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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #412518
Research Project: Knowledge Based Tools for Exotic and Emerging Diseases of Small Fruit and Nursery Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Evaluation of germicidal UV-C light for suppression of grape powdery mildew and Botrytis bunch rot in Western Oregon

Author
item WONG, ALEX - Oregon State University
item GADOURY, DAVID - Cornell University
item Mahaffee, Walter - Walt

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Growers are faced with increasing market pressure to reduce fungicide use while increasing product quality (e.g., disease free fruit). In addition, fungicide resistance is becoming more common against the most cost effective fungicides. Producers need alternative tools for disease management and germicidal ultraviolet light could be suitable. This research examined the effectiveness of UV-C (256 nm) light applications for management of grape powdery mildew and botrytis bunch rot. Results demonstrate that there is utility for mildew management but that its application is not cost effective currently and that further research on dose, wavelength, and method of application is needed.

Technical Abstract: Germicidal ultraviolet light (UV-C) has been shown to effectively suppress several plant pathogens, as well as some arthropod pests. Recent reports describe the efficacy of nighttime applications of UV-C at doses from 100 to 200 J/m2 in vineyards to reduce grape powdery mildew (Erysiphe necator). Our in vitro studies confirmed efficacy of UV-C to inhibit germination of E. necator and Botrytis cinerea conidia, demonstrated a range of tolerances to UV-C within a collection of E. necator isolates, and showed growth stage-specific effects of UV-C on B. cinerea. Nighttime use of UV-C was evaluated at doses of 48 to 96 J/m2 in small plot trials (<1,000 vines) from 2020 to 2023, and once or twice 27 weekly UV-C applications significantly reduced the incidence of foliar powdery mildew compared to non-UV-C-treated controls (P < 0.02). Suppression of powdery mildew on fruit was less consistent, where once or twice weekly UV-C exposure reduced powdery mildew disease severity in 2020 (P = 0.04), 2021 (P = 0.02) and 2023 (P =0.003), but less so in 2022 (P = 0.07). Application of UV-C until the onset of fruit color change (veraison) also had a minimal effect on the fruit soluble solids, pH, anthocyanins, or phenolics in harvested fruit at any UV-C dose or frequency (P > 0.10). Suppression of powdery mildew by nighttime application UV-C at lower doses in small plots suggests that such treatments merit further evaluation in larger-scale studies in Western Oregon.