Abstract
Seven epidemics of cowpea severe mosaic (CPSM) on vegetable cowpea (Vigna unguiculata (L.) Walp.) were studied in the two seasons of the year in Trinidad, four in the rainy season and three in the dry season. Observations were made over time on the numbers and positions of diseased plants. Final disease incidence varied from 7 to 91 % and in relation to the incidence at first observation. Ordinary runs analysis of spatial disease distribution showed that this was initially random but became clustered with time, demonstrating for the first time that CPSM epidemics were polycyclic. The progress curves of the epidemics were all sigmoid and best fitted by the Gompertz model rather than the logistic model. Infection rates varied from 0.023 to 0.092 and were dependent on the level of initial disease. The temporal and spatial characteristics of the epidemics were similar in both seasons but the time to first significant clustering of diseased plants was generally shorter in the dry season. The epidemiology of CPSM in the two seasons of the year is discussed.
