There are a few steps a gardener can take to save a diseased oak tree instead of cutting it down. Although resistant to some extent, oak is susceptible to fungal diseases that can affect its appearance and health when left untreated. Although infections and treatment procedures vary, you can restore the tree back to health. The success of treatment depends on the extent to which the infection has spread, the level and quality of tree care and maintenance and the resistance of the oak tree.
Spread a large tarp directly under the tree to collect cuttings. Inspect the tree thoroughly to determine the type of infection; whether it is on foliage, trunk or bark; and if it is concentrated in one section or spread all over. Snip off diseased branches or stems to prevent the infection from spreading to other parts of the oak tree.
Discard or burn infected branches immediately. Also, rake and burn fallen leaves, as they may contain the infection.
Spray the diseased sections with an appropriate fungicide. Follow label directions for use and precaution. Inject the tree with fungicide to prevent it from spreading through the vascular system, which could impede the passage of water and nutrients between the roots and the foliage.
Reduce stress to save the diseased tree from dying. Water the oak tree frequently and feed it a well-balanced (10-10-10) fertilizer around the drip line every month during the growing season. Mulch the area around the tree to keep roots cool and weeds from growing there. Space the mulch 1 foot away from the trunk.