Hi Ed.  Thanks for contacting the UVM Extension Master Gardener Helpline.  I'm sorry about your curculio issue.

I'm attaching a selection of links with information about life cycles and IPM control.  There are other chemical controls out there, but since these are trees at a home, I'm assuming you'd prefer as low a toxicity level as possible.

Some of the articles are heavy on apple information because that's often the economic crop that's hit.  The same information works for all core and stone fruits including plums.

https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/insects/beetles/plum-curculio

https://extension.unh.edu/resource/plum-curculio-fact-sheet

https://extension.psu.edu/tree-fruit-insect-pest-plum-curculio
I hope this information is helpful.  Good luck!