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Managing Phytophthora root rot on flood stressed woody ornamental plants

Fulya Baysal-Gurel: Tennessee State University

<div><em>Phytophthora cinnamomi</em> is an oomycete pathogen that attacks woody ornamentals; especially plants exposed to elevated soil moisture levels. During flooding events, Phytophthora root rot often causes damage in nurseries throughout the Southern and Eastern United States, sometimes leading to complete nursery crop loss. In this study, we evaluated the efficacy of fungicides and biofungicides for preventive and curative control of Phytophthora root rot on flooded dogwood seedlings. Fungicides/biofungicides were applied as preventive or curative drench treatments 7 d pre-flooding or 1 d post-flooding, respectively, to artificially inoculated dogwood, <em>Cornus florida</em>, seedlings. The plants were flooded by maintaining standing water for 1, 3, or 7 d, with five replications per treatment. After the experiment, plant growth data (fresh weight, root weight, plant height, plant width) were recorded, and roots were assessed for disease severity using a scale of 0-100% roots affected. Preventive treatments that reduced disease severity compared to a non-treated control included Subdue MAXX at 1, 3 and 7 d flooding and Orkestra Intrinsic at 1 and 3 d. Compared to the non-treated control, curative applications of Empress Intrinsic and Orkestra Intrinsic reduced disease severity at 1 and 3 d flooding. Fungicides/biofungicides can be incorporated into an integrated strategy to manage Phytophthora root rot on flood stressed nursery trees.</div>