My latest technique is the blowtorch method … it is a lot faster and easier. I just hit the knots until they start to sizzle. You need to be careful to only do one side of a limb and for not too long, otherwise you could girdle it. Also for smaller branches they need to be cut out.
Back on the original topic, the post @Stan mentioned is this one:
But if you go to the thread, the guy I was giving the advice to says he tried removing knots and there were too many so he gave up. He has a wild cherry grove nearby full of knot. So @anon89542713 I’m not sure how you will fare with plums, it depends how bad the knot is there and how diligent you can be on zapping the knots