I think Pat hit it on the head. Plum curculio makes it almost impossible to
grow plums here without lots of spraying - dormant oils, spring oil with
diazinon, manzeb... If you don't, the opportunistic brown rot will destroy
the whole fruit, and the next, etc. You've seen the results. Consult your
extension agent for what is the best spray and timing for your area.
Gary

"Pat Kiewicz" wrote in message
...
mickeblue said:

can anyone help me out with a problem on my plum trees?

http://homepage.ntlworld.com/mickeblue/plums.html

The most immediate suspect is the plum curculio. This weevil lays its
eggs
on stone fruit and apples, leaving small cresent-shaped scars. The larvae
feed inside the fruit. The damaged fruit is then subject to various rots.

See:
http://www.uky.edu/Agriculture/Entom...ruit/ef202.htm

The control info here is short but very much to the point:

http://ohioline.osu.edu/hyg-fact/2000/2043.html
--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)