Keep Scouting for Alfalfa Weevils

Alfalfa plant that has numerous holes in the leaves.
Figure 1. Alfalfa that has been heavily defoliated by alfalfa weevil larvae. Courtesy: Whitney Cranshaw, Colorado State University, Bugwood.org.

Originally Submitted: July 1, 2021

This week I received a report and picture confirmation of early-instar alfalfa weevil larvae in an alfalfa field. Although most alfalfa fields were treated for alfalfa weevils before the first cutting, those fields still need to be scouted. We are unsure as to why we are seeing a population of weevils, as there is only one generation of alfalfa weevils per season. However, we do know that there are two overwintering strategies used by alfalfa weevils, which may explain why we are observing another population of larvae. These alfalfa weevil larvae are just as capable of causing defoliation as the first population that caused issues earlier this year.

If you are observing defoliation, or if your alfalfa field begins to turn white (Figure 1) ,make sure to scout for alfalfa weevils. For more information on alfalfa weevils, scouting and thresholds, please visit our article, Alfalfa Weevils Are Active, and It’s Time to Scout, which covers all of these topics. If insecticide management is necessary for a field, be sure to review the pre-harvest interval to determine when the alfalfa can be cut.

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