We have several dozen large and very old live oak trees with circumferences of 15' or more here on the ranch. Some didn't leaf out as usual this past spring. To make matters worse for a few of them, Blue Bonnet Electric, our service provider, is going to trim their branches back next month. As if they weren't stressed enough. Last year a few of the oaks dropped some large branches. Mostly likely as a result of the 2007 - 2009 drought.
We lost most of our water oaks to Hypoxylon Canker in 2004. Stress makes trees more vulnerable to diseases.