Hop Yards Research Articles

Viruses and Viroids Infecting Hop: Significance, Epidemiology, and Management.

The hop (Humulus lupulus) is a hardy, climbing, dioecious, perennial plant native to Europe, Asia, and North America (172). The genus Humulus belongs to the family Cannabaceae and contains three species: H. japonicus, H. lupulus, and H. yunnanensis (32,117). Hops are grown predominantly for their cones (strobiles), which contain glands producing resins, essential oils, and polyphenols (Fig. 1). These compounds are used primarily to add bitterness and aroma to beer. The most important of these compounds for brewing are the alpha acids. Alpha acids are acylsubstituted phloroglucinols, differing from each other only in the nature of the acyl R side chain. They can be separated into humulone (R = isovaleryl), cohumulone (R = isobutryl), adhumulone (R = alphamethyl butryl), prehumulone, and posthumulone (127). The main properties of alpha acids in relation to beer production are improved foam stability, suppression of gushing, and contributions to bacteriological stability (48). The bitterness of beer is related to stereoisomer formation of each major alpha acid in the brewing process (124). Beta acids are predominantly separated into lupulone, colupulone, and adlupulone. They have limited bittering power but are particularly important because of their bactericidal properties (194). More than 200 other essential oils also occur within the cones, including hydrocarbons and oxygenated and sulfur-containing compounds, which are responsible for the aroma and flavor of the final product (170). Hops are also grown for their medicinal and soporific effects, as ornamental plants, and as edible delicacies (146). The areas in which hop can be grown are limited by strict day length and temperature requirements for flowering and hence cone production. Production is generally restricted around 35° latitudes in both hemispheres (32,117). Supplementary artificial lighting has been used to produce hops in areas of lower latitudes, such as in South Africa (196). In 2005, the most significant regions of hop production (i.e., countries with >1,000 ha) were Germany, the Czech Republic, Poland, Slovenia, Ukraine, the United Kingdom, the northwestern states of the United States (Idaho, Washington, and Oregon), and China. Lesser quantities were grown in 14 other European countries. A few other countries grow 500 ha or less, most notably Japan, Argentina, Australia, South Africa, New Zealand, and India (26). The largest area of production was in Germany (17,161 ha producing 34,466.8 metric tons), while 11,956 ha were grown in the United States, producing 24,002 metric tons (26). Viruses and viroids pose significant constraints to the production of high yields of hop cultivars worldwide. In some countries, such as Australia and New Zealand, these pathogens are considered the only significant pathological problems. This is due to the absence of severe fungal diseases, such as powdery mildew (154) and downy mildew (155). Infections by five viruses and two viroids are or have been widespread and important in commercial hop yards. A further 12 viruses (of which two are poorly characterized) and 1 viroid have been reported in hop; these either have limited distributions or occur only sporadically and are not considered important. The viruses considered generally important are the three carlaviruses, Hop mosaic virus (HpMV) (3,20,94,156), Hop latent virus (HpLV) (4,21,55,150,180), and American hop latent virus (AHLV) (5,22,149); the ilarvirus Apple mosaic virus (ApMV) (27,28,46,64); and the nepovirus Arabis mosaic virus (ArMV) (6,9,50,82). The important viroids infecting hops are Hop latent viroid (HpLVd) (10,14,24,25,151) and Hop stunt viroid (HpSVd) (162–164,201). Although the problems posed by viruses and viroids for the production of hops are not unique among perennial crops, they are particularly challenging because the rates of spread are often much higher than in other crops such as top fruit. As such, the control measures used with hops present a good case study for the control of these pathogens in crops where long life (hop yards are typically kept for up to 20 years and may last 50 years) means they are repeatedly exposed to infection. The reasons for rapid spread relative to tree fruit crops are unclear, but one might speculate that the very rapid and massive annual growth (the entire aboveground part of the plants is replaced every year, and main stems generally grow more than 5 meters in only 3 to 4 months) in closely spaced plantings favors both mechanical transmission (for HpSVd, HpLVd, and ApMV) and heavy infestations with aphids (for the carlaviruses). The study of hop viruses and viroids also emphasizes the need to fully understand and quantify the effects of these pathogens on yield and/or quality of crops, which are highly dependent on cultivar, pathogen strain, and environmental conditions.

