Efficacy of fungicide treatments against cucurbit powdery mildew in the greenhouse in Knoxville, Tennessee, 2022-23

Authors: COUNCE, ALYSSA - University Of Tennessee; GWINN, KIMBERLY - University Of Tennessee; WANG, TONI - University Of Tennessee; Hansen, Zachariah

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2025
Publication Date: 6/18/2025
Citation: Counce, A., Gwinn, K., Wang, T., Hansen, Z.R. 2025. Efficacy of fungicide treatments against cucurbit powdery mildew in the greenhouse in Knoxville, Tennessee, 2022-23. Plant Health Progress. https://doi.org/10.1094/PHP-02-25-0046-PDMR.
DOI: https://doi.org/10.1094/PHP-02-25-0046-PDMR

Interpretive Summary: Cucurbit powdery mildew, caused by the fungus Podosphaera xanthii, is an important disease of cucurbits such as melons and squash, especially in greenhouse environments. Powdery mildew symptoms include white, powdery fungal growth on above-ground plant parts including leaves, stems, and petioles. Powdery mildew causes blighting of leaves, resulting in reduced yield and quality. This report evaluates the efficacy of eight fungicides, including commercial and experimental products, for managing powdery mildew on acorn squash (Cucurbita pepo ‘Table Queen’) in a greenhouse in Knoxville, TN in November 2022 and February 2023. Most fungicides, including experimental products, managed powdery mildew well compared to non-treated controls, indicating there are a variety of options available for powdery mildew management in commercial greenhouse cucurbit production. This work provides valuable information for greenhouse cucurbit growers to help manage this challenging disease.

Technical Abstract: Cucurbit powdery mildew, caused by the fungus Podosphaera xanthii, is an important disease of cucurbits, especially in greenhouse environments. Powdery mildew symptoms include white, powdery fungal growth on above-ground plant parts including leaves, stems, and petioles. Powdery mildew causes premature leaf senescence, resulting in reduced yield and quality. This report evaluates the efficacy of eight fungicides, including commercial and experimental products, for managing powdery mildew on acorn squash (Cucurbita pepo ‘Table Queen’) in a greenhouse in Knoxville, TN in November 2022 and February 2023. Most fungicides, including experimental products, managed powdery mildew well compared to non-treated controls, indicating there are a variety of options available for powdery mildew management in commercial greenhouse cucurbit production.