Thats it. Prune out carefully and isolate or destroy immediately. Hate the stuff.
Its on the trunk. I don’t think I can prune it out. The Santa Rosa was bare root and has been in the ground for 15 months. Other question is should I be concerned for my peach tree?
Like Mrs. G said, prune it out which I’ll say in better detail then just that. Take a sharp pocket knife or something similar and use it like wood plane. Scrape the black knot and bark off at least 1 inch further then the infection in all directions til you are down to uninfected wood on the trunk. You also may want to put down some plastic or something underneath the area to catch the infected stuff you scrape off. This will not effect the tree growing more and anything that you scrape off, immediately remove from the area to the trash if you have garbage pickup otherwise bury it. Hope this helps some. I forgot to tell you that peach trees do not get black knot. 
They have or get other problems…lol
btw… don’t scrape all the bark off around the trunk, if you do you’ll kill the tree!
I doesn’t matter if it is on the trunk, it consumes the cambium so the bark beneath it is dead. Think of it as a cancerous tumor- you have to remove all of it ASAP. Use a sharp knife, even a razor knife works well. Cut outside of the gall to clean wood. Obviously you can’t go too far outside of it but even if you half girdle the tree, it will heal. It’s a healthy tree and the trunk will expand its diameter and close the wound so by summers end it won’t look too bad.
I manage a couple hundred plum trees at least and cutting out BK galls is a constant chore. 99% of them survive but many are badly scarred.
So here’s my game plan. Scrap away 1 inch from where the black knot is in every direction. I saw online that spraying chlorothalonil into the excised area might be worthwhile. Additionally, do I need to cover the wound with anything? Thank you!
I often spray wounds with chlorothalonil but I can’t vouch for its efficacy. Sprayed wounds have sometimes had recurring galls even when carefully removed. I’ve been doing some cutting the last few days and because its been windy we haven’t been bothering with the fungicide, but will probably go back to it when the winds die down.
Don’t cover the wound with anything else.
You might need to secure the tree for a while if your cut weakens the structure significantly. I’m getting into growing stone fruit and I’m sure it is just a matter of time before I have to do a similar removal. Hope your successful. Bill
So I found another area of black knot so I excised and shaved both areas. I am probably going to continue to spray chlorothalonil for the few days just to play it safe. I had to go fairly deep until all the “roots” of the fungus were removed. Thanks again for the help!
I would use a razor knife to make bark cuts as steep to the wood as possible so there is absolutely no bark partially shaved. Just healthy bark straight to wood.
Good suggestion! Thanks again!
My concern is that in the second photo the angles of the cuts into the trunk are too acute and forms a sharp “V” into the trunk wood. That sharp “V” point where the 2 cuts meet is strucurally weak. A more gradual rounded arch-like cut even if it covers a larger verical area would be better.
I think you can still “round out” the bottom and do it even now even if it extends higher and lower. The vertical height (length) of the trimmed area is not as important as the circumferance of the trim.
If you don’t want to do it, a piece of a flexible temporary brace (bamboo) of support while it heals and re-grows would help.It would help even if you do the modification
Just my 2 cents.
Mike
I agree that it was damaging and unnecessary to go so deep into the wood. If you get to clean wood that is where you want to go and no further.
Also that it might be wise to support it until it can grow major callous that will make it stronger than it ever was.
I just found one exactly like the photo near the bottom of the trunk of one of my Frankenplum varieties - Methley of course
It apparently started at the knot of an old pruning cut, which I had to saw to get at the canker
It went deep at one point, and I think I need to use a sharp chisel to be sure to get it all
As long as I had the bleach out there to clean the tools, I applied some to the wound, too
I believe the active fungus works on cambium and there will be no living fungus deep into wood.
I had hundreds of knots last year and based on the few that came back this year, all my mistakes were not cutting out enough either on sides or ends. Now that I have fewer I am being careful to cut out every little bit of bad looking wood plus a bit more.
Anyway I am agreeing with Alan that there is no need for deep cuts, just get the cambium. And get a little more for good measure.
Scott,
Ever try what that guy recommended about scorching the area after cutting away the bad part? Brady
I was about to try it this year but based on what I saw from the previous years mistakes I think just cutting a bit more will work as well and without the hassle. If I am proved wrong on that in the following year I may try burning it, it does seem like a reasonable method. One advantage of burning is if your knife was transferring some virus to the outer wood it will get killed in the burning. I am now trying to cut out bit by bit so by the time I am all the way out on the edge the knife is clean.