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The Effects of Particle Size and Distribution on Performance of the Fungicide Chlorothalonil. P. A. Backman, Assistant Professor, Department of Botany and Microbiology, Auburn University Agricultural Experiment Station, Auburn, AL 36830; G. D. Munger(2), and A. F. Marks(3). (2)Manager, Commercial Development, Agricultural Chemicals Division, Diamond Shamrock Corporation, Cleveland, OH 44114; (3)Group Leader, Formulations, Diamond Shamrock Corporation, T. R. Evans Research Center, Painesville, OH 44077. Phytopathology 66:1242-1245. Accepted for publication 1 April 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1242.

Flowable preparations of chlorothalonil (tetrachloroiso-phthalonitrile) prepared by wet milling had reduced particle sizes and better fungicidal performance than standard air-milled preparations. Fungicidal efficacy in the field was affected more by distribution profile of particles than by absolute numbers of particles, or total surface area per gram. Field applications of 30-50% lower dosages of wet-milled formulations of chlorothalonil provided control equivalent with full dosages of the commercial air-milled formulation. Wet-milling and particle-size distribution studies provide a key to increasing performance of chlorothalonil, and possibly to many other fungicides of low water solubility.

Additional keywords: pesticide persistance, disease control, Cercospora, Cercosporidium, peanuts, fungicide formulation.