The best time to spray
Peaches and nectarines should actually be sprayed 3 times each winter to prevent peach-leaf curl. The first (and most important) time to spray is in fall when about half the leaves have fallen. We recommend a combination of a copper spray with a spreader sticker. The first spray should also include dormant spray oil to kill any insects hoping to over-winter. The key is to make this first application before winter storms and while there is still some foliage to absorb the spray.
The second application should be made at full dormancy in mid-winter.
The third and final application should be made during pink bud swell, but prior to opening of blooms.
(We recommend staying upwind from the spray unless you are planning to audition for the Blue Man Group.)