There are a number of dormant sprays (available at garden centers) used on fruit to control various diseases and insects, but a dormant oil spray is designed to control scale insects. If you have a problem with scale, now is the time to start looking for an opportunity to spray. Normally a dormant oil spray should be applied by March 1, especially with peaches and nectarines.
Apples are tougher, and application may be delayed up to the green tip stage. Temperatures need to be at least 40 degrees so spray has a chance to dry before freezing. If the spray does freeze before it dries, plant injury can occur. Applying the spray during the morning will help insure that it dries properly. Thorough coverage of limbs, branches, and twigs is vital for good control. Note that it is much easier to achieve good spray coverage if the tree is pruned before spraying.