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Phytophthora on annual vinca in greenhouses

Tue, May 9th, 2023, created by Jean Williams-Woodward

Phytophthora crown rot and foliar blight, caused by Phytophthora nicotianae, was recently seen on annual vinca (Catharanthus roseus) within greenhouse production. Infected plant symptoms ranged from wilted, greenish to brown individual stems of otherwise healthy-looking plants to completely dead transplants. Dark lesions often extended upward on the stem from the soil line, and roots were small and darkly discolored. Be on the lookout for early Phytophthora crown rot symptoms of wilting green plants. There is no cure for Phytophthora-infected plants in production. Infected plants should be discarded to reduce pathogen spread. Phytophthora infection is favored by wet, humid, warmer conditions, and it is spread by water-splashing. Management of this disease is best done preventively through fungicide drenches. Fungicides containing (listed alphabetically) azoxystrobin, cyazofamid, dimethomorph, fenamidone, fluopicolide, fosetyl-Al, mandipropamid, mefenoxam, oxathiapiprolin, phosphorous acid (phosphonates), and pyraclostrobin can reduce infection when used preventively and at 7- to 21-day intervals depending upon the product. Products need to be rotated with products with a different mode of action (different numerical code) to reduce fungicide resistance development. Resistance is known, particularly to mefenoxam. (Please note: The mention of specific active ingredients does not constitute an endorsement or recommendation of, nor discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.)

About the Author:

Jean Williams-Woodward

Associate Professor, University of Georgia

Jean is an Associate Professor and Extension Plant Pathologist at the University of Georgia. Jean provides statewide plant disease diagnosis and management recommendations for ornamental plants in greenhouses, nurseries, and landscapes. She also teaches courses in plant disease diagnosis and ornamental pest management. She brings over 27 years of experience in working with ornamental plant producers and extension outreach providing education programs and on-site plant problem diagnostics.

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