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Influence of Weather Conditions on Infection of Peach Fruit by Taphrina deformans

The effect of environment on the infection of peach fruit by Taphrina deformans was investigated using orchard observations under natural conditions (in 2001 to 2004) or in trees managed in such a way to exclude rainfall. These conditions were then validated using pot-grown peach plants exposed to single infection events and independent orchard observations. Leaf curl incidence was related to rainfall, length of wet periods, and the temperature during wetness and during the incubation period, as well as to the developmental stage of flowers and fruit. Weather conditions before petal fall did not influence fruit infection. After petal fall, rainfall and the duration of the wet period triggered by rainfall played a key role in infection occurrence. The minimum rainfall required for infection was 12 mm, with at least 24 h of wetness interrupted by no more than 4 h. No infection occurred when temperature was ≥17°C during the wet period or >19°C during incubation. Disease symptoms appeared on fruit after approximately 3 weeks of incubation, which is equivalent to 240- to 290-degree-days (base 0°C). The period for fruit infection was relatively short being from petal fall until air temperature remained greater than 16°C. During this period, the incidence of fruit that developed symptoms was closely related to the number of favorable events and the total wetness duration during such events.