Influence of infection parameters on pear scab dynamics in organic orchards in the Netherlands, 2010-2013.

Pear scab remains an important pest for organic pear production in The Netherlands. The disease incidence over the years shows a quite irregular pattern: for farmers in some years infection incidence seems to increase suddenly, whereas in other years incidence is rather low. In this project we tried to understand disease dynamics and quantify and influence various infections parameters. In order to do this, we measured a number of infection related parameters in 8 organic orchards throughout the Netherlands from 2010 to 2013: amounts of leaf litter, ascospore production per unit of leaf litter, twig scab incidence (only 2012) and scab incidence. The results show large, perennial and robust differences in leaf litter amounts between orchards. Furthermore, the amount of ascospores per unit of leaf litter show a nonlinear relation with scab incidence the previous year, suggesting a threshold value above which spore density increases. Twig lesion numbers support this relation. We use this nonlinear relation, combined with various infection parameters, as a basis to understand (part of the) disease dynamics