Field tomatoes were sprayed with chlorothalonil on a fixed–interval spray program and a TOM–CAST spray program with disease severity value threshold of 18. Foliage samples from upper and lower canopy layers were collected prior to spray re–applications. Chlorothalonil residue data were compared to the chlorothalonil efficacy threshold (1.2 μg/cm2). Using a seven–day interval program, eight of the nine and seven of the nine spray intervals had chlorothalonil residues above the critical level for the upper and lower canopy layers, respectively. Using the TOM–CAST program, four of the five spray intervals had chlorothalonil residues above the critical level for both upper and lower canopy layers when the DSV threshold of 18 was reached. Persistence of chlorothalonil residues at effective concentrations could lengthen the spray interval beyond the DSV–based spray recommendation.

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Published in Applied Engineering in Agriculture, v. 17, issue 4, p. 445-448.

© 2001 American Society of Agricultural Engineers

The copyright holder has granted the permission for posting the article here.

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This research was supported by the North Central Region Pesticide Impact Assessment Program (NCRPIAP), and the United States Department of Agriculture National Research Initiative Grants Program (USDA–NRI).

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The investigation reported in this paper (No. 98–05–124) is part of a project of the Kentucky Agricultural Experiment Station and is published with approval of the director.