About a month ago, one of our oak tree's leaves turned brown all at once. Is there a disease or insect that would do this to the tree? None of the other oaks in the area have the same problem. Oddly enough it is next to another oak with a bunch of dead branches. You can see in the pictures. We also have a crab apple tree in the front yard that did the same thing. All leaves died on the tree at once. Some have fallen. The leaves didn't turn, they just died on the branches.