Here you will find curated research articles about sustainable hop growing. This site aims to provide growers, researchers, and industry partners with vetted information to help them make sustainable choices in their hop farming practices.
Research on this site has been carefully selected by Hop Growers of America (HGA), a trade association that supports and promotes hop growers throughout the United States. You can learn more about HGA on their website, usahops.org.
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Economic Sustainability
Published August, 2012
According to USDA report/data (USDA/NASS) U.S. hop prices have changed dramatically in the last 2 decades. For example, prices increased by 35% (20% in real terms) from 2007-2008 and decreased by 11% (20% in real terms) from 2009-2010.
Environmental SustainabilityPublished 2016
Hop petioles were excluded from this study because they were too inconsistent as compared to leaves plus petioles collected at 5 ½ feet above ground and leaves plus petioles collected 1 foot below the wire.
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Environmental SustainabilityPublished 2015
Results of 28 field trials conducted over a 12-year period investigating management of hop powdery mildew caused by Podosphaera macularis were quantitatively summarized by meta-analysis to compare product efficacy and use patterns by mode of action as defined by Fungicide Resistance Action Committee (FRAC) groups. Availability of original observations enabled individual participant data meta-analysis. Differences in control of powdery mildew on leaves and cones were apparent among fungicide FRAC groups when individual products were evaluated over the course of a growing season. FRAC groups 13, 3, and U13 provided the most efficacious control of powdery mildew on leaves. Percent disease control on cones was influenced by midseason foliar disease and fungicide mode-of-action. FRAC 13 provided significantly better disease control on cones than all other groups except U13, 3, and premixes of 7 with 11.
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Categories: Pests
Environmental SustainabilityPublished March, 2016
Podosphaera macularis, the casual agent of hop powdery mildew, is a recurrent threat to hops in the Pacific Northwest because of the potential to reduce cone yield and quality. Early-season pruning is a common practice in hop production for horticulture reasons. Studies were conducted over a 3-year period in a commercial hop yard to quantify the effect of pruning method and timing on disease development, yield, and cone quality factors. A 4-week delay in pruning reduced the incidence of leaves with powdery mildew from 46% to 10% and cones from 9 to 1%, with the specific effect being season dependent.
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Categories: Pests
Environmental Sustainability
Published April, 2025
Trials were established in two commercial hop yards varying either the dose (cv. ‘Tomahawk’) or timing (cv. ‘Simcoe’) of nitrogen fertilizer applications and measuring the subsequent changes in levels of powdery mildew. Studies evaluating nitrogen dose were conducted near Moxee, Washington during 2015 and 2016. Three nitrogen rates, 90 kg/ha, 179 kg/ha, and 269 kg/ha, were evaluated. The hop yard was planted with 4.3 m between rows and 1 m between each hill (plant) within the rows, allowing for about 2,200 hills per ha under a 5.5 m trellis. Thirty-four kg/ha (2015) or 86 kg/ha (2016) of nitrogen was banded in late winter to early spring across the whole field. The yard was irrigated by surface drip irrigation and the remaining nitrogen necessary to reach the overall desired rates was injected through the drip bi-weekly as urea ammonium nitrate (32-0-0) or calcium ammonium nitrate (21-0-0).
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2020
Trials were conducted in a short trellis hop yard (cv. Galena) near Granger, Washington. A plot consisted of nine plants in a single row, with plants separated by 3 ft within the row and 10 ft between rows, and strung with a single string per plant under a 10 ft trellis. The yard was managed to commercial standards by the hosting farm, minus application of any fungicides suppressive to powdery mildew. Plots were arranged in a randomized complete block design with six replicates. The first two applications were directed to both sides of plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles at approximately 30 psi pressure. Subsequent applications were directed to both sides of the plants from the base to the top using a Cifarelli M1200 backpack mist sprayer. In total, eight applications were made on a two-week interval beginning 15 May. Application volume was equivalent of 40 gal/A for the first application, 60 gal/A for the second, and 120 gal/A thereafter.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2019
Trials were conducted in a short trellis hop yard (cv. Galena) near Granger, Washington. A plot consisted of nine plants in a single row, with plants separated by 3 ft within the row and 10 ft between rows, and strung with a single string per plant under a 10 ft trellis. The yard was managed to commercial standards by the hosting farm, minus application of any fungicides suppressive to powdery mildew. Plots were arranged in a randomized complete block design with six replicates. Fungicides were directed to both sides of the plants from the base to the top using a Cifarelli M1200 backpack mist blower. Eight applications were made on a 2-wk interval beginning 22 May. Application volume was equivalent to 40 gal/A for the first application, 60 gal/A for the second, and 120 gal/A thereafter.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2019
A trial was conducted in a commercial hop yard (cv. Nugget) near Hubbard, Oregon, to evaluate various fungicides for management of downy mildew. A plot consisted of 7 plants in a single row, with plants separated by 7.5 ft within a row and 15 ft between rows. Plots were arranged in a randomized complete block design with five replications. Fungicides were directed to both sides of plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles. Applications were made in a volume equivalent to 35 gal/A at a pressure of approximately 30 psi pressure. Four applications were made on a 14-d interval with applications occurring on 10 Apr, 24 April, 8 May and 23 May. Levels of downy mildew were assessed by counting the number of shoots with signs and symptoms of systemic downy mildew on each plant.
