By Anthony Hanson
It's been a relatively slow alfalfa weevil season compared to previous years, though some reports of high population fields have trickled in during June. Most are mature larvae (i.e., fourth instar) that should cease feeding soon, but there are still some younger larvae present in samples (Fig. 1).
While I've been finding larvae regularly in west-central MN, I haven't seen large enough populations that quite reach an economic threshold and financially justify a insecticide application. This has been the case this year across the state when I've checked in with other extension educators and crop professionals. I would not be surprised if there are scattered fields that have reached threshold, so be sure to scout individual fields. Many growers should not need to spend money on insecticide this year though.
Source : umn.edu