Nectarines are fuzzless peaches. The fuzz on peach fruit offer natural protection from some small insects that attack the fruit like the flower thrips. Flower thrips are out very early attacking anything soft and fleshy they can get their ripping and shredding mouthparts on. Those mouthparts slash away at soft tissue like flowers, emerging leaves and the like as soon as they emerge. I have seen flower thrip damage on the ovary of a nectarine flower while the flower was still open and not yet pollinated. They are nasty.
Pictures of thrips
I have had reports from people this year already about rose flowers not opening or the petals looking "water-soaked" and damaged before the flower opens. That's what flower thrips will do. That is natural for them.
There are conventional insect sprays that can be used against flower thrips with some success but the sprays must be repeated. Check for sprays labeled for fruits.
Botanical and organic sprays will include soap sprays, Spinosad, pyrethrins and oils. Use them in a sequential rotation (one followed by a different one, followed by a different one) when spraying, use a spreader sticker and focus the spray to cover the fruit. This is one reason why you should not skip winter applications of dormant oils on plants that get hit by flower thrips.