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Categories: Efficacy Trials
Environmental Sustainability
Published April, 2025
Thirty three hop genotypes were screened for their reaction to multiple isolates of P. macularis.. Currently there are three strains of P. macularis described in the Pacific Northwestern U.S., specifically, strains virulent on plants possessing R6 (R6-virulent), strains lacking R6-virulence (non-R6-virulent), and strains adapted to the quantitative resistance found in the cultivar Cascade (Cascade-adapted). Rhizomes were collected in the winter of 2015 from a USDA breeding yard in Corvallis, Oregon or from a private breeding program in Yakima, Washington, potted, and grown in a greenhouse free of powdery mildew. The greenhouse was maintained at 20 to 25°C with a 14 hour photoperiod.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2019
Trials were conducted in a short trellis hop yard (cv. Galena) near Granger, Washington. A plot consisted of nine plants in a single row, with plants separated by 3 ft within the row and 10 ft between rows, and strung with a single string per plant under a 10 ft trellis. The yard was managed to commercial standards by the hosting farm, minus application of any fungicides suppressive to powdery mildew. Plots were arranged in a randomized complete block design with six replicates. The first two applications were directed to both sides of plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles at approximately 30 psi pressure. Subsequent applications were directed to both sides of the plants from the base to the top using a Cifarelli M1200 backpack mist sprayer. For treatments applied via a simulated chemigation through drip irrigation, applications were made under each irrigation emitters in a plot using a syringe to apply 10 ml of a dilute solution corresponding to the equivalent per acre rate. For these applications, the soil was pre-wetted by irrigation for at least an hour before the application and the fungicide was incorporated by irrigation for an hour after application. In total, eight applications were made on a two-week interval beginning 15 May.
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Categories: Efficacy Trials
Environmental Sustainability
Published 2016
A trial was conducted in a commercial hop yard (cv. Nugget) near Woodburn, Oregon. A plot consisted of 8 plants in a single row, with plants separated by 7.5 ft within a row, 15 ft between rows, and strung with four strings per plant under an 18 ft trellis. Plots were arranged in a randomized complete block design with four replications. Fungicides were directed to both sides of the bases of the plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles in an application equivalent to 35 gal/A at a pressure of approximately 30 psi pressure. Five weekly applications were made on 21, 29 Apr, and 5, 13, and 20 May. Levels of downy mildew were assessed by counting the number of basal shoots with characteristic signs and symptoms of systemic downy mildew on each plant. Disease evaluations were conducted just before the first fungicide application was applied and every two weeks thereafter until mid-Jun. Data were log-transformed and analyzed in a mixed effect model with random factors for block and subsamples (plants within blocks). The factor for ‘block’ was removed from models on 21 Apr and 5 May because the covariance parameter estimates were 0.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2020
A trial was conducted in a commercial hop yard (cv. Nugget) near Hubbard, Oregon. A plot consisted of 7 plants in a single row, with plants separated by 7.5 ft within a row, 15 ft between rows. Plants were not strung. Plots were arranged in a randomized complete block design with five replications. Fungicides were directed to both sides of the plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles in an application equivalent to 35 gal/A at a pressure of approximately 30 psi. For drench treatments, fungicides were applied as a concentrated band only on the first application date. For these applications, the fungicide was incorporated by applying approximately 0.25” of water by overhead irrigation over the entire field the following day.
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Categories: Efficacy Trials
Environmental Sustainability
Published 2020
Trials were conducted in a short trellis hop yard (cv. Galena) near Granger, Washington. A plot consisted of nine plants in a single row, with plants separated by 3 ft within the row and 10 ft between rows, and strung with a single string per plant under a 10 ft trellis. The yard was managed to commercial standards by the hosting farm, minus application of any fungicides suppressive to powdery mildew. Plots were arranged in a randomized complete block design with six replicates. The first two applications were directed to both sides of plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles at approximately 30 psi. Subsequent applications were directed to both sides of the plants from the base to the top using a Cifarelli M1200 backpack mist sprayer. In total, eight applications were made on a two-week interval beginning 23 May.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2018
Trials were conducted in a research hop yard (cv. Zeus) located at the Washington State University Irrigated Agriculture Research and Extension Center near Prosser, WA. Each plot consisted of nine plants in a single row with 3-ft plant spacing within the row and 10 ft between rows. Plants were not strung. The yard was irrigated by overhead sprinklers for approximately four hours once per week. Plots were arranged in a randomized complete block design with four replicates. Fungicides were directed to both sides of plants using a CO2-pressurized backpack sprayer and a 24 in. boom equipped with two 8002 V5 nozzles. Applications were made in a volume equivalent to 35 gal/A at a pressure of approximately 30 psi. Four applications were made on a 7-day interval beginning on 1 Jun. Levels of downy mildew were assessed by counting the number of shoots with signs and symptoms of systemic downy mildew on each plant. Disease evaluations were conducted just before the first application was applied and then two, four, and six weeks later. On 7 Jul, differences in powdery mildew were noted between plots receiving different fungicide treatments.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2018
Trials were conducted in a commercial hop yard (cv. Zeus) near Toppenish, Washington. A plot consisted of nine plants in a single row, with plants separated by 3.5 ft within the row and 14 ft between rows, and strung with a single string per plant under an 18-ft trellis. The yard was managed to commercial standards by the hosting farm, except for the application of fungicides with any activity on powdery mildew. Plots were arranged in a randomized complete block design with four replicates. Fungicides were directed to both sides of the plants from the base to the top using a Cifarelli 1200 backpack mist blower. Eight applications were made on a two-week interval beginning on 23 May. Application volume was equivalent of 40 gal/A for the first application, 60 gal/A for the second, 90 gal/A for the third, and 120 gal/A thereafter. The incidence of leaves with powdery mildew was assessed by sampling 20 leaves (10 each from the west and east sides of the plant) from each of the middle seven plants in each plot. Foliar disease evaluations were conducted every two weeks from 29 May to 8 Aug. On 11 Sep, three lateral branches were arbitrarily selected from each plant.
