Real Christmas trees contribute ~$2.5 billion to the US economy annually. True fir (Abies spp.) are the most popular trees and account for the majority of sales. The real Christmas tree commodity board identified aroma as the primary driver for consumers to purchase a real tree. We conducted consumer aroma panels for five (Fraser, noble, Nordmann, Trojan, and concolor) of the most popular fir Christmas trees in the US. Based on aroma characteristics alone, Fraser fir was found to be most liked while noble fir ranked last amongst consumers. Gas Chromatography Mass Spectroscopy metabolite profiling of terpene (the major drivers of conifer aroma) putatively identified 132 mono- and sesquiterpene and 48 diterpene metabolites across all five species. Among these, the sesquiterpene, β-bisabolene, was strongly correlated with consumer liking. These findings provide a resource to identify compounds positively associated with consumer preference to help guide Christmas tree genetic improvement efforts.

The Douglas-fir twig weevil (Cylindrocopturus furnissi Buchanan) (Coleoptera: Curculionidae) has recently emerged as a significant pest of Christmas trees grown in the Pacific Northwest United States. The larvae girdle and disfigure twigs, which adversely affects tree marketability. Trees produced for export are also routinely destroyed for phytosanitary reasons when C. furnissi is discovered at border crossings. Due to historically being a sporadic and benign pest on planted and natural Douglas-fir (Psuedotsuga menziesii), there is a lack of chemical management options. In laboratory experiments, we assessed the knockdown effects (ability to kill or incapacitate) of 4 insecticides commonly used on Christmas trees: one assay tested knockdown after direct contact for 24 h, and the other assay tested knockdown after being allowed to feed on treated twigs with 2 days, 7 days, and 14 days residuals. Concurrently, we monitored temperature and adult C. furnissi emergence at a noble fir bough farm for 2 years to estimate the ideal degree-day window for applying insecticides. Bifenthrin and esfenvalerate knocked down all weevils on contact within just 4 h, whereas chlorpyrifos and acephate failed to achieve 100% knockdown within 24 h. Only acephate failed to knock down more weevils than the control (water) after feeding on treated twigs, regardless of the insecticide residue age. Degree-day modeling revealed a variable emergence window between the 2 years but 50% of adult emergence occurred between approximately 1,000-1,100 degree days (1st January, 50 degrees F (10 degrees C), single sine). Future work should assess the resulting management recommendation: apply bifenthrin or esfenvalerate once annually just after 1,000 growing degree days for 2 or more years prior to harvest.

Botrytis cinerea causes gray mold disease of strawberry (Fragaria ×ananassa) and is a globally important pathogen that causes fruit rot both in the field and after harvest. Commercial strawberry production involves the use of plastic mulches made from non-degradable polyethylene (PE), with weedmat made from woven PE and soil-biodegradable plastic mulch (BDM) as emerging mulch technologies that may enhance sustainable production. Little is known regarding how these plastic mulches impact splash dispersal of B. cinerea conidia. The objective of this study was to investigate splash dispersal dynamics of B. cinerea when exposed to various plastic mulch surfaces. Mulch surface physical characteristics and conidial splash dispersal patterns were evaluated for the three mulches. Micrographs revealed different surface characteristics that have the potential to influence splash dispersal: PE had a flat, smooth surface, whereas weedmat had large ridges and BDM had an embossed surface. Both PE mulch and BDM were impermeable to water whereas weedmat was semi-permeable. Results generated using an enclosed rain simulator system showed that as the horizontal distance from the inoculum source increased, the number of splash dispersed B. cinerea conidia captured per plate decreased for all mulch treatments. More than 50% and approximately 80% of the total number of dispersed conidia were found on plates 10 and 16 cm away from the inoculum source across all treatments, respectively. A significant correlation between the total and germinated conidia on plates across all mulch treatments was detected (P<0.01). Irrespective of distance from the inoculum source, embossed BDM facilitated higher total and germinated splashed conidia (P<0.001) compared to PE mulch and weedmat (P = 0.43 and P = 0.23, respectively), indicating BDM's or embossed film's potential for enhancing B. cinerea inoculum availability in strawberry production under plasticulture. However, differences in conidial concentrations observed among treatments were low and may not be pathologically relevant.

