The influence of moisture, light, and temperature on Venturia pirina ascospore maturation and discharge was studied during 1992-99 in 2 pear-growing regions in Victoria. In each year and site, mature ascospores were trapped over a 3-month period beginning a few days before or at the green-tip stage of pear tree development in early September and ending in late November, with the majority of ascospores ((>80%) trapped between green-tip and petal-fall. Ascospore discharge was associated with rain and dew, with 90-98% of the season 's total number of ascospores trapped during rain events and 2-10% trapped during dew events in the 12 data sets examined. Most ascospores were trapped (82.5- 99.9%) during daytime (0600-1800 hours). The 0.1-17.5% of ascospores detected during night time (1900-0500 hours) were trapped mainly within 1-3 h of dawn or dusk. There were linear relationships between the logit of cumulative percentage of ascospore maturation and temperature accumulation (above 0 degree-days), calculated both daily and for days with >= 0.2 mm of rainfall. Six linear regression equations were formulated with 10 years of field data and using the 2 methods of accumulating degree-days, to predict the cumulative percentage of matured ascospores. Predictions were compared with additional field and laboratory observations not used in the formulation of the linear equations. The importance of the temperature-based linear equations is discussed in relation to the prediction of pear scab ascospore maturity for use in a pear scab management program.