Association of maize rust and leaf blight epidemics with cropping systems in Hararghe highlands, eastern Ethiopia

Two hundred and eight fields in the Hararghe highlands (Habro, Chercher and Wobera areas), Ethiopia were surveyed during the 1998 and 1999 cropping seasons to determine the occurrence, distribution and importance of maize rust and leaf blight (LB) in five types of maize cropping systems. Sixty four percent of the surveyed fields were intercropped with the proportion of maize ranging from 24% to 68%. Rust incidence and severity among the areas and between years varied. Logistic regression was used to analyse the association of the diseases with cropping systems and practices, geographic area, season and altitude. Crop density, sowing date, variety, area, cropping system and year were significantly associated with rust incidence in a multiple variable model. Low rust incidence had a high probability of association to low crop density, early and optimum sowing, maize-bean intercropping and the 1998 cropping season. High rust incidence had a high probability of association to the Habro area, hybrid varieties and maize-sorghum intercropping. Cropping year and proportion of maize in intercrops were significantly associated with rust severity in a multiple variable model. The severity of rust was higher where the proportion of maize in the intercrop was 25-50%. The Habro area and the 1998 season had a high probability of association with high rust severity. Crop density, altitude and sowing date were significantly associated with LB incidence in a multiple variable model. Sowing at an optimum time had a high probability of association with low (< 25%) LB incidence. At low crop density and lower altitude LB was increased. (C) 2001 Elsevier Science Ltd. All rights reserved.