The black rot caused by Xanthomonas campestris pv. campestris and Alternaria black spot caused by Alternaria brassicicola are significant cabbage diseases in the State of Pernambuco, Brazil. A lack of knowledge on the epidemiology of these diseases at a regional level motivated a comparative analysis of the epidemics in relation to temporal and spatial aspects. The study was performed in 1997 and 1998, on different plantations, each year, located in Camocim de São Félix, Agreste of Pernambuco. In each area, 1,920 plants were evaluated at weekly intervals for incidence and severity of both diseases. Healthy and diseased plants were spatially mapped. There are only small variations between the diseases in terms of the initial (y o) and maximum (y max) values for incidence and severity, the estimated rates of disease progress (k) and the area under disease progress curves (AUDPC). Differences were more evident between years. The highest disease intensities were observed in 1998, due to a large number of infected plants and debris next to the plantation, a fact not observed in 1997. The use of "ordinary runs", adjustment to the b-binomial distribution, and spatial autocorrelation analyses, in most of the situations evidenced an initial randomised pattern of diseased plants, which later became aggregated, thus indicating that the diseases may have originated from aloinfections through an external inoculum arrival followed by autoinfections caused by plant-to-plant dissemination
