Have a flowering purple plum tree, the braches have whie residue on some and then the braches are gettig black

Best to take a piece of the branch to a real nursery (where do you live?). I have 25 young flowering plums at my ranch who are real happy it's spring. The white stuff residue is probably pests, maybe fungus but don't think so (have seen the same on rose bushes, akin cousins to flowering plums, they like the same conditions). You might not even be able to SEE them, but they're spinning that white stuff on your pretty tree.. The black from the normal red is that the sap is stalling out (tree -%26gt; cough die). Not professional but you get it.

Have a flowering purple plum tree, the braches have whie residue on some and then the braches are gettig black
fire blight or black knot....








http://pubs.caes.uga.edu/caespubs/pubcd/...





http://www.treehelp.com/trees/cherry/tre...





if neither of these seem to be the problem, take a sample in a sealed baggie to your County Extension Service office for identification.... do it soon.... it only took two seasons for us to lose a plum once the branches started going black.....