Hop powdery mildew, caused by Podosphaera macularis Braun & Takamatsu (formerly Sphaerotheca macularis (Wallr. :Fr.) Lind, syn. S. humuli (DC.)Burrill) was not observed in Pacific Northwest hop yards until 1997, when it was discovered in Washington. Within one year, it had spread to Oregon and Idaho. This emerging disease caused...
