I have a plum tree that has Black Knot and has had Black Knot more than once. Each year I spend a bit of time cutting out the knots, now that I am getting into grafting I was thinking about cutting it back as far I can and try to graft plum scion wood that is least resistant to Black Knot. My question is, is grafting into an initial graft that has had Black Knot with a less resistant plum grafts, going to end up in the same boat?
If you graft a new scion variety that is susceptible to black knot, the scion will probably get infected. Not necessarily through the original wood, but just from the same outside conditions that caused it on the original tree. It wouldn’t hurt to graft resistant scion varieties onto your tree. However, I would say cut and spray your existing tree as needed, and in the mean time plant a President and a Blue Byrd. They are supposed to be black knot resistant, and I haven’t had any on my trees yet. Then you can graft other plum varieties onto these. On my other plums that have black knot, I’ve been cutting and doing dormant sprays with copper, and trying to spray early spring with chlorothalonil before any fruit forms, and again in the fall. It seems to have slowed down black knots by at least 75%, but I’ve only been doing this for a few years and there could be other reasons for the slow down. I’ve also had only one small knot on 1 of 3 Jefferson plums I’ve planted, so I think it is a good variety (Trees of Antiquity usually sells it). Also, so far so good for Early Laxton and Geneva Mirabelle, but again, it has only been a few years. My worst has been Rosy Gage. I cut out so much the first year I didn’t think it would survive. Been spraying it with copper and chlorothalonil and it is doing good now, just looks really gnarly. If you know of any other varieties that seem resistant, let us know!
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Ztom,
Thanks for the feedback. I will be looking for some plum scion for next year and hope to get more control on this fungus.
thanks
Bob