Dark leaf spot (Alternaria brassicicola) on Chinese cabbage: temporal spread and its influencing factors

Abstract

Temporal spread of dark leaf spot on Chinese cabbage was studied in experimental plots for 2 years. The effect of row orientation, the orientation of inoculated plants, and irrigation system on disease incidence and the effect of average wind direction on disease spread were investigated. A line source of inoculum in each plot was used for the 1993–94 summer and the 1994 spring–summer field trials, and 3 line sources for a 1995 autumn field trial. Disease progressed more rapidly in the 1993–94 summer than in the 1995 autumn. Disease epidemic did not develop in the 1994 spring–summer when environmental conditions were unfavourable. Disease incidence was higher in plots with row orientation parallel to the average wind direction than in plots with row orientation at right angles to the average wind direction for both the 1993–94 summer and the 1995 autumn trials. In summer 1993–94, across-row inoculation resulted in higher disease incidence than row inoculation did. No difference in disease incidence occurred between channel irrigation and overhead irrigation plots. Secondary infections always occurred adjacent to the source of inoculum and disease spread was influenced by the prevalent wind direction.