Comparison of Fungicide Programs for the Control of Early Leaf Spot and Southern Stem Rot on Selected Peanut Cultivars1

Abstract Azoxystrobin, tebuconazole, pyraclostrobin, chlorothalonil + flutolanil, and chlorothalonil fungicide programs were evaluated on selected peanut cultivars for the control of early leaf spot (ELS) and southern stem rot (SSR) in 2000, 2001, and 2002. A peanut-cotton-peanut rotation was followed and the plots were irrigated as needed. Virugard and Georgia Green were planted in all 3 yr. The late-maturing line Southern Runner was planted only in 2000 and was replaced with Florida C-99R in 2001 and 2002. Since the ranking of fungicide programs for ELS and SSR control and yield response was similar over peanut cultivars, data for each variable in 2000, 2001, and 2002 were pooled. The 0.34-kg ai/ha azoxystrobin and pyraclostrobin programs gave better ELS control than the season-long chlorothalonil standard in 1 yr. However, SSR control and yield response to pyraclostrobin was similar to the chlorothalonil standard. Significant reductions in SSR damage and higher yields were obtained with 0.34-kg ai/ha azoxystrobin program in all 3 yr. When compared to the chlorothalonil standard, the 0.47-kg ai/ha azoxystrobin program gave superior SSR control in 2000 and 2001, but significantly better ELS control and higher yield were obtained only in 2001. Tebuconazole-treated peanuts had similar ELS ratings to those recorded for the chlorothalonil standard and azoxystrobin programs in 2000 and 2001, but the ELS ratings for the former program were significantly higher in 2002. While tebuconazole reduced SSR damage compared with chlorothalonil alone, the azoxystrobin and chlorothalonil + flutolanil programs controlled SSR significantly better than tebuconazole in at least 1 yr. Also, the 0.34-kg ai/ha azoxystrobin program significantly increased yield above that of the chlorothalonil standard more consistently than did tebuconazole. Relatively few differences in disease control or yield response were noted between the two chlorothalonil + flutolanil programs, but both increased yield above that of the chlorothalonil standard. By maturing about 2 wk before Georgia Green, Virugard may have escaped some ELS and SSR damage, which may have contributed to its higher yield. There are indications that the late-maturing Florida C-99R has partial resistance to ELS but not SSR. Georgia Green proved more susceptible to both diseases than Virugard or Florida C-99R but no peanut cultivar produced consistently higher yields.