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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #418845
Research Project: Development of Superior Hops and Resilient Hop Production Systems

Location: Forage Seed and Cereal Research Unit

Title: Hop pathology

Author
item RADISEK, SEBASTJAN - Slovenian Institute Of Hop Research And Brewing
item Gent, David
item MILES, TIMOTHY - Michigan State University
item HARPER, SCOTT - Washington State University
item JAKSE, JERNEJ - University Of Ljubljana
item Zasada, Inga

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/29/2025
Publication Date: 2/1/2026
Citation: Radisek, S., Gent, D.H., Miles, T.D., Harper, S.J., Jakse, J., Zasada, I.A. 2026. Hop pathology. Book Chapter. ISBN 978-3-031-96605-7 PGS 121-194.

Interpretive Summary: This book chapter reviews and synthesizes information on priority diseases of hop, a culturally and economically important crop. We describe the causal organisms responsible for priority diseases, disease symptoms, the disease cycle and epidemiology, and management considerations. This chapter complements the other chapters in this book to provide an updated and authoritative introduction to the botany, cultivation, and importance of hop.

Technical Abstract: The cultivation of hops has always been challenged by the occurrence of diseases, which, if not properly controlled, can completely destroy a crop or even lead to plant death. Among the most important diseases of hop in the majority of hop-growing regions worldwide are hop downy mildew (Pseudoperonospora humuli Miyabe & Takah. G.W. Wilson), hop powdery mildew (Podosphaera macularis Wallr. U. Braun & Takam.), Verticillium wilt caused by Verticillium nonalfalfae Inderb., H. W. Platt, R. M. Bostock, R. M. Davis & K. V. Subbarao, and diseases caused by a complex of viruses and viroids. In addition to these, there are many more known pathogens on hop, representing a range of potential causes of economic damage. So far, over 30 different fungi, oomycetes, and bacteria, 12 viruses, 4 viroids, 12 plant-parasitic nematodes, and a phytoplasma from the group 16SrI-B have been described on hop. Among the known diseases are also some physiological disorders resulting from abiotic factors. Hop cultivation has faced significant epidemic outbreaks of diseases in the past, greatly impacting global hop trade. The transmission of the hop downy mildew pathogen from Japan to Europe and the USA in the years 1926-1936 caused devastating outbreaks, compelling growers to cultivate less susceptible varieties and implement annual protection using fungicides. Similarly, in 1997, an outbreak of powdery mildew in Washington State destroyed more than 800 hectares of hop, prompting growers in the Pacific Northwest production areas to cease production of a highly susceptible cultivar and implement strict control measures to limit damage. In Europe, the lethal form of Verticillium wilt, a soil-borne disease, has caused extensive plant dieback, severely affecting regions such as England, Slovenia, and Germany. More recently, epidemic caused by viroids have caused substantial damage to hop production. A newly discovered viroid on hop, citrus bark cracking viroid (CBCVd), has severely affected more than 500 hectares in Slovenia since 2010, and its recent introduction to Germany has already affected several farms. Since 2004, the USA has reported the progression and spreading of hop stunt viroid, significantly reducing growth and yield in several important varieties. Continuous adaptation of pathogens to new hosts, the monoculture of hop cultivation, the introduction of contaminated planting material from other regions, the expansion of production into new areas, and climate change are, and will continue to be, risk factors for the emergence or re-emergence of disease. Reports from the last three decades show an increasing discovery of new pathogens of hop and the detection of new pathotypes and races, presenting future challenges in hop production. New detection methods for pathogens, epidemiological studies, resistance breeding, and new approaches in integrated pest management are crucial for future sustainable disease control in hop production. This chapter is therefore dedicated to reviewing diseases on hop, providing descriptions of the pathogens, disease symptoms, and management practices.