A NEW MODEL ESTIMATING THE SEASONAL PATTERN OF AIRBORNE ASCOSPORES OF VENTURIA INAEQUALIS COOKE WINT IN RELATION TO WEATHER CONDITIONS
V. Rossi, M. Marinelli, I. Ponti, S. Giosuè1, R. Bugiani
A simple model estimating the seasonal pattern of air-borne ascospores of Venturia inaequalis was elaborated, by using spore trapping records collected during a 6-year period (1991-1996) in the Po Valley (North Italy). The model estimates the proportion of the season’s ascospores trapped by using weather factors which occur after the first appearance of mature ascospores inside the pseudothecia. Temperature and leaf wetness are the driving variables included in the model, expressed as degrees (above 0°C) accumulated daily in the hours when leaves are wet. The model is a non-linear regression that describes the relationship between degree-days and the proportion of the season’s ascospores, expressed as a mean and its confidence intervals. The model was verified by comparison with its component data sets, and was validated with additional observations of the ascospore trappings made in 1997 and 1998. Validations showed that the model makes accurate estimates, which could be used in the warning systems for apple scab management, instead of records from spore traps.