I am surprised by your description that the tree is alive. Take a picture.

Karen: There is no effective treatment for the various types of fungal infections collectively called "gummosis". But you may not have it. It is unusual for a tree that young to begin to develop serious gummosis, and you may have only sap leakage due to physical injury, in this case freezing weather that may have split the bark just as sap was rising. I would probably remove the sap blob, but I do not favor use of commercial pruning sealers, since I believe they can do more harm than good. Since your tree is so young, it is likely to heal and close the sap leak on its own. I have seen this happen a quite a number of occasions. Definately thin your peaches as soon as you can identify the clear winners. Mine are pretty well done, and the peaches I left on the tree are growing quickly. I know it's hard to take them off, but don't leave too many peaches on a young tree. Don Yellman, Great Falls, VA

The link below will give you some information about prevention and treatment. Here is a link that might be useful: gummosis

It's probably the heat. Cherries don't do well in the heat. It should start to get better by the end of September if you keep the tree consistently watered. If you really wanted to go out of your way to tend to the tree, you could mist the leaves during the middle of the day (sometime between 12:00 to 4:00 ). I've even heard some people have very lightly sprayed their trees with mineral oil, or lightly rubbed some petroleum jelly onto the leaves, to help keep them from drying out. It's the height of summer right now, and a little browning is to be expected. San Jose has clearer skies than San Francisco, so less protection from the sun. In short, what you are seeing is perfectly normal for the climate you are in. There's a reason most commercial cherry orchards are based in Michigan and Eastern Washington. Also, in San Jose (all the paved surfaces in the surrounding area has an effect on temperature) it's quite likely your kwanzan trees are not getting quite the degree of winter chill that they would prefer. This results in slightly reduced vigor, and that is also associated with browning of the leaf tips. Your tree should fair better in future years when the roots have become more established (and they can provide a more adequate water supply to the leaves).