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Diagnosis and management of postharvest fruit rots of winter squash (Cucurbita maxima) in Oregon’s Willamette Valley

Hannah Rivedal: Department of Botany and Plant Pathology, Oregon State University

<div>Postharvest fungal rots reduce winter squash profitability in Oregon’s Willamette Valley. Commonly, desirable cultivars grown with overhead irrigation show 50-100% losses by December. Surveys of representative squash fruits in 2016 and 2017 characterized type and severity of postharvest fungal rots<em>. </em>Koch’s postulates experiments of novel fungi associated with fruit rots are being conducted. Identified fungi associated with postharvest rots include <em>Fusarium culmorum </em>- a pathogen commonly infecting grasses and some dicotyledonous hosts. We are hypothesizing that this fungus establishes a quiescent infection in fruits via infection of summer flowers. Floral infections may begin when <em>F. culmorum </em>spores in grass debris from previous crop rotations are splashed via overhead irrigation onto squash flowers. If this hypothesis is supported, a proposed management strategy is to grow winter squash under limited irrigation or dryland production. When grown with overhead irrigation, the desirable cultivar ‘Sunshine’ had up to 100% storage loss by January, compared to only 5% storage loss by March when produced under dryland conditions. Additional hypothesized management strategies to reduce irrigation splash include using vetch or brassica mulches that do not host <em>F. culmorum</em>. Field trials comparing dryland, irrigated, and mulched production strategies will be conducted to develop the most effective management strategy for postharvest fruit rots of winter squash.</div>