Side‐Effects of Downy Mildew Fungicides on the Incidence of Hop Powdery Mildew ( Sphaerotheca humuli )

SUMMARY In a trial on 10 acres (4 ha) of hops in 1972, three downy mildew fungicides were superimposed on to a routine dinocap schedule and compared for their effects on powdery mildew control. Both mildew diseases built up to fairly high levels between the last spray applications and harvest. Copper oxychloride was significantly superior to zineb in restricting development of powdery mildew in hop cones while propineb appeared to be only slightly inferior to copper. There were no differences between fungicides for control of downy mildew. Cone yield was significantly correlated with the amount of downy mildew, but not of powdery mildew, at harvest.