You want to spray from shuck split (not long after petal fall) until they are dime-sized. Sometimes you get strikes even later.
You also would need to pick off / pick up all those damaged fruits, part of the problem is you probably have a massive army of curcs from all the curc breeding your nectarine has been doing. Even Surround will not help against thousands of curcs on one tree.
There are many poisons that can be used to kill them, I don’t use it though so am not particularly knowledgeable. See Alan’s s schedule for example: