The role of the apple spray programme in the protection of fruit buds from powdery mildew

SUMMARY Comparisons of programmes, which differed in the dates on which high‐volume sprays of dinocap (0.019 %) were omitted, indicated that applications in the period from green cluster to early fruitlet protected the bourse buds of apple cv. Cox's Orange Pippin from infection, and so controlled the number of mildewed blossom trusses in the following year. This role of the sprays in preventing primary mildew declined after the early fruitlet stage. The existence of two phases of the disease was confirmed, and although dinocap at late blossom and early fruitlet contributed to the control of preliminary infections of secondary mildew on vegetative shoots, the latter phase did not become severe until after the peak invasion of bourse buds. Fewer than 20% of the fruit buds which produced primary‐mildewed blossom in 1968 were succeeded by healthy fruit buds in the next year; this poor recovery was not improved by dinocap applied during the flowering period in 1968. Fruit‐set and crop of James Grieve and Cox's Orange Pippin were reduced in 1968 by dinocap applied at green cluster and pink bud, or at full blossom and petal‐fall, but no deleterious effects were produced by equivalent sprays in 1969. The need for mildew control during flowering is discussed in relation to phytotoxic sensitivity.