Any idea what plum disease this is?

I went on my daily orchard walk this morning and noticed a funny hard black substance growing on several of my methley plum branches. Google turned up a bunch of pictures but nothing appears to match. Any idea what this is? Odd looking plum disease picture.

That’s black knot. Do a search here. Basically the affected branches need to be cut out or the black growths removed to clean wood.

1 Like

Thanks fruitnut. I just read through the following thread [1] Scott started. If these are at the base of a large branch do I need to cut the entire branch out or can I just cut out the black knot with a knife? Also, would you recommend that I order some chlorothalonil and spray the tree? Man disease sucks. :frowning:


I should clarify one thing in my prior post. If I cut out the black knot should I spray the area where it was removed? I just pruned 4 - 5 smaller branches and I’ll cut out the growths from the other two areas to clean wood at lunchtime. Just wondering if I need to spray the areas where it was removed to kill any spores that remain?

Mickster I’m not sure but spraying the cut surface can’t hurt. Good luck and you are right this kind of thing $ucks big time.

Thanks fruitnut. Is chlorothalonil the only thing I can spray? Hopefully Alan and Scott will chime in since they’ve been through this before with their plum trees.

Chlory is the only thing recommended and it doesn’t seem to work very well as cutting out the galls is always part of the program.

Thanks Alan. So my best bet is cutting out the sections on the main leaders and making sure I get deep enough to remove it all?

I dealt with BK for the past 7 or so years. I’ve cut and pruned and sprayed and sprayed. Unfortunately it is a never ending battle. This year I’ve started grafting and will probably end up grafting on to the tree resistant strains of plums. So I’m cutting back a couple of trees next year to start the process. It has been a relatively rainy year so I get hit more it seems. If you maintain your trees relatively low to the ground and not let them get tall it is easier to prune out otherwise it becomes a chore, especially when you have several.

Best of luck.

Around here the persistence of BK depends a lot on the site, sometimes in mysterious ways (perhaps about the dew level). One thing is clear is that eastern exposure is very helpful. What I do is cut out the BK as soon as I see it and spray the wounds with myclo.

I use a sturdy and very sharp knife and cut beyond the brown discoloration of wood by an inch if possible, cutting cleanly down to wood so the bark is not tapered or beveled at all. If you keep at it you can usually get it under control except at the very worst sites. I have had to cut down a couple of Methely plums because they are the absolute typhoid Marys of BK.

Bluebyrd is supposed to be nearly immune and does seem resistant, but I was not particularly impressed with the quality of plums from a tree I have here that fruited for the first time last year. I ordered a bunch of them anyway to graft other varieties on.

1 Like

Here is a link to an earlier thread about Canker,where a flame is used after the area was cut out.Black Knot is also mentioned.I haven’t tried the method yet. Brady

I wrote that I sprayed wounds made when removing BK with Myclo- should have written Chloro.

Am I correct in assuming this is also black knot?


I’ve never seen it in person but yes that’s black knot.

1 Like


The black spots are last years and the brown ones are this years. I have had quite a bit of it in a couple varieties this spring: Golden Transparent Gage and Pearl. Cut cut cut! I don’t spray the wounds with anything, I am too busy and most of the time they heal over. Maybe 10-20% of the time I have to come back for more. Cut out all more-green wood you find, that is the live knot. The more of them you cut the better you can tell when you have hit the edge by the color change from a strong green to a lighter green.