If they are about to break bud it may be too late, but if you want to try, you need to do it immediately.

Carla in Sac

I would spray with copper, asap. Mrs. G

thanks guys, this helps lots. I managed to talk to the guy at the nursery and he says they have been sprayed 3x but need one more at valentines day.

Princess Pea:

Peach leaf curl is caused by a fungus (Taphrina deformans).
The fungus overwinters on buds, bark ect. When the bud scales swell and crack in spring, the fungus attacks the meristem. The leaves will open up twisted/puckered and have pink or yellow lumps on them. Once you see this, you will never forget this disease.

To prevent, you must spray with a fungicide BEFORE the leaf
buds crack open. It is too late to spray afterwards and get control. I spray with chlorothalonil in late March and
again a second spray the first week in April for SE WI. Your area is different than mine so all I can say is that you need to spray while the tree is dormant and be sure to
cover the entire tree (trunk, branches ect).

I cannot comment on "resistant" peach varieties as I have no experience with them.