The best way to gather the stems so that you avoid losing weevils is to grab the tip of the stem in one hand and break or cut the base of the stem with the other hand. Place the stems in a 5-gallon bucket and beat them against the side. Large larvae will be dislodged easily, but you also must pull apart the youngest leaves to find larvae feeding at the stem tip. Determining control strategies . If two or more larvae are found per stem, and 40 percent of the stems show leaf feeding, the best option is to cut the hay within 5 days, if possible.
Early cutting is a cultural control that avoids the use of insecticides.
If the alfalfa will not be mature enough to cut within 5 days, chemical control may be an option. Entomologists at the University of Nebraska have developed economic thresholds for alfalfa weevil. To use the economic threshold chart, determine the control costs in dollars per acre and then estimate the forage values in dollars per ton. The point where these intersect on the chart gives you the average number of alfalfa weevil larvae per stem needed to justify alfalfa weevil control. If the weevil count is below the economic threshold, resample the field in 3 to 5 days.