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POSTERS: Chemical control

Population structure and fungicide sensitivity of Phytophthora capsici in Tennessee
Timothy Siegenthaler - University of Tennessee. Zachariah Hansen- University of Tennessee

Phytophthora blight of cucurbits and pepper, caused by the oomycete Phytophthora capsici, is one of the most destructive diseases vegetable growers face and management is extremely difficult. Little is known about fungicide sensitivity and population structure of P. capsici in Tennessee. In 2018, 87 single-zoospore isolates were obtained from infected fruit, stems or crowns collected from four different field sites throughout eastern and middle TN. All 87 isolates were tested against six fungicides using radial growth assays. Mefenoxam was tested at 10 ?g/ml and 100 ?g/mll. Five out of 87 isolates were found to be resistant and grew above 40% of the growth of the non-amended control at 10 ?g/ml and 100 ?g/ml mefenoxam. Dimethomorph was tested at five concentrations ranging from 0 ?g/ml to 1 ?g/ml and no resistance was found. EC50 values ranged from 0.21 ?g/ml to 0.60 ?g/ml. Fluopicolide was tested at five concentrations ranging from 0 ?g/ml to 5 ?g/ml. Thirty-six out of 87 isolates were resistant, with EC50 values >5 ?g/ml. Sensitive isolates had EC50 values ranging from 0.16 ?g/ml to 3.1 ?g/ml. Mandipropamid, cyazofomid and oxathiapiprolin testing is currently underway. All isolates were genotyped using 45 single nucleotide polymorphisms (SNPs) to explore population structure in TN. Information gained through this study will improve management recommendations, and will further our understanding of how P. capsici is distributed and proliferated throughout TN.