Efficacy of Systemic and Contact Fungicide Mixtures in Controlling Late Blight in Potatoes

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Abstract
A single foliar spray of either metalaxyl, fosetyl A1, mancozeb, fentin acetate, folpet, chlorothalonil, captafol, or one of a mixture of them was applied to potted potato plants (cv. Alpha) 1 day before inoculating with either a metalaxyl-sensitive (MS) or -resistant (MR) field isolate of Phytophthora infestans. Systemic and contact fungicidal mixtures were far more effective in controlling both MS and MR isolates than individual components at corresponding concentrations combined. No such increased efficacy was exerted by mixtures of metalaxyl and fosetyl Al, nor by mixtures of mancozeb and fentin acetate. It is hypothesized that any two fungicides that differ in mode of action and in stage of fungal growth that they affect will exhibit increased control efficacy of late blight in potato.