Mixing Neem with Copper (or anything?)

Hello,
I have a couple of plum trees that just started producing two years ago. Unfortunately, despite my best efforts, the bugs get to the fruit and kill it before it matures. Last year, while my red variety of plums were still green, something pierced the tops of each little plum right on the top of the plum just a few MM from the stem. Every single plum dropped to the ground. I didn't get one.

I have heard that neem oil is great for fruit trees. However, can I mix it with anything to amp up my defenses a bit? It is disheartening to wait four years for a tree to produce only to have two crops in a row damaged. I also have pluots and plumcots but they havent started producing yet and I am afraid when they do, I will have the same problem.

Help!

Thank you,
Joy

Honestly, mix a teaspoon of liquid soap with a gallon of water to act as an emulsifier for the neem mixture and spray.

That should do the job for you, no need to mix in anything else.