On the first day of winter, Daniel Volk, Forest Health Project Coordinator for Cleveland (OH) Metroparks reported that a coordinated survey has confirmed the presence of beech leaf disease link to DMF in four new states — Massachusetts, New Jersey, Rhode Island, and West Virginia. In all, the disease is now known to be established in 71 counties in the US and Canada. Funding was provided by the USFS Forest Health Management “emerging pest” program.
2021 survey efforts will focus on high risk counties adjacent to affected counties.
Cleveland Metroparks has several resources available on its website and will continue to post updated information there as it becomes available.
I posted a blog urging recipients to participate in these searches last June link I hope you will do so again in 2021.
range of American beech
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
In August I blogged that import volumes had crashed … US imports from Asia declined each month from January through June (Mongelluzzo Dec 14; full citations at end of blog). However, the economic rebound over the summer brought a surge in imports that continues. Given our concern about introductions of tree-killing pests, it is not good news that imports from Asia are driving the growth in imports.
US imports from Asia during the first 11 months of 2020 were 2% higher than the figure from the first 11 months of 2019. In November alone, the U.S imported 1.6 million TEUs [twenty-foot equivalent units; a standard measurement that counts incoming volume as though contained in twenty-foot-long containers] worth of goods from Asia. Imports in December are projected to remain high (Mongelluzzo Dec 14; full citation at end of blog).
Imports from Asia were 1.626 million TEU in December – up 29.9% from December 2019 (although still lower than October and August). December imports were pushed by record e-commerce sales and shipments of personal protective equipment (PPE) and medical supplies. For all of 2020, imports from Asia totaled 16.6 million TEU, up 4.1% from 2019 (Mongelluzzo Jan. 19)
This surge in imports – which began in late June — is certain to continue at least for the next two months as retailers ship more merchandise before some factories in Asia close for the Lunar New Year (Mongelluzzo Jan 19).
Because of the history of tree-killing pests introduced from Asia, I have blogged most often about the situation at West Coast ports. However, in 2020 there has been a noticeable shift to East and Gulf Coast ports because of the congestion and delays at West Coast ports. Thus, in November 2020, West Coast ports handled 60.2% of imports from Asia; East Coast ports handled 33.7%; Gulf Coast ports handled 5.7%. The East Coast figure is 30% higher than over the same period in 2019. At New York-New Jersey specifically, the increase was 35.1% (Mongelluzo Dec 16). Imports to Gulf Coast ports continue to rise; Gulf Coast ports handled only 4.8% of total US imports from Asia during the first nine months in 2019 and less than 3% before the widening of the Panama Canal (in 2016) (Angell October 28). Link to blog #203 midNov (In future, goods shipped from Asia across the Arctic Ocean to the U.S. east coast could add to the pest risk confronting our already hard-hit Eastern Deciduous Forest.)
Pacific Coast Ports
According to Mongelluzzo (December 9), the Los Angeles-Long Beach port complex (LA-LB) set records for US imports from Asia in August and again in October. The port complex handled 2.5 million TEU of imports from Asia in the three-month period of August through October. Despite shippers’ concern about delays, LA-LB is expected to continue to handle the bulk of Asian goods entering the country in coming months.
The ports of Los Angeles-Long Beach handle 50% of US imports from Asia. From July 2020 through February 2021, these ports received an average of 791,838 TEU each month – a 23% increase over the 2019 average of 642,000 TEU per month (Mongeluzzo April 2021).
Ports in the Southeast
As reported by Ashe (December 10), several ports in the southeast US are seeing record import volumes caused by retailers’ restocking, e-commerce, and Christmas shopping. November import volumes hit all-time highs in Savannah and Port of Virginia, while they were up year over year in Charleston. The three port authorities say the surge is the result of demand for furniture, bedding, refrigerators, freezers, and air conditioners – reflecting Americans’ current focus on improving their homes. Imports also include artificial Christmas trees (which have been a vector of pests in the past – as has furniture).
offloading cargo at Savannah; photo by F.T. Campbell
The volume of imports into Savannah from all sources surged 34% over the November 2019 volume. Imports from Asia rose 36%. Imports of furniture rose 42% in August and September. “Hardware, home goods, machinery, and appliances from Asia were up double digits,” according to Georgia Port Authority CEO Griff Lynch. Import volumes from Asia rose 36% in Virginia and 32% in Charleston.
Vessels Carry More Containers
Another threat of increased pest introductions arises from the increasing size of container ships. Increasing proportions of vessels with the capacity to carry more than 10,000 containers are arriving. Since 2010, the proportion of such ships arriving at West Coast ports has risen from 1.1% to 75.5%. The proportion arriving at East Coast ports has grown since the opening of the widened Panama Canal in 2017. The proportion of high-capacity ships visiting East Coast ports has risen from 3% in 2017 to 15% during the first 10 months of 2020. Gulf Coast ports receive few such vessels because the serve a smaller share of the U.S. market. The largest ships serve the trade from Asia primarily (Mongelluzzo Dec. 21, 2020). Of course, arrival of ten to fifteen thousand containers at once surely strains Custom’s inspection staff.
container ship in Savannah; Photo by F.T. Campbell
Imports from Geographic Regions Other Than Asia
Imports (from all sources) through New York and New Jersey ports were 22% percent higher in October 2020 than in October 2019 (Angell November 10). As noted above, most of the higher volume of imports originated in Asia.
