Impact of Application Rate and Treatment Interval on the Efficacy of Pyraclostrobin in Fungicide Programs for the Control of Early Leaf Spot and Southern Stem Rot on Peanut1

Abstract In 1999, 2000, and 2001, efficacy of the strobilurin fungicide pyraclostrobin (Headline F500) for the control of early leaf spot and southern stem rot was compared to that of standard fungicide programs on peanut cv. Georgia Green produced under irrigation. When applied at 2 wk intervals in 1999 and 2001, programs that included pyraclostrobin at rates ranging from 0.08 to 0.22 kg ai/ha gave better control of early leaf spot than the recommended season-long chlorothalonil program and were at least as efficacious against this disease as tebuconazole and azoxystrobin. The level of early leaf spot control provided by 0.08 to 0.16 kg ai/ha of pyraclostrobin applied every 3 wk and by chlorothalonil at the recommended 2 wk interval was similar. In all 3 yr, incidence of southern stem rot on peanut treated with pyraclostrobin alone, tank-mixed with flutolanil, or alternated with tebuconazole was significantly below damage levels recorded in plots treated with chlorothalonil alone and was usually comparable to the level of disease control obtained with recommended tebuconazole, flutolanil, or azoxystrobin programs. Compared to chlorothalonil alone, yields of the pyraclostrobin-treated peanuts were significantly greater in 2000 and 2001 and generally did not significantly differ from those yields recorded with the tebuconazole, flutolanil, or azoxystrobin programs. While pyraclostrobin often gave similar southern stem rot control over a range of treatment intervals, the most consistent yield gains were obtained when this fungicide was applied every 2 wk.