I would remove and dispose of it. Burning will work, but I personally would stay away from the smoke, and keep it from other plum trees. I think a hot
compost would work, but it would have to be
hot.
I think I would probably treat this like I would something like a cedar rust on
apple.
I would remove the affected branches and dispose of them, and then mix up some aerated compost extract and douse the tree and all around it for as long as the extract held out.
Then I would mix up some more and get all the rest of the trees that could potentially harbour the contagion.
Then I would mix up some more and start from the beginning, all over again. At least twice in a season.
I know that some contagions, like mosaic virus, are easily spread downwind by the smoke of burning infected plants.
Glad to hear you've gotten ahead of it, Tim. Please keep us posted, and good luck in the future.
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein