Sunflower-Stem weevil

Black sunflower stem weevil (Apion occidentale)
Sunflower stem weevil (Cylindrocopturus adspersus)

Pest description and crop damage Black stem weevil adults are black and 0.1 inch from snout tip to abdomen tip. The very narrow snout protrudes forward from the head, which is small in relation to the rather large, almost globose body. Larvae are 0.1 to 0.12 inch in length at maturity, C-shaped, and yellowish. Sunflower stem weevil adults are about 0.19 inch in length and grayish brown with white spots of various shapes on wing covers and thorax. The snout, eyes, and antennae are black. Larvae are 0.25 inch in length at maturity. They are creamy white with a small, brown head capsule, usually found in a C-shape in the sunflower stalk. High infestations (25 per stem) of stem weevils interfere with nutrient and water transport, stressing the crop and reducing seed yield and oil content. Both species may transmit Phoma (black stem) disease.

Management-chemical control

  • carbaryl (Sevin) at 1.0 to 1.5 lb ai/A. PHI 60 days. REI 24 hr.
  • deltamethrin (Delta Gold 1.5 EC) at 0.012 to 0.018 lb ai/A. Do not apply more than 0.045 lb ai/A per season. Do not graze or feed treated foliage to livestock. PHI 21 days. REI 12 hr.
  • esfenvalerate (Asana XL) at 0.03 to 0.05 lb ai/A. Do not exceed 0.2 lb ai/A per season. PHI 28 days. REI 12 hr.
  • lambda-cyhalothrin (Warrior II) at 0.02 to 0.03 lb ai/A. Do not apply more than 0.12 lb ai/A per season or more than 0.09 lb ai/A after bloom begins. PHI 45 days. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6 to 10 fl oz/A. Do not apply more than 0.12 lb ai/A per season of lambda-cyhalothrin or more than 0.2 lb ai/A of chlorantraniliprole. PHI 45 days. REI 24 hr.