– Kyle Verhoff, Jason Hartschuh, CCA, Emma Matcham, Aaron Wilson, Kelley Tilmon, Ohio State University Extension
Alfalfa Weevil damage and larvae
Despite the chill in the air, overall rising spring temperatures are beginning to bring activity back to our fields. The good news is that we get to scratch that itch and get more active in the field; the bad news is that our pests get to be more active, too. Alfalfa weevils are one of the two key alfalfa pests in Ohio. By utilizing growing degree days (GDD) and simple scouting methods, we can estimate weevil activity and minimize the potential damage to our first cuttings of alfalfa. Alfalfa weevil adults (and some eggs) overwinter in Ohio and increase in activity when temperatures exceed 48°F. Since alfalfa weevil overwinters, older alfalfa stands are more likely to be affected since previous populations of alfalfa weevil have had the opportunity to establish and overwinter nearby. The larval forms of alfalfa weevil are more damaging than mature weevils since larval feeding on foliar tissue causes the most damage to the alfalfa stand.
As GDDs accumulate, the larvae continue to grow and are most damaging at the later larval stages (3rd and 4th instars). Peak larval activity and feeding damage are at their highest when heat units for the area are between 325 and 575 (accumulation from a base of starting at 48°F January 1st). As of writing this (Jan. 1 – April 5), heat units range from 136 in northeast Ohio to 295 in south central Ohio. We are at or slightly ahead of . . .
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