Improving the Implementation of Disease Forecasting Systems and an Alternative Management Program to Mitigate...

Apple scab, caused by Venturia inaequalis, requires regular fungicide applications to achieve adequate disease control. Multisite fungicides such as mancozeb and captan are integral to chemical management programs because of resistance concerns. To reduce reliance and mitigate regulatory concerns with multisite fungicides, there has been increased demand for more sustainable solutions. We attempted to use disease forecasting to enhance potential for alternative programs replacing multisite fungicides with biopesticides to manage apple scab in plantings of cvs. 'Jonagold' and 'Empire' apples. Programs included untreated control, "grower-standard" program of conventional multisite fungicides alternated with single-site fungicides on a calendar schedule, a program in which biopesticides alternated (in place of multisites) with single-sites on calendar schedule, several programs in which biopesticide alternated (in place of multisites) with single-sites timed using one of three different disease forecasting tools (Network for Environment and Weather Application [NEWA], Relative Infection Measure program [RIMpro], or U.S. National Weather Service). 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 '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 multisite fungicides, we cannot be certain whether the multisite fungicides or biopesticides were effective rotational partners or are simply not needed, without additional studies and 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 multisite fungicides using disease forecasting, while achieving better disease control and ensuring fresh market yields.