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The Role of Partial Resistance in the Management of Cercospora Leaf Spot of Peanut in North Carolina. C. S. Johnson, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; M. K. Beute, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 76:468-472. Accepted for publication 14 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-468.

The effects of partial resistance to Cercospora arachidicola in combination with various rates of chlorothalonil were tested in field experiments conducted in North Carolina in 1982-1984. Areas under disease progress curves (AUDPCs) for percent infected leaflets and percent defoliation were lower on NC 5 than on Florigiant in 1982 and 1984. AUDPCs declined linearly with increasing fungicide rate on both cultivars. Proportional reductions in AUDPCs per unit of fungicide applied were similar for both cultivars in 1982. Infection and defoliation rates were reduced by both host resistance and increasing dosages of chlorothalonil. Infection rates declined more rapidly with increasing fungicide dosages on Florigiant than on NC 5. Decreases in defoliation rates, however, were similar for the two cultivars over all chlorothalonil dosages tested. Effects of disease control on yield, gross economic value, and net return to management of Cercospora leaf spot were observed only in 1982. Higher yields and economic returns were observed with NC 5 than with Florigiant at all levels of control. The 'fungicide equivalence' of NC 5 relative to Florigiant was estimated to be 1.4 L/ha per application when AUDPCs for percent infected leaflets were regressed against fungicide rate. Net return to leaf spot management activities on Florigiant was optimized at 2.5 L of chlorothalonil per hectare. Yields and economic returns, however, continued to increase with increasing dosage of fungicide on NC 5. The greatest benefit from the partial resistance to Cercospora leaf spot possessed by NC 5 appears to be in terms of increasing yield and gross economic value rather than in the reduction of recommended fungicide dosage.

Additional keywords: Arachis hypogaea, early leaf spot, epidemiology.