Integration of Biopesticides into Apple Scab Management Programs Using Disease Forecasting and Modern Planting Systems

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 due to resistance concerns. To reduce this reliance on multisite fungicides and mitigate regulatory concerns, there has been increased demand for more sustainable solutions. We attempted to integrate biopesticides into management programs with single-site fungicides using disease forecasting to better time applications. Disease incidence on terminal leaves and fruit was rated at the end of the season; mean incidence was calculated and analyzed. No significant differences (P > 0.05) were observed among management programs, suggesting that integrated programs would be viable and that forecasting-based timing can be just as effective as a calendar schedule. While the results seem promising, we cannot be certain whether the multisite fungicides or biopesticides were effective or were simply not needed without additional controls. Regardless, growers will want to apply something for fungicide resistance management and to maintain a modicum of coverage during low-risk infection periods. Of the options, biopesticides are one of the more environmentally responsible. Compared with the vertical axis planting, the super spindle planting had lower canopy relative humidity and fewer days where the relative humidity exceeded 90%. While we observed lower incidence of disease in the super spindle planting in years 2022 and 2023, this was not the case in 2024. Hence, the potential for successfully using biopesticides for apple scab may not be more easily accomplished by super spindle plantings. Given that we observed no significant differences (P > 0.5) in the incidence of apple scab symptoms of leaves and fruit between integrated and conventional programs during this 2-year study, it may be possible to achieve adequate disease control without the use of synthetic multisite fungicides when single-site fungicides are used optimally in rotation biopesticides.