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Categories: Efficacy Trials
Environmental SustainabilityPublished 2018
Trials were conducted in a commercial hop yard (cv. Zeus) near Toppenish, Washington. A plot consisted of nine plants in a single row, with plants separated by 3.5 ft within the row and 14 ft between rows, and strung with a single string per plant under an 18-ft trellis. The yard was managed to commercial standards by the hosting farm, minus application of any fungicides suppressive to powdery mildew. Plots were arranged in a randomized complete block design with four replicates. Fungicides were directed to both sides of the plants from the base to the top using a Cifarelli 1200 backpack mist blower. For treatments applied via a simulated chemigation through drip irrigation, applications were made under the first 18-20 irrigation emitters in plots using a syringe to apply 50 ml of a dilute solution corresponding to the equivalent per acre rate. For these applications, the soil was pre-wetted for at least an hour before the application and the fungicide was incorporated by irrigation for an hour after application.
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Categories: Efficacy Trials
Environmental Sustainability
Published November, 2015
RNA sequencing (RNA-seq) and genotyping-by-sequencing (GBS) were used for single nucleotide polymorphism (SNP) identification from two economically important obligate plant pathogens, Pseudoperonospora cubensis and P. humuli. Twenty isolates of P. cubensis and 19 isolates of P. humuli were genotyped using RNA-seq and GBS. Principle components analysis (PCA) of each data set showed genetic separation between the two species. Additionally, results supported previous findings that P. cubensis isolates from squash are genetically distinct from cucumber and cantaloupe isolates. A PCA-based procedure was used to identify SNPs correlated with the separation of the two species, with 994 and 4,231 PCA-correlated SNPs found within the RNA-seq and GBS data, respectively. The corresponding unigenes (n = 800) containing these potential species-specific SNPs were then annotated and 135 putative pathogenicity genes, including 3 effectors, were identified. The characterization of genes containing SNPs differentiating these two closely related downy mildew species may contribute to the development of improved detection and diagnosis strategies and improve our understanding of host specificity pathways.
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Categories: Pests
Environmental SustainabilityPublished February, 2020
Powdery mildew, caused by Podosphaera macularis, is one of the most important diseases of hop. The disease was first reported in the Pacific Northwestern United States, the primary hop-growing region in this country, in the mid-1990s. More recently, the disease has reemerged in newly planted hopyards of the eastern United States, as hop production has expanded to meet demands of local craft brewers. The spread of strains virulent on previously resistant cultivars, the paucity of available fungicides, and the potential introduction of the MAT1-2 mating type to the western United States, all threaten sustainability of hop production. We sequenced the transcriptome of 104 isolates of P. macularis collected throughout the western United States, eastern United States, and Europe to quantify genetic diversity of pathogen populations and elucidate the possible origins of pathogen populations in the western United States.
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Categories: Pests
Environmental Sustainability
Published June, 2019
Pseudoperonospora humuli is the causal agent of downy mildew of hop, one of the most important diseases of this plant and a limiting factor for production of susceptible cultivars in certain environments. The degree of genetic diversity and population differentiation within and among P. humuli populations at multiple spatial scales was quantified using genotyping-by-sequencing to test the hypothesis that populations of P. humuli have limited genetic diversity but are differentiated at the scale of individual hop yards. Hierarchical sampling was conducted to collect= isolates from three hop yards in Oregon, plants within these yards, and infected shoots within heavily diseased plants. Additional isolates also were collected broadly from other geographic regions and from the two previously described clades of the sister species, P. cubensis. Genotyping of these 240 isolates produced a final quality-filtered data set of 216 isolates possessing 25,227 variants. Plots of G’ST values indicated that the majority of variants had G’ST values near 0 and were scattered randomly across contig positions. However, there was a subset of variants that were highly differentiated (G’ST > 0.3) and reproducible when genotyped independently. Within P. humuli, there was evidence of genetic differentiation at the level of hop yards and plants within yards; 19.8% of the genetic variance was associated with differences among yards and 20.3% of the variance was associated with plants within the yard.