The recent emergence of the fungus Cryptostroma corticale in Seattle, Washington, USA is concerning because of its invasive status in Europe, where it causes sooty bark disease of maples (SBD), killing both forest and urban trees. Additionally, the fruiting bodies (stromata) of C. corticale produce allergenic spores that can impact human health. Therefore, its presence in Washington has the potential to impact the state's populace and trees, including the native bigleaf maple, Acer macrophyllum. To better determine the distribution of C. corticale in western Washington, A. macrophyllum was surveyed on 50 Washington State Park properties. Bark samples were collected from trees with fruiting bodies resembling those of C. corticale and cores were removed from mature asymptomatic trees. The presence of C. corticale was confirmed using nested PCR. Acer macrophyllum with fruiting bodies of C. corticale were well distributed throughout western Washington, with an 89% detection rate at surveyed Park properties containing A. macrophyllum. Core samples indicated that latent infections appeared well distributed and common throughout western Washington on mature A. macrophyllum, with a 91% detection rate at surveyed Park properties containing A. macrophyllum and a 68% detection rate on cored trees. Signs of SBD and evidence of latent infections of C. corticale were widespread at surveyed properties. However, signs of SBD were rare on individual trees and the overall condition of A. macrophyllum was considered vigorous at the majority of Park properties. Awareness of C. corticale, SBD, and their likelihood to be present on a property containing A. macrophyllum in western Washington should help inform management actions and demonstrate the need for future research.

Phytophthora species are plant pathogens responsible for many notable biological invasions in agricultural, forests, and natural ecosystems. Detection and monitoring for invasive introductions of Phytophthora spp. is time and resource intensive. Development of citizen science detection and monitoring programs can aid in these efforts focused on reducing Phythophthora impacts. There are multiple methods for monitoring and detecting Phytophthora invasions suitable for citizen science approaches such as, leaf sampling, stream baiting or soil collections. Here we summarize five active projects in western North America where citizen scientists are aiding the monitoring and research efforts surrounding Phytophthora species and their impacts. Projects varied in scope, scale, methods, and capacity, but each project increased citizen scientists’ abilities for surveillance and advanced detection or knowledge of Phytophthora species. Some projects were integrated with school programs, others involved hands-on training with small groups, and another approach invited mass participation from interested citizens. Overall, all projects had positive outcomes multiplied across education, monitoring, and research. Together these case studies demonstrate how citizen scientists can amplify surveillance efforts, advance baseline knowledge, and reduce the impacts of biological invasions.

Gray bulb rot of tulips and bulbous iris is caused by the soil-borne fungal pathogen, Rhizoctonia tuliparum (Rtul). Sclerotia present in infected bulbs, as well as overwintering sclerotia in soil and field debris, are the primary sources of infection. A method for accurate and sensitive detection of Rtul from soil and infected bulbs, and estimation of inoculum threshold levels, is needed for the management of disease caused by this pathogen. We designed a unique set of primers targeting the ITS2 region of the Rtul genome and developed a highly sensitive quantitative PCR (qPCR)-based method for Rtul identification using these primers, where the threshold of detection was approximately 1 fg Rtul DNA. The assay was more sensitive with sclerotia collected from the field (natural) than with those grown in the lab, and more sensitive with natural-light than natural-dark sclerotia. Also, the detection method was more sensitive when sclerotia were extracted from soil than from bulb tissue. The qPCR method was highly specific, as no PCR amplification was detected when genomic DNA from 62 non-Rtul Rhizoctonia isolates from a wide range of anastomosis groups were tested. To understand the evolutionary relationships and genomic diversity of Rtul, we performed phylogenetics of the ITS1-5.8S-ITS2 region and ITS2-molecular morphometric characterization (MMC) of Rtul isolates. The three Rtul isolates whose ITS sequences were available in GenBank formed a distinct phylogenetic clade with Ceratobasidium anceps as the nearest relative. Furthermore, MMC analysis revealed genetic divergence among these three Rtul isolates.

