Effect of Temperature and Wetness on Infection of Pear by Venturia pirina and the Relationship Between Preharvest Inoculation and Storage Scab. R. A. Spotts, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, Hood River 97031. L. A. Cervantes, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, Hood River 97031. Plant Dis. 75:1204-1207. Accepted for publication 16 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1204.

The effects of conidial inoculum dose and selected combinations of temperature and wetness duration on the incidence and severity of pear scab on fruit and foliage were studied. The relationship between the time of preharvest infection of pear fruit and the length of storage at –1 C before symptoms developed also was determined. Incidence and severity of scab on leaves and shoots of Bartlett pear seedlings increased linearly as inoculum concentration increased from 5 × 10² to 5 × 10⁴ conidia per milliliter. Minimum wetness duration for foliar infection varied from 10 hr at 23.9 C to 25 hr at 7.2 C and was similar to apple scab infection periods determined by Mills. Fruit infection was minimal at 7.2 and 10 C but increased to more than 20% at 15.5 C for 15 hr of wetness and 21.1 C for 14 hr of wetness. Anjou and Bartlett fruit inoculated within 2 wk before harvest developed symptoms in storage at –1 C after 2–6.5 mo, but inoculation 4 wk before harvest required less than 2 mo of incubation. These relationships were described with second-order polynomial regression equations. Dodine application 1 day before or after preharvest fruit inoculation gave good control of scab in cold storage.

Keyword(s): Pyrus communis.