Plums often thin themselves in June, its called June drop. If the plums are still really small they may just have not pollinated properly; the aborted ones change color and fall.

Scott

Isoh, I have the same problem I sprayed with triaz. just yesterday and overnight the bottom of many of my plums have turned deep black/purple and are soft. Too much spray? This has never happened before. My crop is quite large so I expect June drop. But it looks as if my spray had some affect on the plums. Ugh, Mrs. G

One effect of infestation by the larvae of pests like PC is premature coloring, followed by drop.

Thanks much for the quick responses.

I'm a beginner, so m perception may be wrong, but I wouldn't say they are small. They are about the size of a small chicken's egg.

Only the bottoms are purple, so far anyway.