Temporal Dynamics of Chlorothalonil Residues on Peanut Foliage and the Influence of Weather Factors and Plant Growth. V. J. Elliott, U.S. Department of Agriculture, Agricultural Research Service, Crops Research Laboratory, Box 1168, Oxford, NC 27565, and Department of Plant Pathology, North Carolina State University, Raleigh 27695. H. W. Spurr, Jr., U.S. Department of Agriculture, Agricultural Research Service, Crops Research Laboratory, Box 1168, Oxford, NC 27565, and Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 77:455-460. Accepted for publication 9 December 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-0455.

The persistence of chlorothalonil residues on foliage of peanut (Arachis hypogaea) cultivar Florigiant was evaluated under field conditions. Chlorothalonil (Bravo 720) was applied at 1.26 kg a.i./ha with a boom sprayer. The results of seven trials over 3 yr yielded an average decay rate of –0.051 μg/cm² per day, with values ranging from –0.093 to –0.036. This corresponds to a mean half-life of 13.6 days, with values ranging from 7 to 19 days. Decay rates increased with increasing rainfall. No influence of temperature on decay rates could be detected. A simulation model was developed to examine the effects of new leaf emergence on the measurement of residue dynamics. With the diluting influence of new leaf emergence, apparent residue half-life decreased from a true half-life of 13.6 days to 6.4 days. The model also demonstrated that because of new leaf emergence, significant amounts of unprotected foliage developed during the interval between successive fungicide applications.