Horned Oak Galls on Pin Oak: Same Pest, Same Approach

Identifying Spiny, Woody Galls on Northern Missouri Pin Oaks

Large, brown, golf-ball-sized growths with toothpick-like spines protruding from pin oak twigs in northern Missouri are horned oak galls, induced by the cynipid wasp Callirhytis cornigera. The woody interior houses developing larvae over a two-year cycle.

Key Facts

• Primarily affects pin oak and red oak species.
• Heavy infestations disfigure trees, weaken branches, and can kill trees over time.
• The wasp does not sting humans.
• Life cycle spans two years with alternating leaf and twig gall generations.

Practical Management

No insecticidal control is currently recommended due to the wasp's protected development inside galls and difficult spray timing. The most effective action:

• Prune out and destroy galls during dormancy (winter) before horns appear and wasps emerge.
• Maintain tree health with proper watering and fertilization based on soil tests.
• Accept that light infestations are largely cosmetic and do not threaten tree survival.

For visual reference, see the Tulsa Master Gardeners horned oak gall page.