A new apple scab risk model that integrates ascospore release infection risk and susceptible leaf area

Abstract

A new model has been developed for assessing daytoday variation in risk of infection of apples by Venturia inaequalis the scab or black spot pathogen The model comprises three components ascospore availability wetnessbased infection risk based on Mills periods and susceptible leaf area The ascospore and wetnessbased infection risk components were adapted from previous models whereas the susceptible leaf area component is new When the model used weather data from Hawkes Bay and Nelson in spring 2003 the predicted risk incidence was determined mostly by wetnessbased infection risk but the magnitude of risk periods was greatly influenced by predicted ascospore release The susceptible leaf area component predicted a hitherto unidentified increase in infection risk after the peak in ascospore maturation rate had occurred The model is intended to assist in fungicide selection and timing for scab control in New Zealand apples but needs to be field tested before implementation