Curvas de progresso e gradientes da vassoura-de-bruxa (Crinipellis perniciosa) em cacaueiros enxertados em Uruçuca, Bahia

Abstract

Witches' broom has been considered the most important cocoa disease in Brazil since its first outbreak in Bahia in 1989. The objective of this work was to evaluate the disease progress curve and the gradient of witches' broom based on symptoms on flushes and pods of cocoa. The experiment was carried out in Uruçuca, southeast of Bahia State, in an area of grafted cocoa trees with 16 different genotypes, at an age of approximately three years after grafting, from September 2001 to July 2002. Assessments of symptomatic branches and pods were done monthly. Three treatments were used: (i) phytosanitation at sixmonthly interval, (ii) monthly phytosanitation and (iii) monthly phytosanitation plus monthly fungicide application (cuprous oxide at a dose of 3g of a.i./plant/application). An adjacent area with abandoned cocoa trees showing high disease incidence was considered the main source of inoculum. In the temporal analysis, the monomolecular growth model was fitted to data and disease progress rates and determination coefficients were compared. A good fit for vegetative brooms and diseased pods was obtained with the monomolecular model. The final disease incidence in vegetative brooms and pods in the treatment that included the fungicide application was approximately five times lower than in the other treatments. Spatial analysis showed no evidence for a disease gradient. These results showed that the integration of cultural, chemical and genetic control methods allows a slower disease progress and lower final incidence of the disease.