An experimental field study was carried out in Belém, Pará, Brazil, in order to monitor the evolution of two diseases in grafted and non-grafted plants: 1) the amount of cupuaçuzeiro (Theobroma grandiflorum) sprouts and flowers with symptoms of witches' broom and 2) the presence of basidiocarps of the pathogen Crinipellis perniciosa. Epidemiological models (logistic, Gompertz, logistic + logistic and Gompertz + Gompertz) were fit to biannual disease progress curves (1993 and 1994 for the incidence of the disease in the sprouts and for basidiocarp production in the sprouts) and annual (1994) for the disease incidence on flowers and for basidiocarps produced in the flowers. The sum of the two logistic equations fit well with biannual data and the logistic model fit the annual data. The appearance of symptoms was generally associated with the dry period, whereas the production of basidiocarps occurred during the rainy period. The amount of witches' broom was highest from July to October and the most fungus fruiting bodies was detected in May-July.
