Temporal progress and development of common rust of maize (Puccinia sorghi Schw.) and its effect on yield and yield components of hybrid maize varieties in eastern Ethiopia

Under favorable environmental conditions, common rust of maize is the most devastating foliar disease of maize. West Hararghe middle lands, Eastern Ethiopia are hot spot areas for the development of the disease. Field experiments were conducted to determine the temporal development of common rust and its effect on grain yield and yield components on hybrid maize varieties at Haramaya University, Chiro Campus, during the 2013 and 2014 cropping seasons. The experiment was arranged in split plot design with three replications under natural epidemics. A contact fungicide Mancozeb (75%WP) at different rates (control, 1.5, 3.0, 4.5 and 6.0 kg ha -1 ) was applied five times at every seven days during the experimental period. Data on agronomic and disease parameters were recorded from the middle two rows. From the combined analysis of variance, maize varieties showed significant differences with reaction to common rust of maize, indicating the existence of genetic variability among the selected varieties. Up to 65% and 52% common rust severity levels were recorded on the varieties BH-140 and Shone, respectively. There was also a significant difference in the overall mean of common rust severity, incidence and Area under Disease Progress Curve(AUDPC) values among the varieties and spray intervals. On BH-140 and Shone common rust was progressing at rate of 0.0850 and 0.0352 units per day, respectively. Critical point model was found to be better than multiple point model and AUDPC values in estimating the relationships between common rust severity and yield as well as most of the yield components(R 2 =96). The disease resulted in grain yield loss of up to 45%, 42% and 10% on BH-140, Shone and BH-660, respectively. Maximum yield reduction of 45% and severity of 65% were recorded from the unsprayed plots. In conclusion, application of Mancozeb at a rate of (4.5 and 6.0 kg ha -1 ) contributed in the reduction of the effect of the disease and its temporal development on maize varieties in sprayed plots. Therefore, an integrated disease management strategy (fungicide and host resistance) should be employed in managing this disease in the study area.