Answer: Without seeing the tree, it's difficult to diagnose the problem. If the growth is on the leaves it is an insect gall caused by a wasp type insect. The galls will not harm the health of the tree but if they are in great numbers may cause the leaves to drop sooner than normal.
If the growth is on the trunk or bark area then it is either a lichen or the fruiting body of a decay fungus. If it is a fungi th wood under the growth will be soft. If so, the wood inside the tree may have decay fungus. This will eventually kill the tree because the inside will become hollow in 10-20 years. On the other hand, it could simply be lichen. If so, the bark and wood under the lichen be hard and solid, not mushy. Lichen grows on the bark surface and it will not harm the tree. Usually lichens are grey green in color but during the time they mature and send out spores, they can become quite colorful.
Blackened leaves may not even be related to what you see on the bark of the tree. A fungicide should protect the rest of the leaves but won't improve the color of the blackened leaves. You can prune away the dead leaves. Be sure to rake up any fallen leaves so the fungus does not splash back up onto the tree with rain or water from the hose.
Hope this information will help you determine just what the problem might be.
Q&A Library Searching Tips