Improving the implementation of disease forecasting systems and an alternative management program to mitigate regulatory concerns with multi-site fungicides for apple scab management

Apple scab, caused by Venturia inaequalis, requires regular fungicide applications to achieve adequate disease control. Multi-site fungicides such as mancozeb and captan are integral to chemical management programs due to resistance concerns. To reduce reliance and mitigate regulatory concerns with multi-site fungicides, there has been increased demand for more sustainable solutions. We attempted to use disease forecasting to enhance potential for alternative programs replacing multi-site fungicides with biopesticides to manage apple scab in plantings of cvs. Jonagold and Empire apples. Programs included: untreated control, ‘grower-standard’ program of conventional multi-site fungicides alternated with single-site fungicides on a calendar schedule, a program where biopesticides alternated (in place of multi-sites) with single-sites on calendar schedule, several programs where biopesticide alternated (in place of multi-sites) with single-sites timed using one of three different disease forecasting tools (NEWA, RIMpro, or Weather services). Programs were carried out for standard and extended season management trials. Disease incidence on terminal leaves and fruit was rated at the end of the season; mean incidence was calculated and analyzed. In all years of the study on ‘Jonagold’ apples, we observed no significant differences (P > 0.05) among management programs suggesting that integrated programs would be viable and that any forecasting-based timing used in our study can be just as effective as a calendar schedule. For the cv. ‘Empire’ apples, which are more susceptible to apple scab, the extended season program with NEWA based applications provided the best control. Despite the promising results using biopesticides instead of multi-site fungicides, we can’t be certain whether the multi-sites fungicides or biopesticides were effective rotational partners are simply not needed without additional studies without additional controls. Regardless, something is needed to provide a modicum of coverage and ensure fungicide resistance management during low-risk periods, and biopesticides are one of the more environmentally responsible means. However, our results provide a cultivar dependent framework for developing management programs without multi-site fungicides using disease forecasting, while achieving better disease control and ensuring fresh market yields.