A Decade of Hop Powdery Mildew in the Pacific Northwest

Hop powdery mildew, caused by the fungus Podosphaera macularis, was confirmed for the first time in hop yards in the United States Pacific Northwest in 1997. The US hop industry experienced significantly crop loss and damage from the disease, but new knowledge, grower experience, and management approaches have allowed the industry to survive the introduction of this damaging pathogen. This review provides an overview of research on and progress towards economically sustainable management of hop powdery mildew in the US, and future directions for research and further innovation. Accepted for publication 2 January 2008. Published 14 March 2008.

Chemical ecology and conservation biological control

Elucidating the chemical ecology of natural enemies, herbivores and host plants is important in the development of effective and successful integrated pest management (IPM) strategies where abundance and distribution of natural enemies could be manipulated by semiochemicals for improved conservation biological control (CBC). In response to attack by herbivores, plants produce semiochemicals called Herbivore-Induced Plant Volatiles (HIPVs) which act to repel pests and attract their natural enemies. Damaged, and in some cases, intact plants may also produce volatile signals that warn other plants of impending attack. Some of these intact plants are used as intercrops in ‘push–pull’ strategies; cropping systems based on stimulo-deterrent principle, where the target crop is intercropped with herbivore repellent plants (push) while attractant plants (pull) are planted around this intercrop. The intercrop, in addition to repelling the herbivores, attracts and conserves natural enemies thereby ensuring continued suppression of the pests. This natural delivery of semiochemicals for CBC is currently being exploited by smallholder farmers in eastern Africa in the management of cereal stemborers in maize and sorghum. Synthetic HIPVs also have the potential to effectively recruit natural enemies, thereby improving CBC as has been demonstrated in a series of field experiments in vineyards and hop yards in the Pacific Northwest of the United States. Potentially, plants could be ‘turned on’ by synthetic HIPV signals, and therefore become sources of natural enemy-recruiting volatiles. With the rapid development of plant molecular biology, modification of secondary plant metabolism is also possible which could allow appropriate semiochemicals to be generated by plants at certain growth stages. By identifying the promoter sequences associated with external plant signals that induce biochemical pathways, plant defense genes could be ‘switched on’ prior to insect attack. We review recent research on ‘push–pull’ strategies and synthetic HIPVs in recruitment of beneficial arthropods and warding off pest attack.

Sequential Sampling for Estimation and Classification of the Incidence of Hop Powdery Mildew II: Cone Sampling.

Sequential sampling models for estimation and classification of the incidence of powdery mildew (caused by Podosphaera macularis) on hop (Humulus lupulus) cones were developed using parameter estimates of the binary power law derived from the analysis of 221 transect data sets (model construction data set) collected from 41 hop yards sampled in Oregon and Washington from 2000 to 2005. Stop lines, models that determine when sufficient information has been collected to estimate mean disease incidence and stop sampling, for sequential estimation were validated by bootstrap simulation using a subset of 21 model construction data sets and simulated sampling of an additional 13 model construction data sets. Achieved coefficient of variation (C) approached the prespecified C as the estimated disease incidence, , increased, although achieving a C of 0.1 was not possible for data sets in which < 0.03 with the number of sampling units evaluated in this study. The 95% confidence interval of the median difference between of each yard (achieved by sequential sampling) and the true p of the original data set included 0 for all 21 data sets evaluated at levels of C of 0.1 and 0.2. For sequential classification, operating characteristic (OC) and average sample number (ASN) curves of the sequential sampling plans obtained by bootstrap analysis and simulated sampling were similar to the OC and ASN values determined by Monte Carlo simulation. Correct decisions of whether disease incidence was above or below prespecified thresholds (pt) were made for 84.6 or 100% of the data sets during simulated sampling when stop lines were determined assuming a binomial or beta-binomial distribution of disease incidence, respectively. However, the higher proportion of correct decisions obtained by assuming a beta-binomial distribution of disease incidence required, on average, sampling 3.9 more plants per sampling round to classify disease incidence compared with the binomial distribution. Use of these sequential sampling plans may aid growers in deciding the order in which to harvest hop yards to minimize the risk of a condition called "cone early maturity" caused by late-season infection of cones by P. macularis. Also, sequential sampling could aid in research efforts, such as efficacy trials, where many hop cones are assessed to determine disease incidence.

