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.
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.