Ok will look it up. Thanks.
Does anyone know how it gets canker though? It’s fairly new, could it have had it from the supplier already, is it just had luck, is it bad conditions? I’ll do some tease arch soon. Thanks.
Fungus. It spreads via spores, although there is a bacterial form. Yours is most likely to be fungus. RHS is your friend, I'll put a quote and a link to their page on it at the bottom of my reply for you.
Do an internet search and compare the pictures to your pictures. It's really close.
Well what you need to be worried about primarily now is infection via you and water splash to the other plum and other parts of the plant. Think the common cold. Aerosol, rain splashs, or contact contamination aka your mucky paw. And you will get mucky paw if you use heal and seal- wear old clothes and gloves.
It's easily spread and it's in the natural environment already. It gets in via cuts in the bark. I'm not an expert but drought can cause bark to split if the tree gets too dry. And there was a rather dire drought last year so it probably got into your tree then and being under stress it's immune system would have been stymied because it wouldn't have had a lot of water to produce sap.
But how it spreads is why it is
so important you sterilise your tools and why you have to ensure you catch all the prunings . If you leave a bit on the ground, it'll act as a reservoir to infect the tree again. You touch the bark with your hand then touch another part of the tree and you risk introducing spores to a previously uninfected area, causing another infection. Rain splashing on the tree will cause the spores to spread as well - why we went for heal and seal to keep the area clean. The rain infection vector is probably why it's having such fun going down your plum's trunk.
Ours probably got it from birds going from a very infected tree several plots along. It's an abandoned plot and the tree is a total poxy mess.
You need to cut it out and DO NOT STAB YOURSELF. We wore safety glasses, had safety gloves, made sure we had a phone that was fully charged, Husband and I was up there so we had backup if stabbing happened. We also brought tea/biscuits as it was stressful. This is not a comprehensive safety list but me sure of your safety. Do your tree surgery it when it's dry and preferentially been dry for a few days and look for dark spots in the living wood, get them out too. Those dark spots are the fungus having a good burrow into the wood. Look at Huw Richard and his Dad's video on You Tube, their how I know this to tell you.
It could have had it from the supplier, see what your supplier's returns policy is though because that is a really bad infection. Don't feel bad at having missed it as it's easy missed if you don't know what your looking at and you find out by encountering it.
I was working clearing the area around "our" new apple tree for several weeks before I heard someone on GQT asking what killed my neighbour's apple tree? Was it my pruning? The panel said there's a dark spot on the trunk and it's probably that rather than your pruning. That was when I realised hang on, there's a dark spot on the trunk of "our" tree. The "support's" tie had caused a rubbing wound on our tree which led spores in. Finger's crossed both our tree's live.
Feel free to ask all the questions you need, we just went through this in August.
RHS link
https://www.rhs.org.uk/advice/profile?pid=86Here is their definition, there's a load more on their page. I advise you read it, they won't lead you wrong.
What is bacterial canker?
Bacterial canker is a disease caused by two closely related bacteria that infect the stems and leaves of plums, cherries and related Prunus species.
Cankers begin to form in mid-spring and soon afterwards shoots may die back. Shotholes appear on foliage from early summer.