Factors Affecting Release of Ascospores by the Pear Scab Fungus (Venturia pirina). B. A. Latorre, Adjunct Professor, Departamento de Ciencias Vegetales, Facultad de Agronomía, Pontificia Universidad Católica de Chile, Casilla 6177, Santiago, Chile. P. Yañez, and E. Rauld, Former Students, Departamento de Ciencias Vegetales, Facultad de Agronomía, Pontificia Universidad Católica de Chile, Casilla 6177, Santiago, Chile. Plant Dis. 69:213-216. Accepted for publication 26 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-213.

Ascospores of Venturia pirina were monitored under field conditions in 1982 and 1983 with a Burkard 7-day recording spore trap adjusted to sample about 8 m³ of air per hour at 55 cm above the ground. Ascospore productivity was determined weekly by sampling partially decomposed pear leaves near the spore trap. Ascospore emissions occurred mainly during daylight hours and fluctuated daily and seasonally (associated with periods of free moisture). The first mature ascospores were found when pear trees were in the green tip stage of fruit bud development (late August and early September). Maximum ascospore catches were recorded in September (white cluster to full bloom stage of fruit bud development), then progressively decreased until December. The lack of later liberation under Chilean conditions is apparently due to the absence of free moisture periods.