Sequential Sampling for Estimation and Classification of the Incidence of Hop Powdery Mildew I: Leaf Sampling.

Hop powdery mildew (caused by Podosphaera macularis) is an important disease of hops (Humulus lupulus) in the Pacific Northwest. Sequential sampling models for estimation and classification of the incidence of powdery mildew on leaves of hop were developed based on the beta-binomial distribution, using parameter estimates of the binary power law determined in previous studies. Stop lines, models that indicate that enough information has been collected to estimate disease incidence and cease sampling, for sequential estimation were validated by bootstrap simulations of a select group of 18 data sets (out of a total of 198 data sets) from the model-construction data, and through simulated sampling of 104 data sets collected independently (i.e., validation data sets). The achieved coefficient of variation (C) approached prespecified C values as the achieved disease incidence ( ) increased. Achieving a C of 0.1 was not possible for data sets in which < 0.10. The 95% confidence interval of the median difference between the true p and included zero for 16 of 18 data sets evaluated at C = 0.2 and all data sets when C = 0.1. For sequential classification, Monte-Carlo simulations were used to determine the probability of classifying mean disease incidence as less than a threshold incidence, pt (operating characteristic [OC]), and average sample number (ASN) curves for 16 combinations of candidate stop lines and error levels (α and β). Four pairs of stop lines were selected for further evaluation based on the results of the Monte-Carlo simulations. Bootstrap simulations of the 18 selected data sets indicated that the OC and ASN curves of the sequential sampling plans for each of the four sets of stop lines were similar to OC and ASN values determined by Monte Carlo simulation. Correct classification of disease incidence as being above or below preselected thresholds was 2.0 to 7.7% higher when stop lines were determined by the beta-binomial approximation than when stop lines were calculated using the binomial distribution. Correct decision rates differed depending on the location where sampling was initiated in the hop yard; however, in all instances were greater than 86% when stop lines were determined using the beta-binomial approximation. The sequential sampling plans evaluated in this study should allow for rapid and accurate estimation and classification of the incidence of hop leaves with powdery mildew, and aid in sampling for pest management decision making.

Spatial Heterogeneity of the Incidence of Powdery Mildew on Hop Cones.