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Categories: Pests
Environmental SustainabilityPublished February, 2019
Dispersal is a fundamental aspect of epidemic development at multiple spatial scales, including those that extend beyond the borders of individual fields and to the landscape level. In this research, we used the powdery mildew of the hop pathosystem (caused by Podosphaera macularis) to formulate a model of pathogen dispersal during spring (May to June) and early summer (June to July) at the intermediate scale between synoptic weather systems and microclimate (mesoscale) based on a census of commercial hop yards during 2014 to 2017 in a production region in western Oregon. This pathosystem is characterized by a low level of overwintering of the pathogen as a result of absence of the ascigerious stage of the fungus and consequent annual cycles of localized survival via bud perennation and pathogen spread by windborne dispersal. An individual hop yard was considered a node in the model, whose disease status in a given month was expressed as a nonlinear function of disease incidence in the preceding month, susceptibility to two races of the fungus, and disease spread from other nodes as influenced by their disease incidence, area, distance away, and wind run and direction in the preceding month.
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Categories: Pests
Environmental Sustainability
Published April, 2021
Hop powdery mildew, caused by the ascomycete fungus Podosphaera macularis, is a consistent threat to sustainable hop production. The pathogen utilizes two reproductive strategies for overwintering and perennation: (i) asexual vegetative hyphae on dormant buds that emerge the following season as infected shoots; and (ii) sexual ascocarps (chasmothecia), which are discharged during spring rain events. We demonstrate that P. macularis chasmothecia, in the absence of any asexual P. macularis growth forms, are a viable overwintering source capable of causing early season infection two to three orders of magnitude greater than that reported for perennation via asexual growth. Two epidemiological models were defined that describe (i) temperature-driven maturation of P. macularis chasmothecia; and (ii) ascosporic discharge in response to duration of leaf wetness and prevailing temperatures. P. macularis ascospores were confirmed to be infectious at temperatures ranging from 5 to 20C. The organism’s chasmothecia were also found to adhere tightly to the host tissue on which they formed, suggesting that these structures likely overwinter wherever hop tissue senesces within a hop yard. These observations suggest that existing early season disease management practices are especially crucial to controlling hop powdery mildew in the presence of P. macularis chasmothecia. Furthermore, these insights provide a baseline for the validation of weatherdriven models describing maturation and release of P. macularis ascospores, models that can eventually be incorporated into hop disease management programs.
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Categories: Pests
Environmental SustainabilityPublished March, 2019
Pseudoperonospora humuli is an obligate oomycete pathogen of hop (Humulus lupulus) that causes downy mildew, an important disease in most production regions in the Northern Hemisphere. The pathogen can cause a systemic infection in hop, overwinter in the root system, and infect propagation material. Substantial yield loss may occur owing to P. humuli infection of strobiles (seed cones), shoots, and cone-bearing branches. Fungicide application and cultural practices are the primary methods to manage hop downy mildew. However, effective, sustainable, and cost-effective management of downy mildew can be improved by developing early detection systems to inform on disease risk and timely fungicide application. However, no species-specific diagnostic assays or genomic resources are available for P. humuli.
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Categories: Pests
Environmental SustainabilityPublished September, 2020
Obligately biotrophic plant pathogens pose challenges in population genetic studies due to their genomic complexities and elaborate culturing requirements with limited biomass. Hop powdery mildew (Podosphaera macularis) is an obligately biotrophic ascomycete that threatens sustainable hop production. P. macularis populations of the Pacific Northwest (PNW) United States differ from those of the Midwest and Northeastern United States, lacking one of two mating types needed for sexual recombination and harboring two strains that are differentially aggressive on the cultivar Cascade and able to overcome the Humulus lupulus R-gene R6 (V6), respectively. To develop a high-throughput marker platform for tracking the flow of genotypes across the United States and internationally, we used an existing transcriptome of diverse P. macularis isolates to design a multiplex of 54 amplicon sequencing markers, validated across a panel of 391 U.S.
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Categories: Pests
Environmental SustainabilityPublished May, 2019
Scaling of management efforts beyond the boundaries of individual farms may require that individuals act collectively. Such approaches have been suggested several times in plant pathology contexts but rarely have been implemented, in part because the institutional structures that enable successful collective action are poorly understood. In this research, we conducted in-depth interviews with hop producers in Oregon and Washington State to identify their motivations for and barriers to collective action regarding communication of disease levels, coordination of management practices, and sharing of best management practices and other data for powdery mildew (caused by Podosphaera macularis). Growers were generally open to and engaged in communication with neighbors and others on disease status in their hop yards and some evidence of higher levels of information sharing on management practices was found.
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Categories: Pests
Environmental SustainabilityPublished March, 2016
Hop downy mildew (caused by Pseudoperonospora humuli) is a yieldlimiting disease in many hop-production regions of the world. In this research, 110 cultivars that are or were widely grown in the United States, Europe, or Australasia were evaluated in western Oregon over three years for their reaction to the shoot infection phase of downy mildew and vigor. There was a large range of downy mildew susceptibility and vigor amongst commercial cultivars, with some cultivars possessing a very high level of resistance. Overall, however, disease resistance and vigor were significantly greater in cultivars originating from Europe than those originating from the United States, Japan, and Australia/New Zealand. Amongst a subset of 79 cultivars, vigor was negatively correlated with levels, in cones, of cohumulone, a chemical constitute of bittering acids typically found in germplasm derived from North America. The generally poor vigor observed in cultivars derived outside of Europe likely is indicative of a lack of tolerance to the crown infection phase of the disease. Thus, the best sources of downy mildew resistance seems to be found in cultivars from the United Kingdom and continental Europe, and such cultivars are typically lower yielding and lack distinctive aroma and flavor characteristics presently desired by craft brewers. Introgression of downy mildew resistance into North American germplasm with high yield and desirable brewing characteristics is needed.
