Calendar-based and AU-Pnuts advisory programs with pyraclostrobin and chlorothalonil for the control of early leaf spot and stem rot on peanut1

Abstract

Efficacy of pyraclostrobin (two applications at 0.16 or 0.27 kg ai/ha) was evaluated in 2-, 3-, and 4-wk treatment programs with chlorothalonil for the control of early leaf spot and stem rot on the peanut cultivars Andru II, Carver, DP-1 in 2003 and the former two cultivars along with C-99R in 2004 and 2005. Applications were also scheduled using the AU-Pnuts leaf spot advisory in 2004 and 2005. In order to target both early leaf spot and stem rot, the two applications of pyraclostrobin, which were included in each calendar treatment schedule, were made approximately 60 and 90 days after planting. Chlorothalonil at 1.26 kg ai/ha filled the remaining application slots in the above treatment schedules. A 2-wk calendar chlorothalonil program was included as a control. A total of seven-, five-, and four-total fungicide applications were scheduled according to the 2-, 3, and 4-wk calendar schedules, while six fungicide applications were triggered in each year by AUPnuts. Cultivar 3 treatment interactions for early leaf spot, stem rot, and yield were not consistent across years; data were pooled across cultivars for analyses of fungicidal program effects. Single degree of freedom contrast analyses indicated that pyraclostrobin as part of a 2-wk fungicide programs provided better early leaf spot control in 2 of 3 study years compared to the chlorothalonilonly program. Yields tended to be higher with the pyraclostrobin/chlorothalonil programs than with chlorothalonil-alone. Application interval and pyraclostrobin concentration each had a significant impact on early leaf spot control. Pyraclostrobin at 0.27 kg ai/ha controlled early leaf spot better than the 0.16 kg ai/ha rate, and some yield increase was also observed. When pyraclostrobin was applied as part of the 2-wk interval programs, leaf spot control was better in two of three years than as part of the 3-wk interval programs, and consistently better than when part of the 4-wk interval programs. Incidence of stem rot was not influenced by pyraclostrobin rate or treatment interval. Yield response with pyraclostrobin/ chlorothalonil programs was consistently influenced by application interval, with the 2-wk intervals providing higher yield in two of three years compared to 3-wk application intervals. Yield for the 2-wk and AU-Pnuts advisory pyraclostrobin/chlorothalonil programs was also similar in one of two trials.