As the number of warm, spring days add up, alfalfa growers in Indiana will want to begin scouting fields for alfalfa weevils, says Christian Krupke, Purdue University Extension entomologist.

In early spring, alfalfa weevil larvae hatch from eggs deposited in plant stems and begin feeding within folding leaves at the growing tips. A heavy infestation of larvae can consume enough foliage that an entire field takes on a grayish appearance.

“When you can see the damage from the road, and the field starts to look gray, you’ve missed the opportunity to treat with an insecticide,” says Krupke.

To scout for the pest, walk a field in an M-shaped pattern and examine five alfalfa stems from five areas of the field, Krupke advises. Look for evidence of larvae feeding – he recommends unfolding developing shoots to look for pinhole feeding and small larvae. As larvae grow, they will start to chew larger holes that make plants look shredded. Adult feeding damage looks like small, circular cuts along leaf margins, but is typically not a concern.

Producers should also look at the maturity of the stem (pre-bud, bud and flowers), stem length and average weevil larvae size.

For treatment strategies and other information about the pest, check this Purdue fact sheet.

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