The spatial heterogeneity of the incidence of hop cones with powdery mildew (Podosphaera macularis) was characterized from transect surveys of 41 commercial hop yards in Oregon and Washington from 2000 to 2005. The proportion of sampled cones with powdery mildew ( p) was recorded for each of 221 transects, where N = 60 sampling units of n = 25 cones assessed in each transect according to a cluster sampling strategy. Disease incidence ranged from 0 to 0.92 among all yards and dates. The binomial and beta-binomial frequency distributions were fit to the N sampling units in a transect using maximum likelihood. The estimation procedure converged for 74% of the data sets where p > 0, and a loglikelihood ratio test indicated that the beta-binomial distribution provided a better fit to the data than the binomial distribution for 46% of the data sets, indicating an aggregated pattern of disease. Similarly, the C(α) test indicated that 54% could be described by the beta-binomial distribution. The heterogeneity parameter of the beta-binomial distribution, θ, a measure of variation among sampling units, ranged from 0.01 to 0.20, with a mean of 0.037 and a median of 0.015. Estimates of the index of dispersion ranged from 0.79 to 7.78, with a mean of 1.81 and a median of 1.37, and were significantly greater than 1 for 54% of the data sets. The binary power law provided an excellent fit to the data, with slope and intercept parameters significantly greater than 1, which indicated that heterogeneity varied systematically with the incidence of infected cones. A covariance analysis indicated that the geographic location (region) of the yards and the type of hop cultivar had little effect on heterogeneity; however, the year of sampling significantly influenced the intercept and slope parameters of the binary power law. Significant spatial autocorrelation was detected in only 11% of the data sets, with estimates of first-order autocorrelation, r1, ranging from -0.30 to 0.70, with a mean of 0.06 and a median of 0.04; however, correlation was detected in only 20 and 16% of the data sets by median and ordinary runs analysis, respectively. Together, these analyses suggest that the incidence of powdery mildew on cones was slightly aggregated among plants, but patterns of aggregation larger than the sampling unit were rare (20% or less of data sets). Knowledge of the heterogeneity of diseased cones was used to construct fixed sampling curves to precisely estimate the incidence of powdery mildew on cones at varying disease intensities. Use of the sampling curves developed in this research should help to improve sampling methods for disease assessment and management decisions.

Further Field Evaluation Of Synthetic Herbivore-Induced Plan Volatiles As Attractants For Beneficial Insects

Fifteen synthetic herbivore-induced plant volatiles (HIPVs) were field-tested for attractivity to beneficial insects in two experiments conducted in an open field and a hop yard in Washington State. Eleven insect species or families showed significant attraction to 13 HIPVs. The ladybeetle, Stethorus punctum picipes, was attracted to sticky traps baited with methyl salicylate (MeSA), cis-3-hexen-1-ol (He), and benzaldehyde (Be). The minute pirate bug, Orius tristicolor, was attracted to traps baited with MeSA, He, Be, and octyl aldehyde (Oa), and the bigeyed bug, Geocoris pallens, responded to MeSA, indole, and trans-2-hexen-1-al. The mymarid wasp, Anagrus daanei, was attracted to He, Oa, and farnesene. The chloropid fly, Thaumatomyia glabra, was highly attracted to methyl anthranilate. Insect families responding to HIPVs included Syrphidae (MeSA, He), Braconidae ((Z)-3-hexenyl acetate, He, cis-jasmone (J), methyl jasmonate (MeJA), methyl anthranilate (MeA)), Empididae (MeSA), Sarcophagidae (MeSA, Be, J, nonanal and geraniol), Tachinidae (Be), and Agromyzidae (MeSA). Micro-Hymenoptera (primarily parasitic wasp families) were attracted to MeSA, He, and indole. These results are discussed with respect to known properties and bioactivity of the tested HIPVs and to their potential as tools for recruiting natural enemies into agroecosystems.

Spatial Pattern Analysis of Hop Powdery Mildew in the Pacific Northwest: Implications for Sampling

ABSTRACT The spatial pattern of hop powdery mildew was characterized using 3 years of disease incidence data collected in commercial hop yards in the Pacific Northwest. Yards were selected randomly from yards with a history of powdery mildew, and two to five rows were selected for sampling within each yard. The proportion of symptomatic leaves out of 10 was determined from each of N sampling units in a row. The binomial and the beta-binomial frequency distributions were fit to the N sampling units observed in each row and to SigmaN sampling units observed in each yard. Distributional analyses indicated that disease incidence was better characterized by the beta-binomial than the binomial distribution in 25 and 47% of the data sets at the row and yard scales, respectively, according to a log-likelihood ratio test. Median values of the beta-binomial parameter theta, a measure of small-scale aggregation, were near 0 at both sampling scales, indicating that disease incidence was close to being randomly distributed. The variability in disease incidence among rows sampled in the same yard generally increased with mean incidence at the yard scale. Spatial autocorrelation analysis, used to measure large-scale patterns of aggregation, indicated that disease incidence was not correlated between sampling units over several lag distances. Results of a covariance analysis showed that heterogeneity of disease incidence was not dependent upon cultivar, region, or time of year when sampling was conducted. A hierarchical analysis showed that disease incidence at the sampling unit scale (proportion of sampling units with one or more diseased leaves) increased as a saturation-type curve with respect to incidence at the leaf level and could be described by a binomial function modified to account for the effects of heterogeneity through an effective sample size. Use of these models permits sampling at the sampling unit scale while allowing inferences to be made at the leaf scale. Taken together, hop powdery mildew was nearly randomly distributed with no discernable foci, suggesting epidemics are initiated from a well-distributed or readily dispersible overwintering population. Implications for sampling are discussed.

