In vitro insensitivity to metalaxyl of isolates of Phytophthora citricola and P. parasitica from ornamental hosts in southern California

In vitro sensitivity to metalaxyl was evaluated for 13 isolates of Phytophthora citricola and 26 isolates of P. parasitica recovered from ornamental hosts or soil from 12 locations in southern California. One isolate of P. citricola from azalea and two isolates of P. parasitica from periwinkle were insensitive to metalaxyl. Mean EC 50 values for inhibition of linear growth were 219.9 yg a.i./ml for the metalaxyl-insensitive isolate of P. citricola and 717.4 and 742.4 yg a.i./ml for the two metalaxyl-insensitive isolates of P. parasitica