Persistence and identification of downy mildew Pseudoperonospora humuli (Miy. and Tak.) Wilson in hop rootstocks



Evidence is presented which suggests that Pseudoperonospora humuli persists, in a high proportion of infected hop rootstocks, for at least 4 years in this country, and the grubbing of these rootstocks is recommended. Methods are described for diagnosis of downy mildew during the dormant season in the field and in the laboratory.