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Categories: Pests
Environmental SustainabilityPublished February, 2021
Powdery mildew, caused by Podosphaera macularis, is a destructive disease of hop (Humulus lupulus) (Mahaffee et al. 2009). Host resistance is an efficient means of managing the disease, and breeding efforts have produced multiple cultivars with resistance to powdery mildew (Royle 1978). One such cultivar is ‘Strata’, which was developed by Oregon State University and produced on 309 ha in Oregon in 2020 (National Agricultural Statistics Service 2020). The 2017 patent application for Strata stated the plant was resistant to powdery mildew based on an initial greenhouse screening and 8 years of observations at three locations in Oregon (Townsend 2019). The genetic basis of the reported powdery mildew resistance in Strata is unknown.
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Categories: Pests
Environmental SustainabilityPublished April, 2020
The commercial host of downy mildew is hop (Humulus lupulus L.). Hop, a perennial dioecious plant belonging to the Cannabaceae family (Natsume et al. 2015), is an indispensable ingredient in beer due to its contribution to bittering, flavor, aroma, preservation, and product stability. The female hop inflorescence, often referred to as a cone but botanically a strobile, is the economically important part of the plant. The cones are made of petallike bracts and bracteoles that harbor lupulin glands, the main source of brewing value in hops (Almauger et al. 2014).
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Categories: Pests
Environmental Sustainability
Published May, 2021
In Oregon, hemp (Cannabis sativa) production has increased substantially after cultivation was legalized in the 2014 and 2018 Farm Bills. Both hemp and hop (Humulus lupulus), two agriculturally important crops in the Pacific Northwest, are affected by powdery mildew diseases. Golovinomyces spp. have been reported to cause hemp powdery mildew in Canada (Pepin et al. 2018) and the United States (Farinas and Peduto Hand 2020; Szarka et al. 2019; Weldon et al. 2020), including Oregon (Wiseman et al. 2021). More recently, Podosphaera macularis was found to colonize hemp following inoculations under controlled conditions (Weldon et al. 2020) and has been reported to be naturally occurring in a hemp field in British Columbia, Canada (Z. K. Punja, personal communication). P. macularis has been a problem on hop in the Pacific Northwest since the 1990s, when the fungus was introduced into the region; however, this species has not been widely considered as a concern for hemp growers.
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Categories: Pests
Environmental SustainabilityPublished June, 2021
The recent surge in the craft brewing market has renewed hop production throughout much of the Midwestern and Eastern United States, adding an element of locally sourced hops for use by regional breweries. All the while, the U.S. Pacific Northwest remains the stronghold of U.S. hop production, supplying hops for breweries worldwide. As the industry has evolved, so too have the challenges associated with managing the major pathogens of hop, especially with respect to Podosphaera macularis, the causal agent of hop powdery mildew.
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Categories: Pests
Environmental SustainabilityPublished January, 2017
The hop cultivar Cascade has been grown in the Pacific Northwestern U.S. and elsewhere with minimal input for management of powdery mildew (Podosphaera macularis) for nearly 15 years due to the putatively quantitative resistance in this cultivar. While partial resistance is generally thought to be more durable than qualitative resistance, in 2012, powdert mildew was reported on Cascade in Washington State.
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Categories: Pests
Environmental SustainabilityPublished February, 2016
Host resistance, both quantitative and qualitative, is the preferred long-term approach for disease management in many pathosystems, including powdery mildew of hop (Podosphaera macularis). In 2012, an epidemic of powdery mildew occurred in Washington and Idaho on previously resistant cultivars whose resistance was putatively based on the gene designated R6. In 2013, isolates capable of causing severe disease on cultivars with R6-based resistance were confirmed in Oregon and became widespread during 2014. Surveys of commercial hop yards during 2012 to 2014 documented that powdery mildew is now widespread on cultivars possessing R6 resistance in Washington and Oregon, and the incidence of disease is progressively increasing. Pathogenic fitness, race, and mating type of R6-virulent isolates were compared with isolates of P. macularis lacking R6 virulence.
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Categories: Pests
Environmental Sustainability
Published 2021
Oregon is one of the largest producers of hemp in the United States with 25,900 ha of hemp licensed to growers in 2019, a five-fold increase over the previous year. Industrial hemp has a wide range of uses including textiles to nutritional supplements; in Oregon, hemp has become one of the most economically promising crops and is mainly cultivated for cannabidiol (CBD) production. Between 2018 and 2019, multiple independent greenhouse growers in western Oregon reported powdery mildew-like signs and symptoms on leaves and buds of several Cannabis sativa cultivars, including ‘Cherry Wine’.
