Apple russetting influenced by more than copper sprays

Apple trees are commonly treated with antibiotics during bloom and early shoot growth to control fire-blight, but antibiotic resistance is a concern. To prevent antibiotic resistance, copper treatments may be beneficial, but would be feasible only if stages in bloom or fruit development could be identified that are not subject to fruit russetting. Most fruit russetting results from injury to epidermal cells early in fruit development. Studies in Kern and San Joaquin counties showed copper-induced russetting of apple fruit was unpredictable and sporadic regardless of application timing. Severity of damage varied from year to year.