Dark leaf spot (Alternaria brassicicola) on Chinese cabbage:: spatial patterns

The spatial spread of dark leaf spot caused by Alternaria brassicicola on Chinese cabbage was characterised over 2 years. The study was conducted in 2 field trials using ordinary runs, mapping, spatial autocorrelation, and 2-dimensional distance class analyses. Diseased plants were generally clustered and cluster orientation coincided with the line of inoculation. Disease spread was greater within than across rows. The maximum number of spatial lags with significantly positive autocorrelations occurred when disease incidence levels reached 20-80% in summer 1993-94. Core cluster size generally increased with disease incidence. Two-dimensional distance class analysis was the best analytical method among those used in describing spatial spread of the disease as it did not only provide maximum information but also considered missing data.