Gray seed weevil (Smicronyx sordidus)
Red sunflower seed weevil (S. fulvus)
Pest description and crop damage Larvae of both species are small (0.12 inch long), cream-colored, legless and C-shaped. Red sunflower seed weevil adults are 0.1 inch long and reddish brown. Adults of the gray sunflower seed weevil are slightly larger (0.14 inch long) than S. fulvus and gray. Red sunflower seed weevils usually only partially consume seeds, but separating undamaged from weevil-damaged seed is difficult. Most larvae drop from the head to the soil after completing their development, but a small percentage may remain in the seed to pupate, and those can cause heating and moisture problems at harvest and bin-filling time. Growers who find a seed weevil infestation should delay harvest to allow most weevil larvae to leave the seeds. Seeds infested by the gray seed weevil lack a kernel and seeds may be lost during harvest, due to their light weight. Because of the gray sunflower seed weevil's low population levels and low fecundity, it usually does not cause economic damage, especially in oil sunflower fields.
Economic threshold Economic thresholds vary with differences in plant population, insecticide and application cost, and sunflower's market price. Currently, about 14 seed weevil adults per head in oil sunflower is the average economic threshold.
- beta-cyfluthrin (Baythroid XL) at 0.016 to 0.022 lb ai/a. A maximum of 0.22 lb ai/a per 7 days or 0.066 lb ai/a per season. PHI (pregrazing and preforaging) 30 days. REI 12 hr.
- chlorpyrifos (numerous products) at 0.5 lb ai/a. Do not graze or feed treated forage. PHI 42 days. REI 24 hr.
- chlorpyrifos + lambda-cyhalothrin (Cobalt Advanced) at 16 to 38 fl oz/a. Do not graze or feed treated forage. PHI 45 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.