Constructing Hop Powdery Mildew Management Programs That Mitigate Potential Technical Barriers to Trade in the European Union

A maximum residue limit (MRL) is a statutory limit of analyte concentration for a food or feed. An MRL 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 for management offor hop powdery mildew (Podosphaera macularis), but there is concern that loss of a harmonized MRL for quinoxyfen (currently 3 ppm) 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 offer alternatives to quinoxyfen when provided specific fungicides are used at and after bloom and that application intervals are appropriately matched for each fungicide.