I can't help but wonder if the ants aren't just taking advantage fo the dead wood? I don't know though.

Precisely.

Plums are subject to a number of diseases around here.
I don't know the situation in your region; perhaps someone will enlighten us.

The ants are a symptom of a problem, not the problem. You need to find out why they are in that tree which may be the result of a disease or simply because rot got started for any number of reasons such as bad pruning.

Tom, I know that it is alarming to see those ants swarm from your tree, but everyone is right: the ants are the messengers and you know what is said about those guys, lol.

Carpenter ants can't and don't chomp through live wood. They will, however, take advantage of internal decay, such as heart rot of trees. This systemic fungal disorder (quite common) is introduced into a woody plant a variety of ways....improper pruning, storm damage, insect or animal damage.

Carpenter ants are only considered a pest when they enter and set up housekeeping in our structures. In their native environment they perform an important service, nesting in rotting trees, stumps, fallen trees, old fence posts, etc. They don't feed on the dead wood, by the way. They just follow the diseased channels, hollowing them out to make room for the colony.

Your tree sounds like it has been diseased for some time. There is nothing that can be done for internal heart rot, by the way. It's possible for an otherwise healthy tree to live for many years....generations in some species.....but yours sounds like it is in serious decline. You can't 'fix' it.

There is NO chemical treatment for the fungus. Maintain a good layer of mulch over a wide swath of soil around your tree, water during periods of drought. You might want to send pictures of the whole tree so that I can see the extent of decline.

all ornamental plums are what the tree peeps call SHORT LIVED TREES ... [and so are most fruit trees] ...

in my experience ... 10 to 15 years at max ...

you are at 20 ...

get rid of it .... its not worth the effort ...

cut it to the ground.. and apply stump killer or round up.. to the cambian layer ...

if you insist on another.. just dig a hole a few feet away from the stump ...

ken

Thank you all for the quick advice. It makes sense the ants are just taking advantage of the dead wood and "doing their job." I guess I will start planning on a replacement tree.