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Alfalfa weevil pressure rising as MSU questions insecticide timing and resistance

A field crops entomologist says increased alfalfa weevil pressure this season could be a result of control failures.

Chris DiFonzo with Michigan State University tells Brownfield, “It was cold enough that the weather model said that egg hatch was just starting on weevils.”

“If you sprayed a couple weeks ago and you’re seeing weevils now, it might be that these are new ones that hatched in the meantime and you sprayed a little too early,” she says.

She says resistance isn’t out of the question.

“It could be, if you keep spraying your fields the last three, four, five years, and you keep spraying them with pyrethroids, you could conceivably create your own alfalfa weevil resistant populations,” she explains.

DiFonzo says disrupting natural biological controls like ladybugs and parasitoid wasps with unnecessary fungicide or insecticide use might also be a factor in the higher populations.