Abstract
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Three fruit rots of apples have been reported in the Midwest of the United States, which are bitter rot, black rot, and white rot caused by Colletotrichum spp., Botryosphaeria obtusa, and Botryosphaeria dothidea, respectively. In the past 10 years, outbreaks of bitter rot disease occurred in Illinois apple orchards. This study was conducted to develop effective management of fruit rots in Illinois. Orchard surveys conducted during 2019-2021 showed that 58, 67, and 64% of the orchards in 2019, 2020, and 2021, respectively, had from 0.7 to 100% of apple fruits with bitter rot symptoms. During the surveys, 270 isolates of Colletotrichum fungi were collected from the symptomatic fruits of ‘Braeburn’, ‘Cortland’, ‘Empire’, ‘Fuji’, ‘Gala’, ‘Golden Delicious’, ‘Gold Rush’, ‘Granny Smith’, ‘Honeycrisp’, ‘Jonagold’, ‘Jonathan’, ‘McIntosh’, ‘Red Delicious’, and an unknown cultivar of apples from 33 orchards. Pathogen species were identified based on the morphological and molecular characteristics of the isolates. GAPDH gene sequence analyses identified species of the pathogens as Colletotrichum fioriniae, C. siamense, and C. chrysophilum. Laboratory and orchards studies were conducted to evaluate effectiveness of fungicides for managing bitter rot disease. Laboratory studies showed 8.3, 8.0, and ≤0.11 mg/L EC50 of benzovindiflupyr, captan, and fluxapyroxad + pyraclostrobin fungicides, respectively. Orchard experiments were conducted in 2019, 2020, and 2021 on ‘Honeycrisp’ apple. Benzovindiflupyr (Aprovia 0.83SC), captan (Captan 80WDG), and fluxapyroxad + pyraclostrobin (Merivon 4.18S) prevented development of bitter rot and other fruit rots in the treated plots.
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