Development of a pre budbreak climate model to forecast the onsetof Venturia inaequalis ascospore ejection

Abstract: Most apple scab fungicides target primary infections caused by ascospores ejectedduring rain events. Because ascospore maturation is not always synchronous with hostphenology, ascospore release models may require adjustment at bud break when ascosporesmature early, or when maturation is delayed. In seasons with early ejection patterns, the scab riskof early infections can be underestimated. Conversely, sprays applied too early during seasons oflate ejection patterns are not useful. Weather conditions during late winter are known to impactboth ascospore maturation and spore production (Philion et al., 2008, 2009). The purpose of ourproject was to model shifts in the distribution of ascospore release based on weather, and proposea method to adjust the biofix for the onset of ejection.