A simplified version of the weather-based advisory program developed by Parvin, Smith, and Crosby (PSC) for scheduling fungicide sprays for management of early leaf spot (Cercospora arachidicola Hori) of peanut (Arachis hypogea L.) was evaluated under various productions systems in Oklahoma from 1990-1992. Over eight trials with spanish cultivars, the number of sprays per season averaged 5.7 for the 14-d schedule and 4.0 for the advisory program. Final disease incidence (symptomatic and defoliated leaflets) with the fungicide chlorothalonil (1.26 kg/ha) averaged 15% for the 14-d schedule, 34% for the advisory program, and 77% for the control. However, disease incidence (75%) and defoliation (50%) approached unacceptable levels on the spanish cultivars in some trials. In six trials with runner cultivars, the number of sprays averaged 6.7 for the 14-d schedule and 4.7 for the advisory program. Final disease incidence with chlorothalonil on the runner cultivars averaged 5% for the 14-d schedule, 14% for the advisory program, and 68% in the control. Yields did not differ in any of the 14 trials between the advisory and 14-d programs using chlorothalonil. Yields averaged 3015, 3003, and 2303 kg/ha for spanish cultivars and 4108, 3855, and 3066 kg/ha for runner cultivars with the 14-d schedule, advisory program, and control, respectively. The advisory program was effective in irrigated trials where weather stations were deployed either under or outside the influence of irrigation. The fungicides tebuconazole at 0.14 kg/ha and propiconazole at 0.13 kg/ha generally provided better leaf spot control with the advisory program than chlorothalonil. The post-infection activity of these fungicides was observed in one trial and probably accounts for their improved performance. Yields were reduced and leaf spot incidence was high where tank mixes of benomyl (0.28 kg/ha) or thiophanatemethyl (0.38 kg/ha) plus mancozeb (1.68 kg/ha) were used with the advisory program. Area under the disease progress curve, leaf spot incidence, and defoliation in the controls were lower for runner than for spanish cultivars at sites where both market types were planted in adjacent trials. Fungicides applied according to the advisory program provided better leaf spot control on the runner cultivars. Results showed the need for a weather-based advisory which allows greater levels of leaf spot control on spanish cultivars than the PSC advisory.

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Author notes

1Approved for publication by the Director, Oklahoma Agric. Exp. Stn. This study was funded in part by Hatch project H2159, the Samuel Roberts Noble Foundation, and the Oklahoma Coop. Ext. Serv. IPM Project.