Answer: I'm afraid you're right about removing the plum trees. Once bacterial canker or black knot fungus (both cause canker-like growths) has set in, there's no cure. However, there is prevention, which, as we all know, is worth even more! Look for plums grown on peach rootstock for maximum resistance. This is not a guarantee, but it's a great start. Make sure you prune branches properly to and otherwise minimize damage to the bark, which is where the bacteria enter the tree. The healthier they are, the more natural resistance they will have, too. There shouldn't be a problem planting your new trees in the same place. Check with your nursery supplier for an appropriate variety, or contact your extension fruit specialist at 608-263-2775. S/he can also tell you definitively where the pathogen "hangs out", and if it is truly safe to replant in the same area.
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