Sunflower XIV-12

Sunflower Root Weevil

Frank B. Peairs

Weevil adult, left; larva, right.

Field Biology and Identification

Adult root weevils are black, oval‑shaped and about six millimeters (¼ inch) long.  They have a short, almost blunt, downward projecting snout.  Larvae are creamy white with a small brown head capsule and about six millimeters (¼ inch) long at maturity.  Adults appear in fields by June. They can be found feeding on sunflower foliage in early morning and late afternoon.  Adults are often found around the root zone at the soil surface during mating.  Bright yellow eggs are deposited two or three at a time in stalk tissue.  Larvae can be found in stalks by mid‑July and by September and early October larvae form a "soil cocoon" around roots at a depth averaging two to five inches, where they overwinter.

Plant Response and Damage

Adults vector such fungal diseases as charcoal rot and Phoma black stem disease.  Numerous larvae in the stalk will cause serious stalk breakage. 

Management Approaches

Significant yield losses and stalk breakage have not been demonstrated with this insect.  Insecticide treatments are not considered necessary under most conditions.

Categories: Sunflower, Insects, Sunflower root weevil

Date: 04/16/2004