Open AccessSensitivity of Populations of Phytophthora capsici from South Carolina to Mefenoxam, Dimethomorph, Zoxamide, and Cymoxanil
Author(s) -
Anthony P. Keinath
Publication year - 2007
Publication title -
plant disease
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.663
H-Index - 108
eISSN - 1943-7692
pISSN - 0191-2917
DOI - 10.1094/pdis-91-6-0743
Subject(s) - phytophthora capsici , fungicide , biology , blight , horticulture , phytophthora , metalaxyl , phytophthora infestans , botany
In summer and fall 2003, Phytophthora blight and crown rot, caused by Phytophthora capsici, was found in three fields each of summer squash and pepper on three farms in two counties in South Carolina. Although this disease had been confirmed previously in the state, five of these outbreaks were in fields thought to be free of P. capsici. The objectives of this study were to determine whether isolates of P. capsici in South Carolina were sensitive to mefenoxam and to determine baseline sensitivities to dimethomorph, zoxamide, and cymoxanil, fungicides recently registered to control Phytophthora blight. Of 120 isolates tested for sensitivity to mefenoxam at 100 mg/liter, 8 isolates were resistant (relative colony diameter [RCD] > 90% of nonamended control), 60 isolates were sensitive (RCD 50 mg/liter for cymoxanil. EC 50 values for zoospore cyst germination were 0.07 ± 0.02 mg/liter for dimethomorph and >50 mg/liter for cymoxanil. EC 50 values for zoospore production were 0.63 ± 0.42 mg/liter for dimethomorph, 0.47 ± 0.51 mg/liter for zoxamide, and <50 mg/liter for cymoxanil. Sensitivity values obtained in this South Carolina study can be used as a comparative baseline to monitor shifts in sensitivity to the fungicides mefenoxam, dimethomorph, zoxamide, and cymoxanil in populations of P. capsici.