How to Manage Pests

Pests in Gardens and Landscapes

Drippy oak (Drippy acorns)—Erwinia quercina

Drippy oak or acorns is a bacterial disease causing a clear to brownish, viscous liquid to drip from live oak acorns, leaves, or twigs. Dripping can occur after wounds to the oak caused by cynipid gall wasps, filbert weevil (Curculio occidentis), filbertworm (Melissopus latiferreanus), and possibly other insects. In at least some cases, the bacterium Erwinia quercina is involved and this bacterium is common where oaks occur. Honeydew-producing insects (such as aphids, scales, and whiteflies) can also produce dripping oaks, but these insects can be observed in abundance when they are the cause.

Solutions

Drippy oak does not appear to threaten tree health. The drippy liquid can readily be washed away with water or soap and water when it is fresh. No controls are known for preventing dripping caused by the Erwinia -insect interaction. Dripping usually stops within a few weeks. Sensitive surfaces beneath dripping plants can be covered. Alternatively, branches overhanging sensitive areas (such as patios and driveways) can be pruned off if this is acceptable and pruning is not so extensive that it will seriously injure the tree. No other control is recommended in landscapes.

Stunted acorns exuding liquid
Stunted acorn exuding liquid on a coast live oak with drippy oak malady.

Drippy oak acorn
Acorn exuding froth and liquid on a coast live oak with drippy oak malady.

 


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