Combining Center Pivot Irrigation Applications of Chlorothalonil with a Moderately Resistant Cultivar for Control of Late Leaf Spot in Peanut. A. K. Culbreath, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748. T. B. Brenneman, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748. Plant Dis. 76:29-32. Accepted for publication 23 June 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0029.

The efficacy of center pivot irrigation applications (chemigation) of chlorothalonil at recommended rates (1.25 kg a.i./ha) was less than with conventional, ground spray applications for control of late leaf spot (Cercosporidium personatum) in Florunner (susceptible) and Southern Runner (moderately resistant) peanut (Arachis hypogaea) cultivars in 1989 and 1990. Final leaf spot ratings in chemigated plots of Florunner were lower (P ≤ 0.05) than those in untreated plots in both years and in 1989 were higher (P ≤ 0.05) than ratings of unsprayed plots of Southern Runner. Leaf spot ratings were lower in unsprayed and chemigated treatments for Southern Runner than for Florunner, respectively, in both years. In 1989, yields of both chemigated and untreated Southern Runner were higher (P ≤ 0.05) than those of untreated Florunner, whereas chemigation did not improve yield of Florunner. In 1989, plants of Florunner treated with chlorothalonil via a spray boom mounted on the center pivot (Pivot Agricultural Spray System [PASS]) had higher leaf spot ratings than plants receiving ground sprays of the same rate of fungicide application. Plants of Southern Runner receiving PASS-applied chlorothalonil had leaf spot ratings similar to those plants treated with ground sprays. Pod yields of plants of each cultivar treated with chlorothalonil via the PASS system were not different (P ≤ 0.05) from those receiving ground sprays. No differences in yield among treatments or between cultivars occurred in 1990.