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Synergistic Interactions of Cymoxanil Mixtures in the Control of Metalaxyl-Resistant Phytophthora infestans of Potato. Yair Samoucha, Postdoctoral research assistant, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52100, Israel; Yigal Cohen, Professor, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52100, Israel. Phytopathology 78:636-640. Accepted for publication 21 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-636.

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.

Additional keywords: acylanilides, chemical control, fungicide interaction, oomycetes, phenylamides.