Effects of sowing date and fungicide application on yield of early and late maturing peanut cultivars grown under rainfed conditions in Ghana

Late leaf spot is one of the important factors limiting peanut productivity in Ghana. It is essential to demonstrate the extent of yield losses caused by leaf spot and to develop suitable crop management practices. The objectives of this research were to study the effects of time of sowing, cultivar lifecycle, and fungicide sprays on disease incidence, biomass and pod yield of peanut crops grown under rainfed conditions in northern Ghana. Two peanut cultivars, Chinese (90 days duration) and F-mix (120 days duration) were grown for three seasons (1999-2001) at Nyankpala and for two seasons (2000, 2001) at Wa with three sowing dates (early, mid and late, relative to start of rainy season) with (+F) and without (-F) fungicide application. Disease rating, main-stem defoliation, total biomass, pod yield and seed yield were recorded at harvest maturity. Early sowings soon after onset of rains resulted in greater biomass and pod yields compared to late sowing for both cultivars. The long duration cultivar F-mix produced greater yields than short duration cultivar Chinese under both with and without fungicide treated environments. However, incidence and severity of disease, as measured by disease scores and main-stem defoliation at the end of season, were similar in both cultivars. This suggests that the greater yield obtained by the long duration cultivar was not due to disease tolerance or escape but due to its longer growing season. Application of foliar sprays of fungicide was effective in controlling leaf spot and improved peanut biomass and pod yields by 39% and 75%, respectively, when averaged across cultivars and years. Long duration cultivar F-mix, sown early and treated with fungicide under optimum and timely crop management practices, produced 4500-5000 kg ha(-1) pod yield over five site years, i.e. more than three to four-fold increase over present average yields in Ghana.