Management of Early Leaf Spot of Peanut as Affected by Fungicide and Date of Spray Program Initiation

Abstract

A fungicide program for control of early leaf spot (Cercospora arachidicola) of peanut (Arachis hypogaea) in Georgia typically consists of a full-season program initiated ca. 30 days after planting (DAP) that includes seven applications made on 14-day intervals. Field tests were conducted in Tifton and Plains, GA in 2001 and 2002 to compare full-season and reduced programs of the fungicides pyraclostrobin (168 g a.i./ha), chlorothalonil (1.26 kg a.i./ha), and tebuconazole (227 g a.i./ha). Reduced fungicide programs were achieved by delaying initial applications at 14-day intervals from ca. 30 DAP to 45 through 105 DAP, totaling from 6 to as low as 2 applications per season, respectively. In 2003 and 2004, full-season programs of the fungicides pyraclostrobin and chlorothalonil were compared to reduced programs of pyraclostrobin. Reduced programs that received 6 and 5 applications were achieved by delaying the initial applications from ca. 30 DAP to 45 and 60 DAP, respectively. In 2001 and 2002, control of early leaf spot with pyraclostrobin was superior to that with chlorothalonil or tebuconazole within the respective initiation dates. Delaying the initial application of pyraclostrobin up to 60 DAP gave better control of leaf spot than for full-season programs of chlorothalonil or tebuconazole. Fungicide programs had no effect on yield at Plains in 2001 or Tifton in 2002. At Tifton in 2001 and Plains in 2002, yield decreased according to quadratic functions of time of spray initiation, with no indication of yield reduction until fungicide programs were initiated after 60 to 70 DAP. In 2003 and 2004, reduced programs of pyraclostrobin resulted in final levels of leaf spot that were similar to or lower than those in plots receiving a full-season program with chlorothalonil. Across both years, yields of reduced programs with pyraclostrobin were similar to those of full programs of either chlorothalonil or pyraclostrobin. Accepted for publication 11 December 2005. Published 14 February 2006.