The effect of dusting elemental sulphur (S) as a fungicide for controlling powdery mildew (Oidium anarcadii) disease in cashew (Anacardium occidentale L.) upon soil fertility was studied in two agro-ecological zones (AEZ), termed C2 and E5. Annual S dusting decreased the pH of topsoil by up to 0. 7 units over a period of four years dusting, reducing pH values to less than the critical 5.5 level in some areas. At most sites a decrease in pH was associated with the loss of major soil macronutrient elements from the topsoil due to leaching. An increase in Al saturation to toxic levels also occurred, particularly in A C2. Preliminary data showed that annual crop performance was also negatively affected by the increased soil acidity in some soils. From these results it was concluded that the annual application of S dust to control powdery mildew disease is not environmentally sustainable and alternative control strategies are needed with less damaging effects on environment.