Field experiments have been carried out in the past two years on the control of the potato late blight by dusting with a mixture of organic mercurial and hydrated lime. Started soon after the appearance of disease loci, dusting with the mixture of 1 part Seresan (2% ethyl mercuric chloride) and 9 parts hydrated lime or the same ratio of Ceresan (2.58% phenyl mercuric acetate) and hydrated lime, 5 times at 7 days interval, gave remarkable control of disease and increase in yield.