Study on Venturia inaequalis pseudothecia development, ascospore discharge and prediction of Apple scab

Studies conducted on five apple cultivars during 2005-2008 showed that the highest number of Venturia inaequalis pseudothecia, ranging from 40 to 50 per l cm(2) of leaf surface occurred on 'McIntosh' and 'Cortland', while on 'Jonagold' and 'Idared' significantly lower number was observed. Usually ascospores matured the earliest on 'McIntosh' and 'Alwa' leaves. The calculation Of Cumulative degree-days index appeared to be unsuitable for forecasting of ascospore discharges. The evaluation of Italian A-scab model by using the archival data representing epidemiological and meteorological conditions in Central Poland (2005-2007) gave satisfactory results for simulated proportion of airborne ascospores in comparison to registered ascospores in orchard conditions. However, it is supposed that first predicted infections did not occur, because the first scab symptoms were related to later infections.