Baseline sensitivity of Phytophthora capsici isolates from the southeast US to mandipropamid

The plant pathogen Phytophthora capsici is rapidly becoming an important limiting factor in vegetable production in the southeastern United States. In 2008, a new fungicide, mandipropamid (trade name: Revus) was labeled for managing P. capsici on vegetable crops. In this study we used a collection of 28 P. capsici isolates from the southeastern United States to determine baseline sensitivity values to this new fungicide. Of these 28 isolates, 5 were from NC, 8 from SC, 9 from GA, and 6 from FL. All isolates were confirmed as P. capsici based on morphology and by using P. capsici-specific PCR primers. An in vitro biological growth assay using V8-juice agar amended with four concentrations of mandipropamid (0, 0.0015, 0.015, 0.15 mg/L) was used to determine EC sub(50) values. The EC sub(50) values for mycelial growth on amended media ranged from 0.0125 mg/L to 0.0292 mg/L (mean = 0.0219 mg/L). Mycelial growth of all isolates was completely inhibited at 0.15 ppm. EC sub(50) values for production of sporangia ranged from