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Phytophthora root rot causes major economic losses in woody ornamental nurseries, especially in plants exposed to flooding. Ambrosia beetles, which attack stressed trees, are also important pests of woody plants. In this study, several products were evaluated for control of Phytophthora root rot and ambrosia beetles on containerized flowering dogwoods (Cornus florida L.) exposed to simulated flood events under field conditions. In two trials, preventive (7 days preflooding) or curative (1 day postflooding) sprench (combination spray and drench) treatments were applied to containerized dogwoods artificially inoculated with Phytophthora cinnamomi Rands. The plants were flooded by maintaining standing water for 1, 3, or 7 days. After the trials, plant growth data (dry shoot weight, dry root weight, plant height, plant width, caliper) were recorded, and roots were assessed for disease severity using a scale of 0–100% roots affected, as well as plated on PARPH-V8 medium to determine the percentage of Phytophthora-infected root samples. Ambrosia beetle attacks were recorded throughout the study. Longer flooding duration increased disease pressure from Phytophthora cinnamomi Rands. Preventive treatment of plants with Subdue MAXX consistently reduced disease severity at tested flooding durations of 1, 3, or 7 days. Preventively- (before flooding) or curatively- (after flooding) applied treatments of Empress Intrinsic, Orkestra Intrinsic, and Pageant Intrinsic reduced disease pressure at 1 and 3 days of flooding. Preventive RootShield Plus+ treatment reduced disease pressure on plants flooded 1 day. Longer flooding periods as well as Phytophthora cinnamomi inoculation increased ambrosia beetle attacks on flooded dogwoods, but preventively- and curatively-applied Orkestra Intrinsic as well as preventively-applied Subdue MAXX reduced ambrosia beetle attacks compared to non-treated, inoculated controls. These treatments were effective at reducing both Phytophthora and ambrosia beetle damage. These results can help nursery producers successfully manage Phytophtora root rot and also reduce the risk of ambrosia beetle attacks during flood events.

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