Efficacy of Dicarboximide Fungicides and Fungicide Combinations for Control of Botrytis Leaf Blight of Onion in New York. J. W. Lorbeer, Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853. P. C. Vincelli, Research Assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853. . Plant Dis. 74:235-237. Accepted for publication 6 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0235.

Iprodione and vinclozolin provided partial control of Botrytis leaf blight of onion when used alone at moderate to high rates (1.12–2.24 kg/ha). Disease control achieved with the dicarboximide fungicides was improved when they were mixed with other protectant fungicides, even at rates of the dicarboximide fungicides as low as 0.56 kg/ha. Excellent disease control was obtained by mixing iprodione (0.56 kg/ha) and chlorothalonil (0.58–0.87 kg/ha) with either maneb + zinc (2.69 kg/ha) or mancozeb (1.79 kg/ha). Use of these mixtures would improve the cost-effectiveness of iprodione and vinclozolin and reduce the potential for development of Botrytis squamosa populations resistant to these fungicides.