1. Baseline Sensitivities of New Fungicides and Their Toxicity to Selected Life Stages of Phytophthora Species from Citrus in California.
- Author
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Gray, Morgan A., Wei Hao, Förster, Helga, and Adaskaveg, James E.
- Subjects
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PHYTOPHTHORA , *CITRUS , *PHYTOPATHOGENIC microorganisms , *TOXICITY testing , *FUNGICIDES - Abstract
Phytophthora citrophthora, P. syringae, P. nicotianae, and P. hibernalis are important pathogens of citrus in California but few chemical treatments are currently available. In vitro toxicities of four new fungicides to isolates of Phytophthora spp. from California were determined. Mean effective concentration values to inhibit mycelial growth by 50% for ethaboxam, fluopicolide, mandipropamid, oxathiapiprolin, and mefenoxam were 0.068, 0.04, 0.004, 0.0003, and 0.039 μg/ml, respectively, for 62 isolates of P. citrophthora; 0.005, 0.045, 0.003, 0.0001, and 0.008 μg/ml, respectively, for 71 isolates of P. syringae; 0.016, 0.057, 0.005, 0.0005, and 0.183 μg/ml, respectively, for 31 isolates of P. nicotianae; and 0.030, 0.018, 0.005, <0.0003, and ≤0.001 μg/ml, respectively, for two isolates of P. hibernalis. Mean values for≥90%inhibition of sporangia formation of four isolates of P. citrophthora were 0.1, 0.28, 0.026, 0.005, and 55 μg/ml for ethaboxam, fluopicolide, mandipropamid, oxathiapiprolin, andmefenoxam, respectively. Zoospore cyst germination of P. citrophthora wasmost inhibited by oxathiapiprolin andmandipropamid. Chlamydospore formation of P. nicotianae was most sensitive to oxathiapiprolin, with a mean ≥90% reduction (EC≥90) of 0.002 μg/ml, moderately sensitive to mandipropamid (EC≥90 = 0.2 μg/ml) and mefenoxam (EC≥90 = 0.6 μg/ml), and least sensitive to ethaboxam and fluopicolide (EC≥90 = 1 μg/ml). Oospore formation of P. nicotianae was inhibited by ≥90% using oxathiapiprolin at 0.0004 μg/ml, mandipropamid at 0.02 μg/ml, ethaboxam at 0.1 μg/ml, or fluopicolide at 0.4 μg/ml, whereas 62% inhibition was obtained by mefenoxam at 40 μg/ml. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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