Synergistic interactions between phenylamide fungicides and respiration inhibitors in controlling phenylamide-resistant populations of Phytophthora infestans on potato tuber disks

The efficacy of mixtures of respiration inhibitors and phenylamide fungicides (oxadixyl and metalaxyl) in controlling late blight was investigated using potato tuber disks. Results showed that uncoupling agents (e.g. DNP), inhibitors of ATP formation (e.g. oligomycin), ionophores (e.g, valinomycin) and inhibitors that block specific carriers in the electron transport chain (e.g. rotenone, antimycin A) increased significantly the control efficacy of both metalaxyl and oxadixyl towards populations of Phytophthora infestons when applied to tuber slices pretreated with sublethal doses of both fungicides. When applied alone at the same doses, respiration inhibitors did not inhibit the development of the late blight fungus. Increased control efficacy of mixtures was not noted against phenylamide-sensitive populations of the fungus.