How to Manage Pests

Pests in Gardens and Landscapes

Oak branch dieback—Diplodia quercina

Oak branch dieback is a fungal disease that occurs on several oak species, including coast live oak, valley oak, black oak, and English oak. It causes leaves to wilt and turn tan or brown. Infected branches die, and if the bark is peeled back, infected wood is usually dark brown to black.

Identification

Solutions

Prevent branch dieback by providing trees with proper cultural care. Drought stress appears to contribute greatly to this disease. Even drought-adapted species may require supplemental irrigation if rainfall has been below normal. However, the irrigation of native oaks should generally be done during the normal rainy season to supplement inadequate natural rainfall. Oaks in disturbed urban soils may also benefit from irrigation around the drip line (not near the trunk) at 1- or 2-month intervals during the dry season. More frequent irrigation during the dry season promotes serious root diseases. Prune out diseased and dead branches from November through January; new infections are least likely to occur during that time. Fungicides generally do not provide effective control. The disease is not likely to be a problem most years and control is usually not needed, especially if trees are cared for properly.


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

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