Here in Rogers County, Oklahoma we just experienced a cool, wet 2016 spring season. Now it is June, and the precipitation has switched off and the heat has turned on. The result . . . trees are suffering from the extreme weather swing and are shedding some leaves, not all, just some.
Solution? Don’t panic! Rake up the leaves ASAP, especially if fungal leaf spot is detected as pictured below, and water weekly with a soaker hose around the drip line of the tree if drought and high temperatures persist.