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Categories: Pests
Environmental SustainabilityPublished February, 2021
The ability to detect and quantify aerially dispersed plant pathogens is essential for developing effective disease control measures and epidemiological models that optimize the timing for control. There is an acute need for managing the downy mildew pathogens infecting cucurbits and hop incited by members of the genus Pseudoperonospora (Pseudoperonospora cubensis clade 1 and 2 isolates and Pseudoperonospora humuli, respectively). A highly specific multiplex TaqMan quantitative polymerase chain reaction (PCR) assay targeting unique sequences in the pathogens’ mitochondrial genomes was developed that enables detection of all three taxa in a single multiplexed amplification.
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Categories: Pests
Environmental SustainabilityPublished December, 2019
Phosphonate (phosphite; HPO3 −2) is fungicidal against oomycetes and certain other organisms. The Fungicide Resistance Action Committee has deemed phosphonate to be at low risk of resistance development, and reduced sensitivity to phosphonate has been reported only occasionally in plant pathogens. Reduced sensitivity to the fungicide fosetyl-Al was documented in the hop downy mildew pathogen, Pseudoperonospora humuli, in the early 2000s, but disease caused by insensitive isolates could still be managed commercially if the fungicide rate was doubled from 2.24 to 4.48 kg/ha.
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Categories: Pests
Environmental SustainabilityPublished January, 2018
In the Pacific Northwestern United States, the hop powdery mildew fungus, Podosphaera macularis, survives overwintering periods in association with living host tissue because the ascigerious stage of the pathogen is not known to occur in this region. Field experiments were conducted over a 5-year period to describe the overwintering process associated with crown bud infection and persistence of P. macularis. Surface crown buds increased in abundance and size beginning in early July and continuing until mid-September.
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Categories: Pests
Environmental Sustainability
Published January, 2016
Canopy management is an important aspect of control of powdery mildew diseases and may influence the intensity of fungicide applications required to suppress disease. In hop, powdery mildew (caused by Podosphaera macularis) is most damaging to cones when infection occurs during bloom and the juvenile stages of cone development. Experiments were conducted over 3 years to evaluate whether fungicide applications could be ceased after the most susceptible stages of cone development (late July) without unduly affecting crop yield and quality when disease pressure was moderated with varying levels of basal foliage removal
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Categories: Pests
Environmental SustainabilityPublished January, 2015
Optimum timing and use of fungicides for disease control are improved by an understanding of the characteristics of fungicide physical mode of action. Greenhouse and field experiments were conducted to quantify and model the duration of pre- and postinfection activity of fungicides most commonly used for control of hop downy mildew (caused by Pseudoperonospora humuli). In greenhouse experiments, control of downy mildew on leaves was similar among fungicides tested when applied preventatively but varied depending on both the fungicide and the timing of application postinfection.
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Categories: Pests
Environmental SustainabilityPublished September, 2020
Hop powdery mildew (caused by Podosphaera macularis) was confirmed in the Pacific Northwest in 1996. Before 2012, the most common race of P. macularis was able to infect plants that possessed powdery mildew resistance based on the R-genes Rb, R3, and R5. After 2012, two additional races of P. macularis were discovered that can overcome the resistance gene R6 and the partial resistance found in the cultivar Cascade. These three races now occur throughout the region, which can complicate management and research efforts because of uncertainty on which race(s) may be present in the region and able to infect susceptible hop genotypes.
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Categories: Pests
Environmental Sustainability
Published March, 2021
Pseudoperonospora humuli is an obligate biotrophic oomycete that causes downy mildew, one of the most devastating diseases of cultivated hop, Humulus lupulus. Downy mildew occurs in all production areas of the crop in the Northern Hemisphere and Argentina. The pathogen overwinters in hop crowns and roots, and causes considerable crop loss. Downy mildew is managed by sanitation practices, planting of resistant cultivars, and fungicide applications. However, the scarcity of sources of host resistance and fungicide resistance in pathogen populations complicates disease management.
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Categories: Pests
Environmental SustainabilityPublished March, 2015
Knowledge of processes leading to crop damage is central to devising rational approaches to disease management. Multiple experiments established that infection of hop cones by Podosphaera macularis was most severe if inoculation occurred within 15 to 21 days after bloom. This period of infection was associated with the most pronounced reductions in alpha acids, cone color, and accelerated maturation of cones. Susceptibility of cones to powdery mildew decreased progressively after the transition from bloom to cone development, although complete immunity to the disease failed to develop
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Categories: Pests
Environmental SustainabilityPublished July, 2018
Th ehop powdery mildew fungus Podosphaera macularis persists from season to season in the Pacific Northwestern United States through infection of crown buds because only one of the mating types needed to produce the ascigerous stage is presently found in this region. Bud infection and successful overwintering of the fungus leads to the emergence of heavily infected shoots in early spring (termed flag shoots).