Salal (Gaultheria shallon), Oregon grape (Berberis aquifolium), and red huckleberry (Vaccinium parvifolium) are common shrubs in the understory of northwestern forests and are ecologically, culturally, and economically important to the region. They are also sold in nurseries for use in ornamental landscapes and ecological restoration. These plant species were symptomatic for Phytophthora in nursery surveys in Washington State between 2011 and 2015. Symptoms observed on these three hosts resembled those of foliar Phytophthora infection on other woody broadleaf plants. The nursery plants were positive for P. ramorum, and Koch’s postulates were completed on potted plants of the three host species, illustrating their potential as a pathway of spread from nurseries to wildlands. We recommend these three hosts be added to the USDA-APHIS regulated host list, which will aid in the effort to prevent movement of P. ramorum into new areas.

Phytophthora species pose significant challenges to public gardens, but collaboration can help contaminated gardens minimize their impacts and remain open to the public. Phytophthora ramorum was detected at the Bloedel Reserve-a botanical garden in Washington State-in 2015 but has not been recovered from surveys of plant material since 2016 following coordinated regulatory responses, research activities, and adaptative management decisions. Here we summarize efforts that were made to reduce the impact of P. ramorum on the Bloedel Reserve and limit the spread of this pathogen to nearby landscapes. Regulatory responses included detection and removal of positive plants, soil steaming, and the development of best management practices in the Reserve. Measures to adapt management in the garden included supporting applied research, removal of host plants, fungicide sprays, trail maintenance, and signage. The garden also featured P. ramorum in their education and outreach programs and used this as an opportunity to teach the public about invasive species.

Climate shifts and concomitant weather extremes such as extended droughts make it difficult to determine the best seed sources for reforestation. Seed source selection based on current climate conditions avoids further disrupting biotic interactions that may confer ecosystem resilience, but seed source selection could also draw from populations adapted to anticipated future climate conditions. Knowledge of relationships between seed sources and adaptation to climatic variables helps evaluate options. This study used four common gardens of Pacific madrone (Arbutus menziesii Pursh) to model tree performance in height growth, dieback, mortality, and, at one site, phenology, using differences in abiotic variables from the tree’s geographic origins and the planting location. While the degree of variation explained by even the best models was relatively low, there were some trends. Patterns of growth and mortality differed across common garden sites, but the distance seeds were moved to the common garden site, seed source ecoregion, and the difference in the length of frost-free period between a seed source’s site of origin and the common garden site were in the best models for growth and mortality. Differences in mean summer precipitation, an indication of potential drought stress, were only in the best models for growth at the wettest and driest common garden sites. Trees more local to a common garden site generally had higher growth, and sometimes lower mortality. However, some Willamette Valley trees not local to a common garden site had relatively greater growth and low mortality so could be good candidates for broader seed movement. The abiotic factors that best explain growth and mortality were similar in less stressful and more stressful years, although models for stress years included more abiotic variables. Abiotic variables were better at explaining timing of spring leaf flush than the performance metrics, and spring flush did not correlate well to growth, dieback, or mortality. Our results support the importance of abiotic factors in predicting growth, mortality, and phenology in Pacific madrone, but their predictive capacity and relative importance depends on the site and may vary even for nearby sites.

Slugs are one of the most important pests of Christmas trees grown in the Pacific Northwest relative to load rejections in Japan, Hawaii and other Pacific Rim destinations (http://www.oregonlive.com/news/index.ssf/2008/11/hawaii_rejects_oregongrown_chr.ht ml). For example, when a shipment of trees contaminated with Arion slugs is discovered in Hawaii officials reject the load, and either ship it back to the Pacific Northwest or have it cleaned up in Hawaii at the shipper’s expense. Current strategies for managing slugs focus on a combination of chemical and cultural (e.g. shaking) measures. However, even with these approaches slugs continue to pose a significant economic problem for Christmas tree growers in the Pacific Northwest.

Pacific madrone (Arbutus menziesii) is an evergreen hardwood species in western North America that occurs from British Columbia to southern California. The species has high cultural and specialty wood values, and is also ecologically important for wildlife habitat, wildfire revegetation, and creating midstory canopy biodiversity in mixed conifer forests. Pacific madrone is experiencing unsustainable mortality (Lintz et al. 2016), but reasons for the decline are unknown. Foliar pathogens such as described by Zeller (1934) have been implicated because of their high visibility and association with defoliation. However, very little is known about the genetics of this species, including variation in resistance to pathogens and other adaptive traits.

