Species Differ in Response to Phosphorous Acid and Mefenoxam for the Management of Phytophthora Root Rot in Rhododendron.

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ID: 263841
2020
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Abstract
Phytophthora root rot, caused by many soilborne species, is a significant disease affecting the $42 million rhododendron nursery industry. Rhododendron growers have increasingly reported failure by two systemic fungicides, phosphorous acid and mefenoxam, to adequately control root rot. Both fungicides may be applied as a foliar spray or soil drench, but it is unknown how application method, fungicide chemistry, or pathogen diversity affects disease control. Therefore, two experiments were conducted to (i) determine whether differences in application method or fungicide chemistry affect control of root rot caused by and and (ii) evaluate the sensitivity of species and isolates from the rhododendron industry to each fungicide. Results demonstrated that soil drenches of either fungicide were more effective than foliar sprays for control of , but were ineffective for . Furthermore, species and isolates varied in sensitivity to phosphorous acid and mefenoxam, and there were multiple fungicide insensitive isolates, especially within . Differences in sensitivity were also observed among isolates from different nurseries and production systems, with some nurseries having less sensitive isolates than others and with container systems generally having less sensitive isolates than field systems. Our results provide three potential reasons for why fungicide control of Phytophthora root rot might fail: (i) the fungicide can be applied to the wrong portion of the plant for optimal control, (ii) there are differences in fungicide sensitivity among soilborne species and isolates infecting rhododendron, and (iii) fungicide insensitive isolates are present in the rhododendron nursery industry.
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weiland2020plant Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Weiland, Jerry E;Scagel, Carolyn F;Grünwald, Niklaus J;Davis, E Anne;Beck, Bryan R;
Journal Plant disease
Year 2020
DOI 10.1094/PDIS-09-20-1960-RE
URL
Keywords
chemical disease management oomycetes pathogen diversity causal agent subject areas crop type ornamentals phytophthora cinnamomi phytophthora plurivora mefenoxam phosphite phosphonate rhododendron woody ornamentals

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