Effect of Northern Leaf Blight (Exserohilum Turcicum) Severity on Yield of Maize (Zea Mays L.) in Morogoro, Tanzania

Grain yield losses of five varieties of maize due to northern leaf blight (NLB) were evaluated in the Sokoine University of Agriculture, Morogoro crop museum using artificial inoculation. The experiment was laid out in two blocks of E. turcicum inoculated and mancozeb treatment plots, arranged in randomized complete block design in three replicates. Data on disease severity base on percent leaf area affected and yields were subjected to analysis of variance while significant means were separated using Turkeys. Correlations and coefficient of determination analysis were used to determine the relationship and reliability of the critical point models. Results showed that the maize varieties Bora, Kilima, Situka-1, Staha and Tmv-1 were highly susceptible to NLB. Percent disease index (PDI) varied from 63.3 % in Kilima to 87 % in Staha. Consequently, proportional grain yield losses of 23.9 - 40.4 % and 11.2 - 36.1 % were recorded for grain yields (tons/ha) and 1000 grain weight (g/plot), respectively. It was also found that mancozeb sprays completely protected and increased yield of the maize varieties. The average PDI estimated at silk dry significantly (p- 0.05) and negatively correlated with yields while coefficient determination values R = 0.35 - 0.97 and R = 0.54 - 0.99 for yield measured in tons/ha and g/plot, respectively, confirmed the reliability of the crop models. Although the critical point model indicated good fit for the two years, yield loss models varied within varieties for the two years.