From your description I suspect that you have a chokecherry tree. Their new growth is green, but turns maroon/purple at maturity. They also produce panicles of white blooms in spring.
Chokecherries are susceptible to a fungal disease called black knot canker. The source of infection is often wild chokecherry trees growing nearby. To control the disease, remove the galls (swellings on the stems) over winter, pruning at least 4 inches beyond outward signs of swelling. Cut out knots on trunks down into the wood, and at least 1/2 inch outward from visible swellings. In the spring spray the tree with a fungicide containing thiophanate methyl or captan just before the buds open then 2 more times at 7 to 10 day intervals.