In March 2015 Phytophthora ramorum was detected at The Bloedel Reserve, a 150 acre botanical garden in Kitsap County, WA. Infected plants were destroyed and the soil in an area surrounding these plants was steam-sterilized to a depth of 15 cm during the summer of 2015. An IPM program was developed in an effort to control the spread of P. ramorum and other Phytophthora species in the garden, reduce the risk of P. ramorum spread to the surrounding landscape, and minimize additional destruction of valuable plants and visual impacts to the garden. Several treatments were employed, including the use of Phytophthora-specific fungicides, removing host vegetation, soil steaming, replanting affected areas with non-host or host plant species that have shown some resistance to P. ramorum, and the use of Trichoderma biocontrol agents and mulch to reduce spread of disease from soil to plants. Surveys in the P. ramorum positive areas and perimeter were done during 2015-2018. Symptomatic foliage was collected and tested for Phytophthora using ELISA. Any ELISA positive samples were tested for P. ramorum with PCR. Isolates of P. ramorum were genotyped using microsatellite markers. Many of the P. ramorum positives were detected on certain native hosts. In February 2016, the IPM strategy was therefore modified to include the removal of native host vegetation within the positive areas. Fungicides were applied in the positive areas during 2016-2018. The rate of ELISA+ plants was between 37% - 90% during this time period. The rate of ELISA+ samples has decreased in the positive areas since the peak of 90% in October 2016 and has stayed below the initial 72% measured in January 2016. Seven NA1 microsatellite genotypes of P. ramorum were detected at Bloedel between March 2015 – February 2016. The two most commonly found genotypes were identical to the genotypes of P. ramorum from two nurseries in Washington State. The remaining five genotypes have only been detected at Bloedel and are very similar to the nursery genotypes. These are probably derived from the nursery genotypes rather than being new introductions. Fungicide applications and long term continual removal of native host plants in the positive areas, and the reapplication of Plant Helper (Trichoderma atroviride) in areas that were identified as higher risk due to slope and proximity of prior positive sites has been continued until the present. The Plant Helper is applied as a soil drench and then covered with a mulch that is made from chipped alder wood and other vegetation, but not containing host plant material, on the Reserve. Expanding the use of Trichodermas in the prior positive areas of the Reserve to include areas further from these known positive sites is being considered. Soil steaming was effective in the immediate areas of the positives that were detected, but there are extensive areas that should be protected from potential infestation, and there may be undetected infestations that could be mitigated by added populations of Trichoderma in the soil.

The most important step in any effective disease management strategy is proper diagnosis. Therefore, in an effort to assist growers with disease management, herbaceous peony (Paeonia lactiflora) samples were collected and submitted to our lab from 12 states in the United States to determine the range of diseases present in both landscape and commercial settings. Both morphological and molecular techniques were used in the identification of pathogens isolated from peony flowers, leaves, stems, and roots. Trials were conducted to confirm the ability of all pathogens to cause disease on healthy peony tissue. This survey revealed new species-host-state combinations in several states as well as five different fungal genera that had not previously been identified on peonies in the country: a Botryosphaeria sp., up to 3 Colletotrichum spp., Mycocentrospora acerina, a Phoma sp., and Pilidium concavum. Each of these pathogens have only been reported a few times worldwide and there is correspondingly little to no information available on their management. Given the need for growers to address these emerging disease issues, we outline potential management strategies for fungal peony pathogens. Our recommendations take into account general fungal disease management tools, published information on the specific biology of these organisms, observations of peony diseases over our years of fieldwork, and examples from other pathosystems that have been successful in managing diseases caused by the pathogens we have found on peonies.

