Simultaneous temporal progress of sorghum anthracnose and leaf blight in crop mixtures with disparate patterns

Field studies were conducted at Alupe in western Kenya in 1995 and 1996 to evaluate the efficacy of crop and species mixtures for the management of so rghum anthracnose (caused by Colletotrichum sublineolum) and leaf blight (c aused by Exserohilum turcicum). The progress of these diseases developing s imultaneously on a susceptible sorghum cultivar planted in inter- or intra- row mixtures of varying proportions with either maize or resistant sorghum was monitored. The effects of host type and mixture patterns on disease pro gress were compared by parameter estimates derived from fitted Lotka-Volter ra competition equations and nonlinear logistic models. Competition coeffic ients were not significant and their confidence intervals included zero in most cases, suggesting that interactions between C. sublineolum and E. turc icum did not occur. Mixtures of the susceptible sorghum with either the non host maize or the resistant sorghum delayed the time when disease is first observed and reduced the rate of disease progress and carrying capacity for both anthracnose and leaf blight, with a more pronounced effect on the lat ter disease. The lower efficacy of mixtures in reducing anthracnose was att ributed to an aggregated spatial pattern, coupled with higher rates of prog ress for this disease. Intra-row mixtures were more efficient than inter-ro w mixtures in reducing disease development in all years. The implications o f these observations for the management of sorghum diseases under small-sca le farming systems are discussed.