Field-Testing of Methyl Salicylate for Recruitment and Retention of Beneficial Insects in Grapes and Hops

Evidence for recruitment and retention of beneficial insects in grapes and hops using controlled-release dispensers of methyl salicylate (MeSA), a component of herbivore-induced volatile blends, is presented. In a replicated experiment conducted in a juice grape vineyard, sticky cards in blocks baited with MeSA captured significantly greater numbers of five species of predatory insects (Chrysopa nigricornis, Hemerobius sp., Deraeocoris brevis, Stethorus punctum picipes, Orius tristicolor) than unbaited blocks. Four insect families (Syrphidae, Braconidae, Empididae, Sarcophagidae) were also significantly more abundant in the MeSA-baited blocks, as indicated by sticky card captures. Canopy shake samples and sticky card monitoring conducted in a MeSA-baited, unsprayed hop yard indicated development and maintenance of a beneficial arthropod population that was nearly four times greater than that present in an unbaited reference yard. Four times as many S. punctum picipes and six times as many O. tristicolor were sampled in the MeSA yard. Similar contrasts in abundance of these predators and others were apparent when compared with levels recorded in the yard in previous years. The large population of predatory insects in the MeSA-baited hop yard was associated with a dramatic reduction in spider mite numbers, the major arthropod pest of hops, in late June, and subeconomic populations were maintained for the rest of the season. The evidence presented here is highly suggestive that the use of controlled-release MeSA in a crop could increase recruitment and residency of populations of certain beneficial insects. This strategy may have the potential to enhance the efficacy and reliability of conservation biological control in crop pest management.

Sensitivity of Pseudoperonospora humuli (the Causal Agent of Hop Downy Mildew) from Oregon, Idaho, and Washington to Fosetyl-Al (Aliette)

Failures of fosetyl-Al (Aliette) to control hop (Humulus lupulus) downy mildew, caused by Pseudoperonospora humuli, have recently occurred in northern Idaho and Oregon. To determine if resistance of the pathogen to the fungicide has developed, leaf disk assays were conducted to compare sensitivity of P. humuli isolates from the different U.S. hop-growing regions to isolates from a research yard where exposure to fosetyl-Al had not occurred for at least 10 years. Dose response curves of transformed data were linear. The fosetyl-Al concentration effective against 50% of the P. humuli isolates (ED50) from each location was estimated from the linearized data. The ED50 values indicate that fosetyl-Al was about one-third as effective against P. humuli isolates from commercial hop yards in northern Idaho and Oregon and about one-half as effective against isolates from southern Idaho compared to isolates from the research yard. Commercial yards in Washington were similar to the research yard. Accepted for publication 3 August 2004. Published 11 August 2004.

