Efficacy and Economics of Three Fungicide Application Schedules for Early Blight Control and Yield of Fresh-Market Tomato. Anthony P. Keinath, Assistant Professor; Department of Plant Pathology and Physiology, Clemson University, Coastal Research and Education Center, Charleston, SC 29414-5332. Virginia B. DuBose, Agricultural Science Associate II, Department of Plant Pathology and Physiology, Clemson University, Coastal Research and Education Center, Charleston, SC 29414-5332; and P. James Rathwell, Professor, Department of Agricultural and Applied Economics, Clemson, SC 29634-0355. Plant Dis. 80:1277-1282. Accepted for publication 26 July 1996. Copy right 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1277.

Three methods to schedule fungicide applications for control of tomato early blight were evaluated under coastal South Carolina conditions in spring 1994 and 1995. Weekly fungicide applications, applications based on visual scouting according to the South Carolina Tomato 1PM Program, and applications called for by the TOM-CAST program with a threshold of 18 or 25 disease-severity values were compared with a nonsprayed control. Scouting and TOM-CAST reduced the number of fungicide applications to 4 and 6, respectively, compared with 10 weekly applications. In both years, all plots receiving fungicide had less blighted foliage than the non-sprayed control plots, which averaged 24.8% early blight severity at the end of the season. Area under the disease progress curve was lowest with the weekly or TOM-CAST schedules, intermediate with scouting, and highest with no fungicide. Mean yield of extra-large (≤70 mm diameter) mature green and pink fruit was 2.9 t/ha (28%) greater (P ≤ 0.05) with the weekly or TOM-CAST schedules than with scouting or no fungicide. Crop value and net return were not significantly affected by fungicide applications. Treatment costs (fungicide scheduling plus application costs) were highest for weekly applications but averaged 26 to 46% less for scouting and TOM-CAST. Early blight severity at the end of the season was lower on the tolerant cultivar Mt. Pride than on the susceptible cultivar Sunny in 1995 but not in 1994. TOM-CAST could be implemented by growers of fresh-market, mature green tomato in the coastal plain of the southeastern United States to effectively manage early blight.

Keyword(s): Alternaria solani, chlorothalonil, mancozeb