteside County.
If early harvest is not possible, or an insecticide application is chosen as the management tactic, do not apply during bloom. Please refer to the article from issue no. 5 of the Bulletin titled "Degree-Day Accumulations and Economic Thresholds for Alfalfa Weevil" for a table of recommended insecticides for control of alfalfa weevil larvae.--Kelly Cook