That would be bacterial leaf scorch , and let me guess it defoliates in july/august and has worsened a little each year , starting at the tips and progressing inward annually , its a problem here and red oak trees have been dying left and right , there is no cure just try a deep root fertilization and hope for the best , Bottom line is that tree is on borrowed time ...Next you'll start to see the tree leaf only towards the inner of the tree often very thick , with leaves that are half green and half crispy brown ..... PM me if you need any other help with that tree GOOD LUCK