Synthetic Herbivore-Induced Plant Volatiles as Field Attractants for Beneficial Insects

Abstract Evidence for field attraction by beneficial insects to synthetic herbivore-induced plant volatiles (HIPVs) is presented. Three synthetic HIPVs (methyl salicylate, (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene) were evaluated in a Washington state hop yard during April–October 2002 for attractiveness to beneficial insects. The predatory mirid, Deraeocoris brevis (Uhler), and the anthocorid, Orius tristicolor (White), were attracted to sticky cards baited with (E)-3-hexenyl acetate, while the geocorid, Geocoris pallens Stal., and hover flies (Syrphidae) were attracted to methyl salicylate-baited cards. The coccinellid, Stethorus punctum picipes (Casey), was attracted to both HIPVs in July and September. The (E)-4,8-dimethyl-1,3,7-nonatriene did not attract any beneficial insects. Lygus hesperus Knight, Leptothrips mali (Fitch), Anagrus spp., other Miridae, Coccinellidae, and parasitic Hymenoptera were not attracted to the three HIPVs tested. The possible exploitation of HIPVs in enhancin...

Field evaluation of herbivore-induced plant volatiles as attractants for beneficial insects: methyl salicylate and the green lacewing, Chrysopa nigricornis.

Synthetic methyl salicylate (MeSA), a herbivore-induced plant volatile (HIPV), was demonstrated to be an attractant for the green lacewing, Chrysopa nigricornis, in two field experiments conducted in a Washington hop yard. Significantly greater numbers of C. nigricornis were trapped on MeSA-baited sticky cards (mean: 2.8 +/- 0.4/card/week) than on unbaited cards (0.45 +/- 0.15) during June-September. Cards baited with two other HIPVs, hexenyl acetate and dimethyl nonatriene, did not attract more C. nigricornis than did unbaited traps (0.30 +/- 0.10, 0.44 +/- 0.15, respectively). MeSA-baited Unitraps captured 1.9 +/- 0.5 C. nigricornis/trap/week during July-August compared to 0.20 +/- 0.20/trap/week in methyl eugenol-baited traps and 0.03 +/- 0.03/trap/week in unbaited traps. The potential use of MeSA in enhancing C. nigricornis populations in Washington hop yards as an aid to conservation biological control of aphids and mites is discussed.

Toxicity of imidacloprid to Galendromus occidentalis, Neoseiulus fallacis and Amblyseius andersoni (Acari: Phytoseiidae) from hops in Washington State, USA

The toxicity of systemic and spray formulations of imidacloprid to Galendromus occidentalis Nesbitt, Neoseiulus fallacis Garman and Amblyseius andersoni (Chant) from hop yards in Washington State was evaluated in laboratory bioassays. The field rate of imidacloprid for hop aphids (0.13 g a.i. l) was highly toxic (100% mortality) to G. occidentalis and N. fallacis but less so (35.6% mortality) to A. andersoni. Half and quarter rates were also highly toxic to G. occidentalis and N. fallacis (79.5-100% mortality) but again had lower toxicity to A. andersoni (8.2-31.3% mortality). Systemic toxicity (via consumption of spider mite motiles feeding on leaf discs cut from imidacloprid-treated (0.13 g a.i. l) dwarf bean plants) was also high for G. occidentalis (98.3% mortality), as was toxicity from dried residues (93-98% mortality). Residual toxicity to N. fallacis was also high (89% mortality). The significance of these results for biological control of spider mites in hops and other crops is discussed.

Selectivity of the acaricide, Bifenazate, and aphicide, pymetrozine, to spider mite predators in Washington hops

Toxicity of an acaricide, bifenazate, and an aphicide, pymetrozine, to the phytoseiid mites, Galendromus occidentalis Nesbitt, Neoseiulus fallacis Garman and Amblyseius andersoni (Chant), and the coccinellid spider mite predators, Stethorus punctum picipes Casey and Harmonia axyridis Pallas, was examined in laboratory bioassays. The impact of applications of these pesticides on phytoseiids and a guild of spider mite/aphid predators in commercial hop yards in Washington was also evaluated. In bioassays, bifenazate at the full field rate was moderately toxic to the phytoseiids and coccinellids (37-81% mortality) but less toxic at half and quarter rates (0-44% and 0-11%, respectively). Pymetrozine was non-toxic to all predators at all rates. Phytoseiid (G. occidentalis/N. fallacis) populations and a guild of non-phytoseiid spider mite/aphid predators in hop yards appeared unaffected by single applications of half or three-quarter rates of bifenazate and the full rate of pymetrozine. Bifenazate and pymetrozine show great potential as selective pesticides that can be used in a sustainable hop arthropod management program based on recruitment and conservation of endemic natural enemies.

