Fungicide sprays during the window of germination. A special tool for control of apple scab in organic and integrated apple production

Abstract: The most frequent factors responsible for failures in controlling apple scab (Venturia inaequalis) are the amount of fungal inoculum, poor strategy and timing of fungicide spray applications and the intrinsic, incomplete efficacy of the fungicides. Despite the progress made in apple scab control fungicides remain a highly underestimated risk because their less than 100% efficacy in the field is not gradable enough to match the enormous variation of inoculum, resulting in a high risk of poor control as the inoculum increases. The application of more than one fungicide spray per infection period is the only effective way of adapting the efficacy of scab control to high inoculum levels. A protectant is applied shortly before rain and a curative compound after the rain event if a severe infection has built up. The curative compound controls the spores which passed the protectant fungicide resulting in a significant increase of efficacy compared to just the protectant before the rain. When curatives are not available, a protectant may be applied during the window of germination, a time period when the ascospore relaease of the day has almost terminated but no, or just a few, spores have infected. The time window is determined using the simulation software RIMpro in conjunction with the weather forecast. This method has been introduced in organic fruit production (OFP) at Lake Constance area in 2002 and has improved the results of primary scab control to, or above, the level obtained in IFP. After having become standard in OFP, the method is also used in IFP after the detection of wide spread resistance to Anilinopyrimidines at Lake Constance area in 2005.