Gambel Oak Acorn Weevil: Soil Systemic for Edible Acorns

You want to harvest Gambel oak acorns in Colorado but weevils infest them. When do adults lay eggs? Can you treat organically?

Weevil Life Cycle

• Adults emerge early summer, mate high in canopy.
• Females drill soft-shelled acorns, lay eggs, plug with fecal plug.
• Larvae feed inside, exit at drop, burrow in soil 2–3 yrs before pupating.

Treatment

• Soil-applied imidacloprid (Bayer Advanced) in spring. Translocates to acorns; kills weevils/larvae.
• Labeled for fruit trees—acorn residue negligible.
• Organic? None effective. Orthene (acephate) foliar spray at 10-day intervals ×3 during adult flight—but hard to cover tall trees.

Bottom Line

Spring soil drench imidacloprid is best. Safe for eating acorns (labeled for fruit). Organic options impractical.