The Role of Partial Resistance in the Management of Cercospora Leaf Spot of Peanut in North Carolina

Abstract

The effects of partial resistance to C. arachidicola [Mycosphaerella arachidis] in combination with various rates of chlorothalonil were field tested in 1982-84. Areas under disease progress curves (AUDPCs) for percent infected leaflets and percent defoliation were lower on groundnut cv. NC 5 than on Florigiant in 1982 and 1984. AUDPCs declined linearly with increasing rate on both cultivars. Proportional reductions in AUDPCs/unit of applied were similar for both in 1982. Infection and defoliation rates were reduced by both host resistance and increasing dosages of chlorothalonil. Infection rates declined more rapidly with increasing dosages on Florigiant than on NC 5. Decreases in defoliation rates, however, were similar for both over all chlorothalonil dosages tested. Effects of disease control on yield, gross economic value and net return to management of the disease 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/application was estimated to be 1.4 litre/ha when AUDPCs for percent infected leaflets were regressed against rate. Net return to leaf spot management activities on Florigiant was optimized at 2.5 litre chlorothalonil/ha. Yields and economic returns, however, continued to increase with increasing dosage of on NC 5. The greatest benefit from the partial resistance possessed by NC 5 appears to be in terms of increasing yield and gross economic value rather than in the reduction of recommended dosage