Efficacy of alternative substances to control apple scab by leaf litter treatment

Currently, a frequently used and effective strategy to control apple scab in organic fruit growing is the application of copper in combination with sulphur. With regard to the intended EU-wide prohibition of copper as a plant protectant, it is thus of the utmost importance to find comparable alternatives. This study therefore focuses on the decrease of the infection threat during spring by the reduction of sporulation from the leaf litter. This reduction is to be achieved by treatments of the leaf litter with substances, that potentially have a direct fungicidal effect on the apple scab pathogen itself or enhance microbial competition, and, secondly, show an indirect effect by increasing the attractiveness of the treated apple leaves for earthworms and consequently their decomposition. In addition to several plant extracts, two yeast extracts, a soya-containing medium and different individual components were tested. First results show, that casein-peptone, TSB (Tryptic Soy Broth) and casamino acids can reduce the ascospore potential by more than 90 % compared to the untreated control. Furthermore, the first experiments indicate, that one of the yeast extracts leads to an accelerated decomposition of the leaves by earthworms.