What can I do to save the tree?
Ends of leaves have turned brown and curl.
Fuzz white nodes on underside of leaf at the apex of main vanes in the leaf.
Thank you for contacting the Toronto Master Gardeners.
You mention that your oak tree has white fuzzy nodes on the underside of the leaf. If this is the case then your tree seems to have oak flake gall which is caused by a gall wasp. There are many different types of leaf galls. Sometimes there are several different leaf galls on one tree. Generally, however, leaf galls are a cosmetic problem only and do not adversely affect the health of the tree.
From your second photo it appears that your tree is suffering from Anthracnose. Anthracnose usually becomes apparent during wet weather, which we’ve had plenty of this spring. The young leaves are blighted as bud break occurs or large dead areas form between the leaf veins primarily on lower branches. After some time slightly raised, brown dots (fungal fruiting structures) form on the lower surface of leaves and on dead twigs. With Anthracnose the lower branch leaves are most affected. Affected leaves appear to be sun scorched. Anthracnose is rarely a serious problem.
I am attaching a visual guide on the Problems of Oak.