Support systems and training methods for dwarf hops (Humulus lupulus L.)

SummaryAn experiment was conducted over three years to determine the effects of string and netting support systems and various training methods on the growth, development, yield and quality of dwarf hops (cultivar First Gold). The crop was grown in a hop yard with wirework of 2.29 m height, in rows set 2.44 m apart. The hops were planted 45 cm apart in the rows. In one support treatment, coir strings were tied between the top and bottom wire at 22.5 cm intervals and in the other 14 cm square polypropylene netting was threaded onto the top and bottom wire. Superimposed on these treatments were training treatments. These were full training (three rounds of hand work), delayed training (chemical defoliation in spring followed by two rounds of training), gapping (plants left to self train and one round of final training in July) and no training. Regular measurements were made of crop growth and development and at harvest, yield and alpha-acid content were measured. The highest yields were attained on the netting support system and with the full training method. However, gapping or no training would often provide a better economic return because the reduction in cost can be greater than the value of lost yield. Delayed training consistently reduced yield for little or no cost saving and is therefore not appropriate for dwarf hop systems. Better yields were associated with plants reaching the top wire earlier and producing longer laterals. Whilst not measured, it would appear that the number of laterals produced by each plant is an important determinant of yield, as the number of cones per lateral was similar in all treatments. The implications of the results for growers of dwarf hops are discussed.

Mite abundance and phenology on commercial and escaped hops in Washington State, USA

The abundance and phenology of two-spotted spider mite (Tetranychus urticae) and its phytoseiid and nonphytoseiid predators, were monitored monthly on commercial (pesticide-treated) and escaped (pesticide-free) hops in the Yakima Valley, Washington over two seasons. Mean abundance of T. urticae for both seasons was generally low (2.8-27.7 mites/leaf) and did not differ significantly between commercial and escaped hop sites, despite application of up to four miticides at commercial sites. Miticide control of T. urticae failed at three hop yards in 1999 producing substantial populations (300/leaf) in August. Six phytoseiid species (Galendromus occidentalis, Neoseiulus fallacis, Typhlodromus pyri, Amblyseius andersoni, Typhlodromus caudiglans, Proprioseiopsis lindquisti), were identified with G. occidentalis and N. fallacis accounting for > 95% of phytoseiids sampled. Mean abundance of phytoseiids for both seasons did not differ significantly between commercial and escaped hops. Six nonphytoseiid predators of T. urticae were recorded with the mite-eating ladybird, Stethorus picipes, most abundant. The incidence of nonphytoseiid predators was more than three times greater in escaped than in commercial hops. The possible importance and utilization of an assemblage of natural enemies containing phytoseiid and nonphytoseiid predators for biological control of T. urticae populations in Washington hops, is discussed.

A DNA-BASED VARIETAL IDENTIFICATION PROCEDURE FOR HOP LEAF TISSUE

A DNA-based method was evaluated for varietal identification of immature hop plants. Total DNA was isolated from hop leaf tissue and used as a template for the Polymerase Chain Reaction (PCR) to produce DNA fragments of various sizes. Specific patterns of DNA fragments were produced from DNAs of different hop varieties when short, random-sequence primers were used to direct the PCR. The unique patterns of DNA fragments produced with certain primers formed the basis for the varietal identification method described. This procedure would be most valuable for testing planting stock before establishing a new hop yard.

