I have hickory tree about 25 ft tall and for about 2-3 yrs it does fine until about mid august, then the leaves turn brown and curl. Poor tree is under stress and I don't know what to do.
that is my definition of drought
Hickory trees are likely to be harmed by fungi. Check the other leaves if there are spots. These spots are indication of fungi. Do you have any pictures of the tree? Hickory trees can catch diseases especially if it's planted without enough ventilation.
Sounds like scab which doesn't really affect anything but the appearance of the tree. It's more prominent during humid years. Your tree will be fine. Some hickory trees are more resistant than others also.