What's eating my overcup oak?

Overcup oak is a robust, flood-tolerant native US oak. It shares common oak pests: caterpillars, gall wasps, oak lace bugs, scale, and acorn weevils. Deer browse young trees. A notable advantage: overcup oak has good resistance to oak wilt, a serious vascular disease that kills many other oak species.

Leaves eaten from the edges or completely stripped in heavy outbreaks; repeated defoliation weakens trees and reduces acorn crops. Bacillus thuringiensis (Bt) spray is effective on young caterpillars. Hand-pick egg masses in winter. Healthy established trees recover from one defoliation event.

Spherical or star-shaped galls on leaves and twigs; generally cosmetic on vigorous trees. No treatment necessary on established trees. Improve vigour through watering during drought stress.

Stippled, bleached upper-leaf surface with brown resin spots on undersides; heavy infestations cause early leaf drop. Knock off with a strong water jet. Apply insecticidal soap or neem oil to leaf undersides in late spring. Avoid drought stress, which intensifies damage.

Larvae inside acorns hollow them out; exit holes visible on fallen acorns, reducing viable seed. Remove and destroy fallen acorns promptly. Permitted insecticide at acorn development can reduce ovipositing adults on managed trees.