Synergistic Interactions of Cymoxanil Mixtures in the Control of Metalaxyl-ResistantPhytophthora infestansof Potato

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Abstract
Cymoxanil mixtures with either mancozeb (Mancur) or with mancozeb and oxadixyl (Pulsan, Sandocur-M) were effective in controlling both metalaxyl-sensitive (MS) and -resistant (MR) Phytophthora infestans in potatoes (cv. Alpha) in growth chambers. Metalaxyl-mancozeb (Ridomil-MZ) and oxadixyl-mancozeb (SAN-518) mixtures were effective against the MS fungus but not against the MR fungus. Mancur, Pulsan, and Sandocur-M were more effective in controlling both MS and MR isolates than were their individual ingredients. Increased efficacy of mixtures relative to their components combined (synergy factor) was calculated using both the Abbott-Colby and Wadely methods. Synergy factor values for the control of MS P. infestans were highest for Sandocur-M and lowest for SAN-518. We concluded that cymoxanil mixtures are suitable for late blight control in growing areas of Israel where MR P. infestans populations prevail.