Ayer, Katrin2021-12-202021-12-202021-08Ayer_cornellgrad_0058F_12636http://dissertations.umi.com/cornellgrad:12636https://hdl.handle.net/1813/110501143 pagesApples are an important specialty crop in New York State, and NYS is the second largest producers of apple nationwide. Of economic importance is the impact of managing the fungal pathogen causing apple scab, Venturia inaequalis. If left unmanaged, this disease will render the fruit unmarketable due to the malformation and commercially unacceptable olive-green to brown lesions that develop on fruit. The disease can also have negative impacts on overall tree health by reducing photosynthesis when the severity of leaf infection is high. In the absence of durable host resistance, commercial management relies heavily on the use of fungicides to prevent and control apple scab infections. Misuse of fungicides targeting a single site within fungi has resulted in sequential development of resistance to many classes of fungicide, resulting in ineffective fungal disease management. The first goal of this research was to characterize the efficacy and target site of succinate dehydrogenase inhibitors (SDHIs), a class of fungicides in which new chemistries have been released. This work demonstrated high in vitro efficacy of SDHI fungicides and provided the framework for future phenotypic and genotypic screening for fungicide resistance. The second goal of this research was to improve our understanding of how to best use these fungicides to prevent resistance development. We investigated practices involving application at both low and high doses as well as uses in different mixtures. We found that application at the higher doses often led to isolates with sensitivity shifted towards resistance. Additionally, this work reiterated the importance of mixing fungicide modes of action to prevent selection for resistance. Finally, the third goal of this research was to create a management plan that uses SDHIs with more sustainable biopesticide chemistries. We found potential for a program where SDHIs rotated with biopesticides could provide season-long management of apple scab. The work completed in this dissertation will help contribute to sustainable use of SDHI fungicides for the management of apple scab.enApple scabfungicide resistancesuccinate dehydrogenase inhibitorsdissertation or thesishttps://doi.org/10.7298/d1eh-z616