Black Cherry tree has leaf tips turning brown

I have several bare root black cherry trees planted this spring whose leaves are starting to turn brown at the tips. Not all of the leaves and not all of the trees are doing this. I've heard that black cherry's can't get fire blight but possibly brown rot. It has also been a rather warm few weeks with no recent rain. I watered the trees last week since they hadn't had a drop in over 3 weeks. Could this be a blight or rot or just weaker trees from lack of water? Is there anything I can do? Any suggestions appreciated.
Locale: Montana, high desert, zone 4b.

Most likely what you are seeing is leaf burn from lack of water. You state that these were bare root trees planted in the spring, I doubt that the root system at this point is developed enough to sustain the tree for a 3 week drought. I'd water them at least once a week for the first growing season. To help them along, some B-12 dissolved in water will stimulate root growth, this works for any plant. The tips turning brown, with out other spots forming on the leaves is a good indicator of lack of water.