Turcicum leaf blight (Exserohilum turcicum) (TLB) is a major disease affecting maize (Zea mays) in western Ethiopia. This study was designed to: assess the incidence and severity of TLB in major highland and mid-altitudes of maize growing agro-ecologies of Western Oromia, map the geographical distribution of the TLB disease in the study area, and evaluate the reaction of maize varieties under production to TLB. From each representative zone, 2 - 12 districts were surveyed based on production of maize and 8 - 73 fields each averaging 1 ha at the interval of 5 - 10 km were assessed per zone. Such fields were randomly selected on both sides of the road. Each sampling point was marked with the global positioning system (GPS) using GPS receiver for altitude and co-ordinates. In each field, 9 m² areas were marked out in three randomly selected points in a diagonal form using meter tap. Ten stands of maize plant in the middle of each marked area were randomly selected and assessed for incidence and severity. Survey was conducted on 172 farmers’ fields in 29 districts and five zones of major maize growing agro ecologies in western Oromia region of Ethiopia. Survey results revealed the prevalence of TLB across all the districts albeit at different levels. Mean TLB incidence ranged from 16.3% in Abay chomen to 96.67% in Wayu Tuka and mean percent severity index varied between 3.1% in Abay chomen and 57.5% in Lalo Assoabi district. The overall mean incidence and PSI were high (up to 74.1 and 34.7%, respectively) during the grain filling stage of maize compared to tasseling and silking stage of the crop. Most of maize varieties under production were found to be affected by TLB, while fertilizer application reduced the intensity of disease. Successive survey for TLB in all the maize producing areas across the country should be carried out to have a complete picture on the importance of the disease across geographic regions and agro ecologies, to identify sources of resistant genotypes and the pathotypes/available in Ethiopia, and to associate weather variables with the development of TLB.
Key words: Distribution, Exserohilum turcicum, maize, turcicum leaf blight, Incidence, percent severity index.
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