Microbial biomass, metabolic activity and nutritional status determined from fatty acid patterns and poly-hydroxybutyrate in agriculturally-managed soils

Soil microbial biomass, fatty acid pattern, poly-β-hydroxybutyrate content and selected physiological variables were studied in agriculturally-managed soils with different cropping histories: crop rotation, hops and grassland. Significant correlation was observed between substrate-induced respiration, the amounts of adenine nucleotides and the total amounts of phospholipid fatty acids. The highest microbial biomass was found in a grassland soil, the lowest in soils which were formerly cultivated with hops. Additionally, the highest ratio of poly-β-hydroxybutyrate: total phospholipid fatty acids, the largest specific respiration rate and the lowest amounts of the adenylate energy charge were obtained in one of the former hop yards. Due to the frequent treatment of hop plants with fungicides a large amount of copper had accumulated in this former hop yard. The condition of the soil had resulted in the creation of a microbial community with markedly different biochemical characteristics compared to communities associated with grassland soil or crop rotation soil. The principal component analysis was able to discriminate the different soils when applied to hydroxy fatty acids. The profile of fatty acids in the copper-contaminated soil indicated an increase in numbers of Gram-negative bacteria. A lower concentration of branched chain fatty acids revealed a decreased proportion of Gram-positive bacteria in both former hop yard soils.

Tinged with Gold: Hop Culture in the United States.

Today hop growing remains a viable commercial enterprise only in parts of far western United States--notably in Washington. But, as James Fenimore Cooper remembered, mid-nineteenth century in Cooperstown, New York, was a time when the 'hop was king, ' and whole countryside was one great hop yard, and beautiful. In Tinged with Gold, Michael A. TomIan explores all aspects of hop culture in United States and provides a background for understanding buildings devoted to drying, baling, and storing hops. The work considers history of these structures as it illustrates their development over almost two centuries, result of agrarian commercialism and nearly continuous technological improvement. In examining context in which buildings were constructed, Tomlan considers growth, cultivation, and harvesting of plant; economic, social, and recreational activities of people involved in hop culture; and record of mechanical inventions and technical developments that shaped hop kilns, hop houses, and hop driers and coolers in various areas where crop flourished. The work challenges assumptions about noncommercial nature of American agriculture in eighteenth and early nineteenth centuries and raises important questions about folk tradition of hop houses, arguing that designs of these buildings were rational responses to commercial imperatives rather than continuance of arcane English or European customs. Tinged with Gold brings hop culture to life as it explores history of this neglected aspect of rural agriculture. Because work demonstrates that significance of a relatively obscure building type can befully appreciated if placed in its historical context, it provides a model for studying other rural structures. Drawing upon an impressive array of primary and secondary sources, this work is a definitive history of hop culture in United States.

Virulence of an Aphid-Derived Isolate of Beauveria bassiana (Fungi: Hyphomycetes) to the Hop Aphid, Phorodon humuli (Homoptera: Aphididae)

The potential for biological control of the hop aphid using an aphid-derived isolate of Beauveria bassiana was investigated in the laboratory and field. In initial bioassays using conidial suspensions at dosages ranging from 104 to 108 a conidia/ml, the isolate exhibited a high level of virulence to Phorodon humuli (Schrank), yielding a LC50 of 1.37 × 105 conidia/ml. LT50 values decreased with increasing conidial dose, being 11.1 ± 4.2, 8.4 ± 4.0, 5.0 ± 1.5, 3.6 ± 1.5, and 3.1 ± 1.1 d at 104, 105, 106, 107, and 108 conidia/ml, respectively. A potential for long-term control was demonstrated when conidial suspensions were applied to aphid-infested potted hop plants. Aphids increased only slightly during a 4-wk period on potted hop plants treated with a suspension of 107 conidia/ml. This was significantly lower than the net increase found on the controls and on plants treated with a suspension of 105 conidia/ml. However, there was no mycosis detected in aphids when a 107 conidia/ml suspension was applied in an aphid-infested commercial hop yard.