Defining host-pathogen interactions between species of root-rotting Phytophthora and Abies in Christmas tree production areas is important for tailoring management activities on a regional scale and for developing molecular tools for identifying resistant host species. Classifying Abies species as resistant or susceptible is complicated by regional variation in abundance and aggressiveness of Phytophthora species and the influence of environment on symptom expression and host vigor. Because previous studies performed to assess host response to Phytophthora root rot (PRR) have focused on one or a few species of either the host or pathogen, a multifactorial experiment was conducted to assess the responses of seven species of Abies challenged with three isolates each of four Phytophthora species under contrasting temperature conditions. Evaluation of mortality, root rot severity, and remaining root biomass after 16 weeks of exposure to the pathogen confirmed prior inferences regarding inherent variation in the resistance responses of various species of Abies and demonstrated evidence of variation in aggressiveness among species of Phytophthora as well as different isolates of the same Phytophthora species. The ambient temperatures at which studies were conducted had a conspicuous effect on host mortality, root rot severity, and radial growth of Phytophthora. Understanding how host responses differ under variable pathogen attack and ambient environment will improve efforts to control PRR using host species substitutions on infested ground.

Peonies, Paeonia lactiflora and hybrids, are popular ornamental plants grown in landscapes and as cut flowers. As with many ornamental plants, the information on the etiology of peony diseases is incomplete with varying amounts of detailed descriptive material; sometimes validation of Koch's postulates is also lacking. In a survey to identify the range of diseases of peony in the United States, samples were obtained from 12 states. Fungal and oomycete plant pathogens recovered from symptomatic, diseased tissue were identified by morphology and BLAST identification of the internal transcribed spacer, glyceraldehyde 3-phosphate dehydrogenase, the 28s large subunit, and/or cytochrome c oxidase subunit 1 gene nucleotide sequences for representative isolates. Ten fungal or oomycete genera were identified, and Koch's postulates were confirmed for selected plant pathogens found during this survey. New disease reports are generated for several states, including five genera never previously reported on peonies in the United States: a Botryosphaeria sp., multiple Colletotrichum spp., Mycocentrospora acerina, a Phoma sp., and Pilidium concavum. The information gained from this survey will provide plant disease diagnosticians and growers a more comprehensive resource for understanding the regional prevalence of peony diseases and subsequently making better disease management decisions.

Genus Botrytis contains approximately 35 species, many of which are economically-important and globally-distributed plant pathogens which collectively infect over 1,400 plant species. Recent efforts to genetically characterize genus Botrytis have revealed new species on diverse host crops around the world. In this study, surveys and subsequent genetic analysis of the glyceraldehyde-3-phosate dehydrogenase ( G3PDH ), heat-shock protein 60 ( HSP60 ), DNA-dependent RNA polymerase subunit II ( RPB2 ), and necrosis and ethylene-inducing proteins 1 and 2 ( NEP1 and NEP2 ) genes indicated that Botrytis isolates collected from peony fields in the United States contained more species diversity than ever before reported on a single host, including up to 10 potentially novel species. Together, up to 16 different phylogenetic species were found in association with peonies in the Pacific Northwest, which is over a third of the total number of species that are currently named. Furthermore, species were found on peonies in Alaska that have been described on other host plants in different parts of the world, indicating a wider geographic and host distribution than previously thought. Lastly, some isolates found on peony share sequence similarity with unnamed species found living as endophytes in weedy hosts, suggesting that the isolates found on peony have flexible lifestyles as recently discovered in the genus. Selected pathogenicity, growth, and morphological characteristics of the putatively new Botrytis species were also assessed to provide a basis for future formal description of the isolates as new species.

The objective of this study was to identify the parasite causing the formation of root hair galls on eelgrass (Zostera marina) in Puget Sound, WA. Microscopic and molecular analyses revealed that a novel protist formed plasmodia that developed into sporangia in root hair tip galls and released biflagellate swimming zoospores. Root hair galls were also observed in the basal section of root hairs, and contained plasmodia or formed thick-walled structures filled with cells (resting spores). Phylogenetic analyses of 18S rDNA sequence data obtained from cells in sporangia indicated that the closest relative of the parasite with a known taxonomic identification was Plasmodiophora diplantherae (86.9% sequence similarity), a phagomyxid parasite that infects the seagrass Halodule spp. To determine the local geographic distribution of the parasite, root and soil samples were taken from four eelgrass populations in Puget Sound and analyzed for root hair galls and parasite DNA using a newly designed qPCR protocol. The percent of root hairs with galls and amount of parasite DNA in roots and sediment varied among the four eelgrass populations. Future studies are needed to establish the taxonomy of the parasite, its effects on Z. marina, and the factors that determine its distribution and abundance.