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Disease Control and Pest Management

Control of Metalaxyl-Resistant Causal Agents of Late Blight in Potato and Tomato and Downy Mildew in Cucumber by Cymoxanil. Yigal Cohen, Professor, Department of Life Sciences, Bar-Ilan University, 52100 Ramat-Gan, Israel; Masha Grinberger, Technician, Department of Life Sciences, Bar-Ilan University, 52100 Ramat-Gan, Israel. Phytopathology 77:1283-1288. Accepted for publication 20 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1283.

A relatively high dosage of cymoxanil foliar spray was required to control late blight in potato and downy mildew in cucumber in growth chambers. ED90 values for control of metalaxyl-sensitive field isolates of Phytophthora infestans ranged between 164 and 459 μg/ml, and for metalaxyl-resistant isolates, between 112 and 525 ?g/ml. ED90 values for control of metalaxyl-resistant isolates of Pseudoperonospora cubensis ranges between 201 and 878 μg/ml. Complete control of both pathogens was achieved at concentrations between 500 and > 1,000 μg/ml. Preventive and curative efficacy of the fungicide lasted for 5 and 3 days, respectively. Cymoxanil was readily taken up by leaves, roots, and stems. When applied to roots and stems, it showed acropetal systemic translocation in cucumber and tomato but not in potato. No systemic translocation occurred when applied to leaf laminae. Translaminar translocation occurred in potato and tomato but not in cucumbers. The fungicide was toxic to roots of tomato plants.

Additional keywords: Oomycetes, systemic fungicides.