Ornamental & Tree Diseases

This spring the leaves on my oak trees developed circular raised areas, about one-fourth to one-half inch in diameter. Does this indicate a disease, and if so, will this condition get worse and kill my trees?

The problem you're describing is oak leaf blister. This is a fungus disease and easy to diagnose because of its distinctive symptoms. While the leaves will grow abnormally, oak leaf blister isn't going to kill the tree, nor will the disease become more severe during the remainder of the year. It's too late to do anything about oak leaf blister at this point in the season, and the best approach is to start an oak leaf blister control program early next spring before leaf emergence.