How to Manage Pests

Pests in Gardens and Landscapes

Twohorned oak gall wasp—Dryocosmus dubiosus

The two horned oak gall wasp is a cynipid wasp that forms an oblong or round, seedlike gall. Galls occur on the underside of oak leaves, usually on a leaf vein.

Damage

Leaves appear scorched. Leaf margins are brown and dead beyond location of the gall. Some galls drop from leaves, leaving only scorched foliage. The gall wasp has two annual generations. The easily overlooked late-winter or spring generation lays eggs in oak catkins, causing catkins to distort into a club shape. Second-generation wasps develop in leaves.

Solutions

As with other gall wasps, no control is known or recommended. Because parasites are believed important in helping to limit this pest to occasional outbreaks, spraying may do more harm than good because pesticides can kill parasites and predators of gall wasps.

Galls on undersides of leaves
Galls on undersides of leaves

Scorched foliage
Scorched foliage


Statewide IPM Program, Agriculture and Natural Resources, University of California
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