Epidemics of dwarf cashew powdery mildew as affected by flowering periods, clones and chemical control

Abstract

Epidemics of cashew powdery mildew are observed every year in most of the growing regions in Northeast Brazil. Currently, fungicide management is the main disease control strategy. This study aimed to compare powdery mildew epidemics according to the flowering periods in 2014 and 2019, in different dwarf cashew clones in 2018 and 2021, and with or without chemical control in 2016 and 2020. The disease severity data were used to calculate the variables area under the disease progress curve, final disease and onset of the epidemics, and the monomolecular linear model was used to calculate the initial disease incidence and disease progress rate. Regarding the flowering effect, it was found that, in 2014, the first flowering period stood out from the others for initial disease incidence, disease progress rate and area under the disease progress curve. In 2019, the third flowering period showed the lowest levels of initial disease incidence, area under the disease progress curve and final disease. As for the clones, ‘BRS 226’ stood out as the most resistant for most the disease variables in the two years of the study. The fungicide sprays had a significant effect and prevented the powdery mildew epidemics in the two years of the study. The powdery mildew epidemics showed to be more severe in the first flowering period and can be reduced by using chemical control and more resistant dwarf cashew clones.