Strategies for Chemical Control of Snap Bean Rust in Florida and Their Compatibility with Canadian Residue Tolerances. Ken Pohronezny, Associate Professor (Pest Management), IFAS, University of Florida, Tropical Research and Education Center, Homestead 33031. Joyce Francis, and W. George Fong. Biological Scientist II, IFAS, University of Florida, Tropical Research and Education Center, Homestead 33031, and Chief, Bureau of Chemical Residue Laboratory, Division of Chemistry, Florida Department of Agriculture and Consumer Services, 3125 Conner Blvd., Tallahassee 52301. Plant Dis. 71:639-642. Accepted for publication 10 December 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0639.

Chemical control of snap bean rust using crop phenology as a basis for spray application was equivalent to the standard practice of full-season use of ethylene bisdithiocarbamate (EBDC) fungicide (maneb or mancozeb) plus sulfur. A maneb or mancozeb plus sulfur tank mix applied weekly until flowering was followed by two or three applications of chlorothalonil. EBDC residues in the crop phenology system were less than 0.1 ppm, whereas full-season use of EBDC plus sulfur in one of the two years of testing resulted in residues five times larger than the 0.1-ppm Canadian tolerance. Spray programs using the crop phenology method or full-season use of 1.17 kg a.i./ha chlorothalonil also were found to be cost-effective means for snap bean rust control while maintaining fungicide residues within limits established by the Canadian government. Bitertanol, a currently unregistered fungicide, provided outstanding rust control when used as a routine spray or when weekly sprays were initiated after rust appearance (on-demand).