Tank-Mix Applications of Cyproconazole and Chlorothalonil for Control of Foliar and Soilborne Diseases of Peanut. A. K. Culbreath, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748. T. B. Brenneman, F. M. Shokes, A. S. Csinos, and H. S. McLean. Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748; Department of Plant Pathology, University of Florida Research and Education Center, Quincy 32351; Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748; and Sandoz Agro North America, Inc., Cordele, GA 31015. Plant Dis. 76:1241-1245. Accepted for publication 28 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1241.

Field tests were conducted during 1989–1991 at Tifton and Plains, Georgia, and Marianna, Florida, to evaluate the efficacy of full-season applications of tank-mix combinations of cyproconazole at rates of 0.062 kg a.i./ha and 0.093 kg a.i./ha with chlorothalonil at 0.63 kg a.i./ha for control of late leaf spot, caused by Cercosporidium personatum; southern stem rot, caused by Sclerotium rolfsii; and Rhizoctonia limb rot, caused by R. solani, of peanut (Arachis hypogaea). In all years and locations, tank mixes with both rates of cyproconazole controlled leaf spot as well as or better than chlorothalonil alone. In nine of 11 trials, the incidence of southern stem rot was lower in plots treated with the high rate of cyproconazole tank mix than in plots treated with 1.26 kg a.i./ha of chlorothalonil alone. In 1989 and 1990, the incidence of stem rot in plots treated with the high rate cyproconazole tank mix was significantly lower (P ≤ 0.05) than that of plots treated with chlorothalonil plus pentachloronitrobenzene (PCNB) at 5.6 kg a.i./ha applied 60–70 days after planting. Severity of Rhizoctonia limb rot varied greatly but was lower (P ≤ 0.05) in at least one tank-mix treatment than with chlorothalonil alone or with chlorothalonil plus PCNB in both 1989 and 1990. In nine of 11 trials, control of the soilborne diseases with one or both cyproconazole treatments resulted in yield increases compared with treatments of chlorothalonil alone. Yields were higher in tank-mix treatments of cyproconazole plus chlorothalonil than in those of chlorothalonil plus PCNB in two of three trials.