Powdery mildew progress according to cashew phenology

ABSTRACT Powdery mildew (Pseudoidium anacardii) quantitatively and qualitatively decreases cashew production in different regions of Brazil. Severe epidemics are frequent, starting during flowering and extending to the end of the plant production cycle. The disease progress is related to the inoculum density in the area with cashew trees, to the environmental factors and to the susceptibility of the plant organs to infection. Given the lack of information on the epidemiology of this disease, the present study aimed to characterize powdery mildew progress in dwarf cashew trees according the plant phenology. Six treatments corresponding to the phenological protection periods were used, including the application of sulfur fungicide to quantify powdery mildew severity in two successive flowering stages. The collected data were used to generate disease progress curves adjusted to linear models. The Monomolecular model best fit to the powdery mildew progress curves for the panicles in periods I and II in the absence of protection with sulfur. According to the Monomolecular model, powdery mildew progress rates were greater in period I compared to period II. On the other hand, the Logistic model showed the best fit when sulfur was introduced to protect the panicles and reduce the epidemics. For longer periods of protection, the models could not be fit due to the low severity of powdery mildew. The Monomolecular model can be used to estimate the disease progress rate, and the delay in the beginning of the epidemics is directly related to the increase in the protection of panicles.