The best defense against a range of plant pathogens and insect pests is to promote tree health. The following are some general guidelines.
Irrigation Avoid frequent irrigation of oak trees.
Oaks are adapted the dry Mediterranean climate that prevails in central coastal California and most established oaks do not require supplemental irrigation except under severe drought conditions. Consult with a certified arborist or other specialist for advice if extreme drought conditions occur. Do not damage the roots by activities such as paving and soil compaction. Apply a 4 - 6 inch deep layer of mulch under the tree canopy. Fertilization Fertilize if the tree shows external symptoms of deficiency, such as yellowing of the leaves, and the deficiency is confirmed by a laboratory test.