Do I need to dormant spray my peach tree for leaf curl every year?
When peach leaf curl is extensive, fruiting wood renewal and productivity for peach and nectarine trees can be substantially diminished. An annual dormant fungicide spray may give sufficient control, but in areas where leaf curl pressure is especially high, two sprays of a fixed copper product are commonly recommended: in fall as soon as most leaves are off the tree and again just before bud break in early spring. For the worst instances, an additional spray in midwinter may be necessary. Be aware that copper in the soil can build up over many years, eventually becoming toxic to soil organisms.
Note that the incidence of peach leaf curl can vary markedly from year to year, depending on temperatures and number of rainy days during the early weeks of growth in spring. Also, though almost all peach and nectarine varieties are susceptible to curl, the degree of susceptibility varies.
See also the question "How can I keep my fruit trees free of pests and disease?"