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The experimental area was installed in a commercial orchard in Nilo Coelho, Petrolina, Brazil to evaluate the efficiency of chemical and biological agents in the control of Erysiphe polygoni D. C. Sin., causal agent of powdery mildew in mango 'Tommy Atkins' trees. The study was conducted in the second semester of 2001, under 22degreesC to 30degreesC, and 45 to 82 RH. Nine treatments were evaluated: seven chemical compounds, a biological agent formulation, and an absolute control. The formulation DE 975 + Fenarimol was applied at the beginning of flower development. Its efficiency was compared to a single application and 4 ten day-interval applications of an standard product (Folicur 200 CE - 100ml/100L of water. The results showed that the treatment - DE 975 + Fenarimol 50ml/150L of water, was the most efficient for the control of powdery mildew reaching 0% of infection in whole cycle of the culture.