Management Strategies for Hop Downy Mildew Utilizing Fungicides and Host Resistance

Abstract

Hop (Humulus lupulus L.) is an herbaceous perennial plant species that is native to the Northern hemisphere. The hop inflorescences are utilized during the production of beer. Commercial production of hops requires the use of fungicides and host resistance to retain high overall yields and quality characteristics that brewers are satisfied with. The primary objectives of this research were to determine effective fungicidal compounds that can be used to control hop downy mildew (caused by Pseudoperonospora humuli (Miy. et Takah.) Wils.) and to collect and characterize a panel of 112 diverse H. lupulus accessions for resistance to P. humuli. Results from field fungicide trials indicate that significant interactions exist between cultivars, environments, and fungicidal compounds with regards to disease severity. With regards to host resistance, H. lupulus var. lupuloides E. Small accessions originating from the United States were highly-resistant to P. humuli compared to their North American counterparts H. lupulus var. neomexicanus Nelson & Cockerell or H. lupulus var. pubescens E. Small. Comparisons of H. lupulus var. lupuloides from Canada indicated that accessions from the United States were significantly more resistant to P. humuli, but not significantly different from H. lupulus var. lupulus accessions originating from Kazakhstan. These results indicate that control of hop downy mildew can be accomplished through use of resistant cultivars, fungicidal compounds, and selection of proper environments for cultivation. Additionally, utilization of H. lupulus var. lupuloides will increase the diversity of resistant sources to hop downy mildew in the development of new cultivars.