The message
from "David W.E. Roberts" contains these words:

It looks as though there is a ring of sorts centered on the Victoria plum
tree.

Coincidence.

Now I though that fairy rings were generally the slowly expanding circle of
underground fungus from a point source, often based on buried dead wood as
the starting point.

Yes, and no. Mushrooms which grow on rotten or buried wood (eg, Pluteus
cervinus) don't form rings, though they might if they started as a point
source on a buried forest....

In this case it looks as though there is a ring of sorts arounf the plum
tree.

Does this suggest that the roots of the plum have a problem around where the
ring is?

No.

The tree sems O.K. but is not as sprightly as it has been - I suspected lack
of nutrients (based partly on the spread of roots from all the trees, as
evidenced by suckers springing up all over the garden).

Cut suckers off - they are rootstock and are unlikely to bear fruit, and
if they do, it won't be Victoria plums. A dressing of well rotted
compost mixed with bonemeal spread over (say) a circle round the tree
extending to the width of the top-hamper - in the autumn. The worms will
come up for the compost and take the bonemeal down.

Is this ring evidence of a more serious problem, and if so what (if
anything) can I do about it?

No. As far as the tree is concerned, you can ignore it. The mushrooms -
well, the mycelium is living on decaying matter in the topsoil.

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/