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Categories: Pests
Environmental Sustainability
Published March, 2017
The downy mildew pathogen, Pseudoperonospora humuli, forms oospores abundantly in diseased hop tissue. Diverse monosporangial isolates of P. humuli derived from samples collected in Japan, Germany and the USA readily formed oospores within hop leaves when inoculated singly, suggesting homothallism. Single zoospore isolates also readily formed oospores within hop leaves, further supporting the homothallic nature of this oomycete. The majority of oospores were deemed viable based on cytoplasm characteristics and plasmolysis assays. However, disease symptoms failed to develop when hop leaves were inoculated with newly formed oospores, even when oospore conditioning was attempted with treatment with potassium permanganate or b-glucuronidase/arylsulphatase, brief exposure to freezing temperature, or passage through an earthworm
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Categories: Pests
Environmental Sustainability
Published August, 2020
Pseudoperonospora humuli is an obligate biotrophic oomycete that causes downy mildew (DM), one of the most destructive diseases of cultivated hop that can lead to 100% crop loss in susceptible cultivars. We used the published genome of P. humuli to predict the secretome and effectorome and analyze the transcriptome variation among diverse isolates and during infection of hop leaves. Mining the predicted coding genes of the sequenced isolate OR502AA of P. humuli revealed a secretome of 1,250 genes.
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Categories: Pests
Environmental SustainabilityPublished February, 2014
The hop looper, Hypena humuli Harris, is a reemergent pest of hop that often requires treatment to mitigate crop damage. In 4 yr of Þeld trials, plots treated with fungicides were observed to sustain less hop looper defoliation compared with nontreated plots. Further investigation revealed that abundance of hop looper and associated defoliation were reduced when the fungicide pyraclostrobin was appliedinlateJulytoearlyAugust.
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Categories: Pests
Environmental SustainabilityPublished February, 2014
The temporal development of biological control of arthropod pests in perennial cropping systems is largely unreported. In this study, the development of biological control of twospotted spider mite, Tetranychus urticae Koch, and hop aphid, Phorodon humuli (Schrank), in a new planting of hop in Oregon is described over a period of 9 yr (2005Ð2013). Both the abundance and diversity of natural enemies increased over time.
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Categories: Horticulture, Soil Health & Fertility
Environmental Sustainability
Published July, 2021
Hops and malt are the two main sources of nitrate in beer, with hops being the primary source in beers that are late-hopped or dry-hopped. A proof-of-concept study was performed to characterize how nitrogen fertilizer dose applied in the field during hop production influences nitrate accumulation in hop-forward beers. To quantify the dose-response relationship two contrasting nitrogen fertilizer rates, 90 and 269 kg/ha, were used to produce hops that differed in their nitrate concentrations (852 and 2651 mg/kg of nitrate, respectively).
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Categories: Horticulture, Soil Health & Fertility
Environmental SustainabilityPublished 2014
Podosphaera macularis, the causal agent of hop powdery mildew, is known to produce chasmothecia (formerly cleistothecia) in eastern North America and Europe. Ascocarps have not yet been reported from the Pacific Northwestern region of North America. Reasons for the apparent absence of chasmothecia in the Pacific Northwest were unknown. This study established that P. macularis is heterothallic and ascocarp ontogeny, maturation, dehiscence and ascospore infection proceed similarly to other powdery mildew fungi.
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Categories: Pests
Social SustainabilityPublished 2016
Demand for hoppy beers continues to grow and craft brewers are proving to be innovative in the ways they are introducing high volumes of hops into their brews. Hops are increasingly being added later in the brewing process in both dried whole-cone and pelletized form and many craft breweries are pioneering the addition of green, undried, high-moisture hops to the brewing process. Concurrently consumers are demanding wholistic inputs into the brews they consume, leading to concerns that hops may be contributing a pesticide load in beer
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Categories: Regulations
Economic SustainabilityPublished 2013
This guide was authored for the sole purpose of providing robust, minimum standards for hop processors regarding food safety, product quality, personnel, and proper data collection and retention. Practices outlined in this manual are borrowed from other similar industries as well as crafted specifically with smaller hop processors in mind
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Categories: Pests, Picking, Kilning, & Baling
Environmental Sustainability
Published April, 2025
As with all crops, coverage and penetration are the two main spraying issues. The challenge is to obtain even coverage throughout the bines and the cones, both horizontally and vertically. Spray will only penetrate into a canopy via liquid pressure or air-assistance.
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Categories: Health & Safety
Environmental SustainabilityPublished April, 2025
Organic hops production in the U.S. is finding a niche among the growing number of microbreweries that currently purchase organic hops from New Zealand and China. This publication looks at cultural requirements for organic hops, hops varieties, and recent research. It also provides a list of further hops resources.
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Categories: Organic Farming
Environmental Sustainability
Published April, 2025
Two of the most important arthropod pests of hop are the two-spotted spider mite and the hop aphid. There is a naturally occurring complex of predators and parasitic insects (parasitoids) that prey on these pests. Conserving and promoting these natural enemies can enable biological control to play a larger role in regulation of pest populations, reducing or even eliminating the need for chemical control measures in some situations. The potential for controlling these pests with biological control requires an understanding of the factors that promote and disrupt the ecological system within and around hop yards.
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Categories: Pests
Environmental SustainabilityPublished April, 2025
Commercial hop production is plagued by multiple pests, two of the most important being the two-spotted spider mite and hop aphid. The economic impact of chemically controlling these pests is significant and resistance issues provide further impetus to seek out other control options.
