Folks, could you please take a look at the picture below and let me know if this is black knot on my plum tree or a die-back from past pruning? And if it is the black knot, can I excise is and save the branch (given that it only affects a side of the branch)? This is a multi-grafted tree and this is the only Seneca branch on it (and I love its fruit!) Many thanks for your thoughts!
There is nothing there that would indicate that it is black knot. Seneca has some resistance to black knot but is not immune. Ordinarily I would prune the injury out but since your wanting to keep it because it is a graft you could just leave it . Should heal up on its own. Keep an eye on it though. If you decide to prune it out it would be best to do it while its dormant.
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Thanks for the quick response, I hope you are right! But if not black knot, what do you think this might be? The more I look at it the more I think it’s not just a die-back, because I would not have left such an untidy cut. And it does look like there is some growth on the bottom of the wound.
Its difficult to tell from the picture but it looks like an old pruning cut that did not begin sealing properly. Maybe too long of a stub. Winter injury may have happened too. Hard to be sure.
This actually looks like Black Knot to me, in early stage of development. It will start turning black afterwards.
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Thanks! It looks like there are differing opinions about this on this forum, so it’s not just me and my wife 
. For now, we just carved out the (diseased?) wood and will monitor how things develop. To @tennessean’s point, we did discover a knot behind the removed wood, so there must have been a branch sticking out from this spot that was removed at some point (as he surmised). And I do tend to leave longish stubs when pruning, having read that this prevents the die-back going back beyond the attachment point of the removed branch. Sounds like it’s another thing for me to learn more about!
It may not have started out as Black Knot but it looks like thats what it turned out to be. If you just trimmed it out hopefully you also included a fungal treatment like Oxidate or copper.
I had trees of Seneca and Valor that I fought BK with for years. Both large trees, Mariana and St Julian rootstocks. The Seneca I finally had to give up on and take out. The Valor I took out cause it just was too big. I have a commercial dehydrator and used to do a lot of both those varieties … mmm… just thinking about them makes my mouth water!
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Is Black Knot present in the west cost? I thought (not based on any reading) it exists east of the Rockies only.
“If you just trimmed it out hopefully you also included a fungal treatment like Oxidate or copper.”
I thought you only apply copper at the end of winter? Is it OK to apply now?
That only applies to spraying the foliage. You can mix up a small amount , tiny amount in your case, and brush it on to the site.
Well i can only speak for coastal Washington but it is definitely prevalent here.
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Well, I am east of the Rockies (in NE Ohio).
My cherry tree definitely gets a touch now and then.
Scott smith swears by torching away black knot.
Here is his post:
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Black Knot is extremely destructive. My 14 year Methley plum tree is covered with it. Pruned it out last February but it came back worse than ever. Its defoliating something horrible and I see small branches dying. The BK did not keep it from producing way too many small plums which the raccoons are feasting on. Did can a small batch of jam last night. Tried the hot gun several years ago and that seemed to help some. Probably will use a chainsaw on the tree after the plums are gone. Get tired of fighting the stuff.
I’m not quite understanding how in northern latitudes growers prevent freezes from killing the blooms each and every year. I’ve had that trouble here in past years and I’m in the south.
It’s not just how far north you are, it’s the spring weather patterns. In particular how big the temperature swings are given how far along the blooms/fruits have progressed. Tennessee is one of the worst for early freezes from hearing various reports here over the years. Kansas is also pretty bad. Michigan is far north of you, but the western shore is covered with cherry orchards since the lake there moderates the temps.
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