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