Late season fungicide applications for hop powdery mildew have llttle effect on disease suppression and cone quality metrics in the cultivar Nugget

Authors: Gent, David; RICHARDSON, BRIANA - Oregon State University; MASSIE, STEPHEN - Washington Hop Commission

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2026
Publication Date: 3/31/2026
Citation: Gent, D.H., Richardson, B.J., Massie, S.T. 2026. Late season fungicide applications for hop powdery mildew have llttle effect on disease suppression and cone quality metrics in the cultivar Nugget. Plant Health Progress. https://doi.org/10.1094/PHP-12-25-0270-BR.
DOI: https://doi.org/10.1094/PHP-12-25-0270-BR

Interpretive Summary: We conducted three years of field studies in Oregon to understand if or when late-season control measures for powdery mildew can be safely omitted for the cultivar Nugget. This research question was of interest because this cultivar was formerly resistant to powdery mildew, but growers now must manage the disease and need guidance on best management practices. We found that making additional fungicide applications after late July or early August did not improve powdery mildew control on cones or enhance crop quality metrics. This suggests that Oregon producers of Nugget hops can likely omit late-season fungicide applications without compromising disease control or crop quality.

Technical Abstract: Powdery of hop, caused by Podosphaera macularis, is managed in large part on susceptible cultivars by fungicide applications applied through the growing season to minimize disease on the cones, which are the harvested product. The impact of fungicide applications made after the juvenile stages of cone development are reported to have small or nondeductible effects on certain hop cultivars in certain environments. However, there is no information on the cultivar Nugget, a historically important cultivar in Oregon hop production regions, because until 2014 this cultivar was unaffected by powdery mildew due to R-gene mediate resistance. However, Nugget now routinely develops powdery mildew because virulent races of P. macularis are widespread in the Pacific Northwest. To guide Oregon growers’ management decisions on the cultivar Nugget, we conducted three years of field studies to quantify the impact and value of late season fungicide applications on powdery mildew control on cones. Making one, two, or three additional fungicide applications after late July to early August did not improve control of powdery mildew, alpha-acids content, the hop storage index, or cone color relative to ceasing applications at these times. This finding should give confidence to Oregon producers of Nugget that late-season fungicide applications for powdery mildew can be omitted after the critical periods of juvenile susceptible in cones without compromising disease control or crop quality.