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Categories: Pests
Environmental Sustainability
Published April, 2025
When plants are infected with Hop stunt viroid, emergence and early growth is delayed in the spring. By mid-summer, the lengths of internodes of infected bines are reduced by onethird, resulting in the stunted appearance of infected plants that struggle to reach the top wire. As the bines mature, the development of laterals is inhibited and cones are borne on the sparse and shortened lateral branches.
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Categories: Pests
Environmental SustainabilityPublished April, 2021
Irrigation is essential for hop production in the Pacific Northwestern United States, the primary growing region in the U.S. Irrigation water supplies can be inadequate in drought years and may become more variable in the future due to climate variability and increasing non-agricultural demand. In this research, the impact of delayed timing of the first irrigation of the season on hop yield and cone quality metrics in the cultivars Cascade and Zeus over three years was evaluated
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Categories: Irrigation
Environmental Sustainability
Published May, 2019
The twospotted spider mite (Tetranychus urticae Koch) is a common pest in agricultural and ornamental crops. This pest can be controlled by resident predatory arthropods in certain situations. This research quantified the stability and resiliency of established conservation biological control of the twospotted spider mite in hop over a 5-yr period associated with nitrogen fertilization rate and use of a broad-spectrum insecticide.
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Categories: Pests
Environmental Sustainability
Published July, 2018
Hop looper, Hypena humuli Harris, can cause substantial defoliation and crop damage by feeding on hop leaves and cones. A 4-yr field study conducted in western Oregon evaluated the abundance of hop looper larvae and associated defoliation of leaves on plants fertilized with nitrogen rates ranging from 44.8 to 269 kg/ha. There was annual variation in abundance of hop looper and defoliation, with a tendency for increasing nitrogen rate to increase both abundance of hop looper and defoliation.
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Categories: Pests
Environmental Sustainability
Published June, 2015
Real-time PCR assays using locked nucleic acid (LNA) probes and high resolution melt (HRM) analysis were developed for molecular differentiation of Pseudoperonospora cubensis and P. humuli, causal agents of cucurbit and hop downy mildew, respectively. The assays were based on a previously identified single nucleotide polymorphism (SNP) in the cytochrome oxidase subunit II (cox2) gene that differentiates the two species.
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Categories: Pests
Environmental SustainabilityPublished July, 2016
Pollinators are critical to ecosystem health and agricultural productivity. Native pollinators provide important services to agroecosystems. However endemic bee diversity and abundance among different crops has not been extensively studied, especially among different perennial crops in Washington State.
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Environmental Sustainability
Published May, 2011
Hop (Humulus lupulus L.) is a dioecious, perennial vine grown in temperate regions across the world (Stevens et al., 1997). Today hop is being used for two purposes. The first and most prolific is its use in beer brewing. The other is a recent development, but ever growing interest in the use of hops for pharmaceuticals.
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Categories: Horticulture
Environmental Sustainability
Published January, 2017
Hop production, like all other water uses in the area, is facing water availability concerns. Deficit irrigation may address water scarcity issues in hop production. This study quantifies the effect of deficit irrigation on hop yield, quality, water productivity and grower profitability. Mt. Hood, Columbus, Chinook and Willamette cultivars were grown under three irrigation levels; 60, 80 and 100% of the crop’s irrigation requirement, using a sub-surface drip irrigation system
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Social Sustainability
Published October, 2019
Consumers in the United States are frequently exposed to residues of pesticides in their food. The existence of pesticide residues in food raises questions regarding what consumer health risks, if any, are posed by such chemical contaminants
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Categories: Regulations
Environmental Sustainability
Published April, 2018
The polyphagous pest Tetranychus urticae feeds on over 1100 plant species including highly valued economic crops such as hops (Humulus lupulus). In the key hop production region of the Pacific Northwest of the USA, T. urticae is one of the major arthropod pests. Over the years, T. urticae control has been dominated by the application of various acaricides. However, T. urticae quickly adapts to these acaricides by developing resistance.
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Categories: Pests
Social Sustainability
Published January, 2020
As a family-owned farm, Roy Farms works hard to understand regulations and guidelines related to COVID. They have had to adapt to the evolving situation in order to protect their employees’ health while continuing day-to-day farm operations.
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Categories: Health & Safety, Grower
Environmental SustainabilityPublished January, 2020
The results presented in this WSU publication serve as a general guide for evaluating the feasibility of producing conventional and organic hops in the Pacific Northwest as of 2020, with a capital and...
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Categories: Organic Farming
Environmental SustainabilityPublished October, 2020
Twospotted spider mite (Tetranychus urticae Koch) is a cosmopolitan pest of numerous plants, including hop (Humulus lupulus L.). The most costly damage from the pest on hop results from infestation of cones, which are the harvested product, which can render crops unsalable if cones become discolored.
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Categories: Pests
Environmental SustainabilityPublished June, 2019
A multi-year field study was conducted in Oregon and Washington to evaluate the influence of nitrogen fertilization rate and timing on cone quality and nitrate accumulation in cones. The impact of nitrogen rate on cone yield, levels of hop acids, total oil content, color, and nitrate level were year dependent.
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Social SustainabilityPublished December, 2020
As a result of continued disruptions and uncertainty to the U.S. food agriculture sector during the upcoming winter and spring agricultural seasons caused by the global novel Coronavirus Disease 2019…
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Categories: Health & Safety, Workers, Regulations
