In 1964 and 1965 trials were made with 6-azauracil (AzU) against powdery mildew and scab in an apple orchard at Kloetinge (Zeeland) and at Wageningen. The activity against scab was moderate, but against powdery mildew the results were better than those obtained with Karathane. The activity against mildew is ascribed to the systemic action of AzU, which protected shoots not hit by the spray, as well as those developing after the treatment. Sprays with AzU also reduced the overwintering of powdery mildew in the terminal buds. When concentrations of 100 and 50 ppm were used, the young shoots developing were often malformed, but even with lower concentrations, still active against mildew, the trees were not completely free of slight abnormalities.