Institute of Entomology and Plant Pathology, “S. Cuore” Catholic University, Via E. Parmense 84 29100 Piacenza, Italy
The effect of weather conditions on the infection of peach shoots by Taphrina deformans was investigated both under orchard conditions and in controlled-environment experiments. Leaf curl incidence and severity were related to rainfall, length of wet periods, and temperature during wetness and during the incubation period, as well as to the development stage of shoots. Surface wetness was more important than rainfall for infection to occur. Minimum rainfall for infection was 3 mm, with a wet period of at least 12.5 h; higher amounts of rainfall did not cause infection when the wet period they triggered was shorter. Wet periods initiated by dew or fog were too short for infection to occur. Infection occurred only when air temperature was <16°C during the wet period and <19°C during incubation. Logistic equations relating relative disease incidence and either duration of wetness or temperature were developed under controlled-environment conditions, with asymptotes at ≥48 h of wetness and ≤8°C for temperature, respectively. Rate of shoot and leaf development during the season influenced disease development, so that three different periods of susceptibility were defined, maximum susceptibility being between bud break and petal fall due to a low development rate of shoots.