Looks like armored scale to me. I don't know if chemical sprays would be effective against their waxy outer coating. A systemic would do the trick, but you can't eat the fruit from this year, or possibly longer. Always follow the directions on the label.
I've never dealt with them, but I know they can be tricky to get rid of. Good luck.

If your tree isn't too large, you can scrape them off by lightly rubbing with a rough kitchen scrubber. Google armored scale for other remedies, such as horticultural oil, to help keep them under control.

Elaine