It has a walloping case of black knot fungus and is likely so deteriorated that it is not worth saving. Might start planning for some sort of replacement tree now.

Thank you!

Is there a way to treat the area to prevent infection of future trees?

not unlike flowering cherries.. plums are basically short lived trees ... if you get `10 years out of them you should consider yourself lucky ... and it appears this tree might have got an extra 20 .... so 2 green thumbs up for it ...

that said .... it is time to plant another tree .. personally i would recommend against another plum ... per the above ...

btw... is this a fruit production tree??? ....

we speak in tree time with trees... usually counted in decades ... this thing might stand there for another ten years ... which reinforces the idea of getting something else going to the sight block .. while this one falls apart ... no real need to get rid of it immediately ...

i am aware of no other tree or plant affected by black knot ... and i ran a quite diverse 5 acre garden ... so that is not a reason to get rid of it immediately .. unless you have some plum collection or some such ...

with disease and bugs in the garden.. we talk of integrated pest management .... which means on one level.. just minimally reacting to exisiting problems .. and not nuking the garden all the time.. for what may or may not happen in the future ...

so.. here.. the bottom line is... if you have a problem with plum in the greater area.. dont replace it with a plum.. and problem solved ...

and if you plant a new tree .. mother earth net zero .. and no further tree hugging necessary ....

good luck

ken

for future reference: https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub

Black knot can affect cherries and plums (both fruiting and ornamental), apricot and chokecherry.

This tree had some fruit last summer but not many.
Glad to know that it won't affect non fruit trees. We will probably plant some kind of Japanese maple, they do great here

Usually the easiest trees for your area will be natives. Not sure your location but there are undoub some nice ornamentel natives wherever you are