Alfalfa weevils are major early season pests that can defoliate entire plants if left unchecked. Because these pests overwinter above ground, mild winters can increase weevil survival, making them a top priority for growers.
Damage normally only occurs to the first cutting of alfalfa, but both larvae and adults may damage regrowth when populations are high, causing yield, quality and stand loss. Careful field scouting is key to spotting problems early.
“Nature does a good job holding weevils in check with predatory insects such as stink bugs and certain wasps,” said Matt Montgomery, Pioneer Field Agronomist. “While effective at holding this pest in check, Mother Nature is not foolproof. Collecting field samples can help determine if nature is helping or if alfalfa weevils require an insecticide application.”
Harvesting a weevil-infested field can be an effective control method, but alfalfa weevils may continue feeding on stubble and new growth. Fields should be scouted four to five days after the first cutting to determine if weevils are still present and feeding.
If adults are causing the majority of damage to regrowth, ensure the insecticide product is registered for adult control and applied at the proper rate.
After feeding, adult weevils will leave the field and enter a resting period until fall, when they return to lay eggs before the onset of cold weather.