Epidemiological research on the etiology of twig scab as basis for a rationaland ecological disease management

Abstract: Scab is one of the key parasites in pome fruit. In favourable weather conditions, acomplete harvest can be destroyed if no control measurements are undertaken. The disease iscaused by the ascomycete Venturia inaequalis and V. pirina on apple and pear, respectively.Although they are two distinct species, their biological cycle is mainly the same. Two distinctionscan be made, i.e. the appearance of twig scab and the more important contribution of secondaryscab infections on pears. Especially in organic fruit growing, twig scab is a big problem. Untilnow, most research concerning scab disease is performed on apples and as such, the diseasemanagement of pear scab is based on that of apple. Based on the two discrepancies in theirbiological cycle, we believe that the timing of the fungicides to control pear scab can be betterpositioned and that less fungicide sprayings may be needed to control pear scab. For that reasonan IWT (Agency for Innovation by Science and Technology)-funded research project was startedto study pear scab in more detail. In this project the etiology and the importance of twig scab inthe epidemiological cycle of pear scab and its contribution to scab infections is investigated.Furthermore, the diversity of V. pirina biotypes and their pathogenicity on different plant parts orcultivars will be determined. The first results indicate that twig scab may be an important factorin the biological cycle of pear scab and that plant part or type of cultivar do not set up a barrierfor cross infections with scab conidia.