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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #430172
Research Project: Development of Superior Hops and Resilient Hop Production Systems

Location: Forage Seed and Cereal Research Unit

Title: Constructing hop powdery mildew management programs that mitigate potential technical barriers to trade in the European Union

Author
item Gent, David
item RICHARDSON, BRIANA - Oregon State University
item MASSIE, STEPHEN - Washington Hop Commission

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2026
Publication Date: 3/25/2026
Citation: Gent, D.H., Richardson, B.J., Massie, S.T. 2026. Constructing hop powdery mildew management programs that mitigate potential technical barriers to trade in the European Union. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-11-25-0131-R.
DOI: https://doi.org/10.1094/PHYTOFR-11-25-0131-R

Interpretive Summary: This study looked for ways to control powdery mildew on hops without using quinoxyfen, a fungicide that may cause export issues because of differing pesticide limits between countries. Since about half of U.S. hops are exported—mainly to the European Union, which has stricter pesticide rules—growers need alternatives that meet EU standards. Over five years of field trials, researchers found that using certain fungicides like fluopyram + tebuconazole, trifloxystrobin, or BLAD at specific stages of hop growth and on regular schedules provided disease control just as effective as programs using quinoxyfen. The results show that hop growers can successfully manage powdery mildew and stay compliant with EU export rules by carefully selecting and timing fungicide applications.

Technical Abstract: A maximum residue limit (MRL) is a statutory limit of analyte concentration in or on food or feed. Maximum residue levels for a given pesticide may vary from country to country, potentially creating technical barriers to trade when these limits are incongruous. Approximately half of the hops produced in the U.S. are exported, with the EU being the most important market and also having the most restrictive MRL for numerous pesticides. Quinoxyfen historically has been central in fungicide programs management for hop powdery mildew (Podosphaera macularis), but there is concern that loss of a harmonized MRL for quinoxyfen may create a barrier to export. We conducted five years of field studies to develop guidance on fungicide programs that are EU-export-compliant, limit use of a single fungicide mode-of-action, and maximize efficacy without use of quinoxyfen. Plants that received fluopyram + tebuconazole during bloom and the juvenile stages of cone development had the least powdery mildew on cones, and were statistically comparable to disease levels when plants received quinoxyfen at the same timing. On leaves, the efficacy of MRL-compliant or exempt fungicides depended on the specific product and application interval. The most effective programs utilized trifloxystrobin on a 7-day or 10-day interval, or banda de Lupines albus doce (BLAD) on a 7-day interval, providing disease control comparable to a rotation of quinoxyfen and myclobutanil. These findings suggest that multiple programs offer alternatives to quinoxyfen, provided that specific fungicides are used at and after bloom and that application intervals are not excessively long.