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Madhav Parajuli and Fulya Baysal-Gurel

Phytophthora nicotianae and Rhizoctonia solani are the well-described soilborne pathogens of concern causing Phytophthora and Rhizoctonia root rot, respectively, of red maple plants (Acer rubrum L.), resulting in substantial economic losses to nursery growers. The management of root and crown rot disease of red maple is a big challenge. The objective of this study was to test the efficacy of several fungicide and biofungicide products to control Phytophthora and Rhizoctonia root rot on red maple plants in greenhouse conditions. Treatments, including fungicides and biofungicides, and nontreated and inoculated and nontreated and noninoculated as controls were arranged in a completely randomized design with six replications. Red maples planted in number 1 nursery containers were artificially inoculated with P. nicotianae or R. solani. Plant height, plant width, total fresh weight, and root fresh weight were measured and roots were assessed for root rot disease severity based on a scale of 0% to 100% root damaged. The pathogen recovery percentage of plant roots was determined by culturing ten randomly selected root pieces (≈1 cm long) cut from the root tips on Phytophthora selective medium (PARPH-V8) or Rhizoctonia semi-selective medium. All tested fungicides and biofungicides reduced Phytophthora and Rhizoctonia root rot on red maple plants compared with the nontreated and inoculated control. Likewise, pathogen recovery was lower for fungicide-treated and biofungicide-treated plants. Fungicides, such as mefenoxam, oxathiapiprolin, pyraclostrobin plus boscalid, and pyraclostrobin provided the most effective control of Phytophthora root rot. Pyraclostrobin plus boscalid and pyraclostrobin followed by biofungicides Bacillus amyloliquefaciens strain F727 and Trichoderma harzianum Rifai strain T-22 plus T. virens strain G-41 were most effective for suppressing Rhizoctonia root rot. There were no differences in plant height, plant width, plant fresh weight, and root fresh weight among the treatments. These findings will help nursery producers make decisions while formulating soilborne disease management strategies for red maple production.