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Effect of Application Frequency and Reduced Rates of Acibenzolar-S-Methyl on the Field Efficacy of Induced Resistance Against Bacterial Spot on Tomato

February 2012 , Volume 96 , Number  2
Pages  221 - 227

Cheng-Hua Huang and Gary E. Vallad, Gulf Coast Research and Education Center, University of Florida, IFAS, Wimauma 33598; Shouan Zhang, Tropical Research and Education Center, University of Florida, IFAS, Homestead 33031; Amin Wen, Department of Plant Pathology, North Dakota State University, Fargo 58108; Botond Balogh, Jose Francisco L. Figueiredo, Franklin Behlau, Jeffrey B. Jones, and M. Timur Momol, Department of Plant Pathology, University of Florida, Gainesville 32611; and Steve M. Olson, North Florida Research and Education Center, University of Florida, Quincy 32351

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Accepted for publication 31 August 2011.

Acibenzolar-S-methyl (ASM), a plant activator known to induce systemic acquired resistance, has demonstrated an ability to manage a number of plant diseases, including bacterial spot on tomato caused by four distinct Xanthomonas spp. The aim of this study was to evaluate application rate and frequency of ASM in order to optimize field efficacy against bacterial spot in Florida, while minimizing its impact on marketable yields. ASM was applied biweekly (once every 2 weeks) as a foliar spray at a constant concentration of 12.9, 64.5, and 129 μM throughout four field experiments during 2007–08. A standard copper program and an untreated control were also included. Overall, biweekly applications of ASM did not significantly reduce disease development or the final disease severity of bacterial spot compared with the copper-mancozeb standard or the untreated control. Only one experiment showed a significant reduction in the final disease severity on plants treated with ASM at 129 μM compared with the untreated control. Three additional field trials conducted during 2009–10 to evaluate the effects of weekly and biweekly applications of ASM at concentrations of 30.3 to 200 μM found that weekly applications provided significantly better disease control than biweekly applications. The tomato yields were not statistically improved with the use of ASM relative to the untreated control and standard copper program. Weekly ASM applications at rates as low as 75 μM (equivalent to 1.58 g a.i./ha in 100 liters of water or 0.21 oz. a.i./acre in 100 gallons of water) to 200 μM (equivalent to 4.20 g a.i./ha in 100 liters of water or 0.56 oz. a.i./acre in 100 gallons of water) were statistically equivalent in managing bacterial spot of tomato without significantly reducing yield compared with the untreated control.

© 2012 The American Phytopathological Society