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Powdery mildew, caused by the fungus Sphaerotheca pannosa, appears in late spring or early summer as white mildew spots on the fruit (Fig. 1) and foliage. Later the spots on the fruit turn a tan colour. When severe, it may crack the fruit.
Figure 1. Nectarine infected with powdery mildew fungus.
Provide good air circulation through trees.
Cling peaches, nectarines and seedling peaches are especially susceptible and can serve as a source of infection.
Wild and cultivated roses can be a source of infection for powdery mildew on peaches and nectarines. They are affected by the same species of powdery mildew.
In some areas apple powdery mildew (Podosphaera leucotricha) can also cause injury to peach and nectarine fruit. This appears as rusty spots. Avoid locating peach or nectarine blocks next to highly susceptible apple varieties.
A fungicide applied at husk fall and during early fruit development will prevent powdery mildew damage to most peach and nectarine fruit. On very susceptible varieties provide coverage from full bloom to pit hardening.
Fungicides registered for control or suppression of powdery mildew on peach include:
Updated July, 2018