Ambrosia beetles (Coleoptera: Curculionidae, Scolytinae) and Phytophthora root rot (Peronosporales: Peronosporaceae) cause significant damage to the ornamental industry in the United States. In this study, mefenoxam (fungicide), permethrin (insecticide), and charcoal + kaolin were used in different combinations with Phytophthora cinnamomi (Rands: Peronosporales: Peronosporaceae) inoculated and noninoculated plants to optimize the management of ambrosia beetles and Phytophthora root rot. Treatment applications were performed in two trials on 1 (mefenoxam, drench), 18 (P. cinnamomi inoculation), or 19 (permethrin, spray) days before instigating flood stress or 2 d after flood stress (charcoal + kaolin, spray), respectively. Flooding was maintained for 21 d. Ambrosia beetle attacks and plant growth data were recorded. Tree roots were rated at study end for disease severity and root samples were plated on PARPH-V8 medium to determine the percentage of pathogen recovery. In both trials, the combination of mefenoxam + permethrin treatment had reduced disease severity and ambrosia beetle attacks compared to the inoculated controls. Permethrin-treated trees had shorter galleries compared to controls in trial 1 and no gallery formation in trial 2. In both trials, no differences were observed among the treatments in numbers of galleries with eggs and adults, but mefenoxam + charcoal + kaolin had significantly fewer galleries with larvae among the noninoculated trees compared with the respective control in trial 1. Overall, treatments containing combinations of mefenoxam + permethrin had reduced disease severity and ambrosia beetle attacks.
Keywords: Coleoptera; Scolytinae; fungicide; insecticide; oomycete.
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