Here are some possibilities:

The majority of people can agree that oak trees are beautiful. But if they are left untreated, oak tree diseases will kill the tree. Many homeowners don't realize that their actions can contribute to a tree dying, so it is important not to make any changes to the canopy of an oak tree. Symptoms of oak tree diseases include discolored or spotted foliage, dead or dying foliage or branches, thinning canopy, shelf mushrooms or wet patches on the trunk. Although infections can lead to the death of a tree, one can treat them.

Phytophthora root rot is a disease that is soil-borne. This disease rots at the roots of the tree, and if the soil is warm or produces a lot of moisture, the virus can reproduce. Phytophthora can form if you water the oak tree beneath the canopy. Native oak trees thrive off of drought-like conditions. Another way that the tree can become diseased is if there is a buildup of soil or mulching material near the trunk. The disease thrives in this type of environment and is harmful to the oak tree's health.

Oak tree blister can be detected on the top and bottom of the tree's leaves. The surface of the leaves will look blistered, hence the name. On the other side of the leaf, it will look gray colored, but as the disease gets worse, it will turn brown. When the tree turns brown, it will curl up and drop prematurely. The tree won't die, but it will not be as full during the season as it should.

The most common type of diseases is Armillaria root rot, also known as oak root fungus. Oak root fungus is found in the root and tree trunks. If you see clusters of mushrooms growing at the base of an oak tree, this is a warning sign of oak root fungus. The health of the tree becomes compromised due to overwatering the tree, nutrient deficiency or excess soil build up. Interestingly enough, Armillaria root rot can last in a tree for over 20 to 50 years if left untreated.

Bacterial wetwood is the least damaging oak tree disease. Wetwood, also known as slime flux, is when an anaerobic bacteria infects the wood. The infected wood's composition causes disrupted membranes, high pH and low amounts of free oxygen due to small spaces in the tree being filled with water. Wetwood infects wounds, branch stubs, and root stubs, as well as alters the wood by causing high pH, high moisture and low oxygen due to decay-causing fungi. You'll notice the effects of wetwood because the tree starts to form a bunch of cracks called spider heart.

Other recommendations include, turn off the water. Don’t try to grow plants with high water demands under your oaks, particularly near the trunk. Even more important is to avoid frequent and shallow watering. You may have to choose between having healthy oaks or a green summer lawn in that part of your yard.

Protect the ground and tree roots from excavation and pavement. Avoid driving vehicles and tractors under the oaks. If you have an old oak in a new subdivision or where tree roots may have been damaged by nearby construction.

Majestic old oaks can add much to the value of your home and the pleasure of your yard. It is well worth understanding how to keep them healthy

Here are two publications you may find useful.

https://www.ces.ncsu.edu/depts/pp/notes/Ornamental/odin30/od30.htm

https://extension.psu.edu/oak-diseases

Hope this helps!