Field experiments were conducted during the vegetative season of April–October 2008 and 2009 and fruiting season of October–April 2008–09 and 2009–10, to study the efficacy of Milastin K, a formulation containing Bacillus subtilis (KTBS), for the control of powdery mildew on grapes. Five to six sprays of Milastin K @ 1.0 ml l–1 (1.0 l ha–1), from 30–119 days after pruning at 7–22 days interval (depending on weather based disease risk) could effectively control powdery mildew on leaves and bunches in grapes and increase yield. The untreated control recorded PDI in the range of 4.00–82.13 during different seasons, Milastin K treatment significantly reduced PDI to 1.62–20.69. Under low to moderate disease pressure conditions, the efficacy of Milastin K in controlling powdery mildew was on par with sulphur 80 WG @ 2.0g l–1. Under high disease pressure condition, Milastin K was not so effective when used alone, but was effective when used in integration with fungicide sprays. Harvestable yield of 4.55 kg per vine was recorded in Milastin K while there was nil yield in untreated control. There was no phytotoxic effect of Milastin K on vines when it was sprayed at a dose up to 2.0 ml l–1.