Problem with ornamental plum
We own a flowering plum tree that is 15 years old and bears no fruit. It is one of four such trees in adjacent yards, ours being the last in the row. All four trees did bloom this spring as they have in the past, but not as magnificently as in prior years. Two years ago, in mid May, we noticed that leaves on all four trees were turning brown and shriveling. Ours was in the best condition, with all the others worse as we progressed up the row. We sprayed all the trees, and ours seemed to recover for the remainder of the season. The problem re-occurred last year, and again we sprayed three of the four trees, and ours seemingly recovered. Currently, the last tree, untreated last year, has no leaves. The other three are in varied stages of compromise. This time, however, the branches have leaves that are dry, and crumbly (shriveled like small dried flowers) and the only few healthy leaves are located at the top of the trees. We also have noted that the bark of the tree has splotches of a white and green filmy residue on the northeastern side of the tree. Is this a blight which ultimately will claim the tree--meaning it is just a matter of when the tree finally succumbs? Is this a disease that can be controlled, or is it time to remove the tree?
Without photos it is difficult to guess what the specific problem is with your plum. We are guessing that the growth that you describe may be a lichen, which is not what is causing the problem with the plum. http://extension.umd.edu/learn/i%E2%80%99m-lichen-it-peak-season-lichen-peeping The most likely problem would be borers. Once borers are inside the tree, there is no spray that will correct the problem. Scratch the bark of affected limbs with your fingernail. If there is green under the bark, there is a chance of life. If there is no green, get those portions cut out. Once the dead portions are removed, it is possible that what is left is so unsightly that you may want to replace it. If you still have a question, you could send us photos so that we have more information with which to work. vw