Plum tree with damaged fruit

Thanks everyone, I like the idea of the grease band.

Haven't had a single bad plum this year and my DD's plum tree is the same. We reckon it was the unusually freezing weather in the spring that killen off the bugs.

The moths climb up in the autumn so you need to wrap a grease band around your tree. That will stop the blighters,

This happened to us last year. There is a moth that appears around blossom time that lays eggs. We researched the spraying to get rid, but decided not to bother and just enjoy the tree. This year, however, the fruit have been completely worm free with no intervention from us.
The only thing I can think of that’s different is that we had a nearby eucalyptus tree cut down. Maybe the tree encouraged the moths.