Warm weather at the end of March prompted alfalfa weevil larvae to start feeding early, which means growers should be scouting their crop.

Anthony Ohmes, University of Missouri Extension agronomy field specialist, says April is the time to walk alfalfa fields to look for larvae activity.

“The economic threshold for alfalfa weevils is an average of one or more larvae per stem, and 30% or more of the plant terminals show feeding damage,” Ohmes says. “If the field’s infestation exceeds this, it may be time to start spraying.”

Spraying do’s and don’ts

Always read and follow insecticide labels to ensure proper treatment. Some factors can reduce the efficacy of insecticide applications to control alfalfa weevils. These include:

Alternate options for control

If farmers do not want to spray, there is another weevil management option: Harvest early.

“Remember, it is best for the crop not to harvest earlier than seven to 10 days before the normal growth stage of one-tenth bloom,” Ohmes says. “This harvest could be done by hay-cutting or by grazing.”

MU Extension research has found that mechanical harvesting or grazing cattle can reduce 90% or more of the weevils.

If grazing, be cautious of bloat from wet foliage and damage to the crowns from trampling during wet conditions.

Source: University of Missouri Extension