According to Journal of Commerce staff (November 30), containerized imports from the Caribbean and Central America grew a negligible 0.1% over the same period last year. Principal ports for this trade are in Florida and along the Gulf Coast, but include Wilmington, DE, and Philadelphia.
According to JOC staff (November 2), containerized cargo import volumes from all regions flowing through the busiest US Gulf Coast ports declined 2.3% in the first seven months of 2020 compared to the same period in 2019.
Non-containerized cargoes — i.e., dry bulk, liquid bulk, roll-on/roll-off (ro-ro), and oversized/heavy-lift freight — are not included in these data. Dry bulk cargo through Houston has been reported to suffer problems in infested dunnage (wood used to brace non-containerized cargo, such as steel beams). Link to blog 173 February 2020
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
dwarfed Ulmus davidiana; photo by Krzsztof Zianek; Wikipedia Commons
USDA APHIS is seeking public input on a risk assessment that is intended to evaluate the risk of allowing importation of dwarf elm trees (bunjae) from South Korea. Importation of these trees is currently prohibited under APHIS’ authority to require a risk assessment before importation under the NAPPRA program. Upon receiving the Korean request, APHIS must decide whether to maintain the prohibition, or alter it. The risk assessment can be obtained here. Comments are due January 11, 2021.
I urge those with expert knowledge about phytophagous insects, nematodes, and fungal and other pathogens to prepare your own comments to APHIS.
[A year ago, Korea sought permission to export dwarfed maple trees to the U.S. CISP commented on APHIS’ risk assessment at that time; see my blog here. I believe APHIS has not yet decided whether to allow such imports. Many of the same issues apply here.]
After reviewing the risk assessment, I conclude that there are too many high-risk pests to support removing the taxon from the current restrictions. The history of introductions on dwarfed trees in the past supports this conclusion. The most conspicuous is the citrus longhorned beetle (Anoplophora chinensis) – the reason for the original NAPPRA listing – but there have been others, too.
The risk assessment has some strengths. I applaud the assessors for noting in each pest review that since the proposed imports are propagative material, all the pests will arrive on living hosts. The assessment then discusses – briefly! – the mechanisms by which the pest or pathogen could disperse to infest new trees – e.g., flight, rain splash, irrigation water. However, I think the assessment is sometimes too cautious in describing probable invasive risks.
I also find several important weaknesses in both the risk assessment process generally and specific findings.
Weaknesses of the Risk Assessment Process
The assessors do not discuss the potential efficacy of pest-management actions taken by the exporter or by USDA at ports of entry. They outlined production and harvesting practices that they assumed would apply to the exported plants. They warned that the risk assessment finding could not be applied to plants produced or handled other under conditions.
I am troubled by the assessors’ decision not to consider the plants’ ages and sizes. There is evidence that age and size are very important in determining the likelihood of pest presence. Perhaps the decision reflects the assumption that the exported plants would be less than four years old. Still, the assessors should have been transparent about the reasoning behind this decision.
The assessment underestimates “uncertainty”. One manifestation is the decision to provide little information about whether pests or pathogens known to attack several Eurasian species of Ulmus might also attack North American elm species. This gap arises, I believe, from the International Plant Protection Organization (IPPC) and APHIS requirement that risk analysts consider only pest-host relationships described in the literature or inferred from port interception data. I find this narrow approach to be a weakness, given how many unknown pest-host relationships have proved to be highly damaging. This issue arises specifically in the reviews of the nematode Meloinema kerongense and several powdery mildews (Erysiphe kenjiana, E. ulmi and Podosphaera spiralis) – all of which are identified as affecting at least some elm species.
Perhaps the missing information has fewer consequences here, since the NAPPRA process does not require that APHIS prove the pest-host relationship for every pest evaluated in order to justify retaining the prohibition on importation. The well-documented history of detecting the citrus longhorned beetle in artificially dwarfed trees and as a pest of the Ulmus genus provides more than sufficient justification to retain trade restrictions. Still, if APHIS is conducting a formal risk assessment, it should be thorough. Anything else sets an unfortunate precedent.
Finally, in cases when some of the hosts considered are commercial crops – e.g., fruit trees – the assessment often does not include forest trees as economically important resources at risk.
Questions re: some of specific pests in the analysis
3.2.1. Cerambycidae (Coleoptera)
The risk assessment notes the minimal information available regarding several cerambycid beetles present in Korea that are capable of feeding on elm trees. Collectively, these beetles have a wide host range — Acer, Alnus, Citrus, Ficus, Hibiscus, Juglans, Malus, Morus, Quercus, Populus, Prunus, Pyrus, Salix, Sorbus, and Ulmus. The beetles can thrive in the climate present across most of the Lower 48 states (USDA Plant Hardiness Zones 6-9). The risk assessment does mention the risk to urban and forest trees. It also mentions British detection of A. chinensis larvae in twigs of imported maple trees, but for some reason does not mention past U.S. detections and introductions of this beetle in maple bonsai/bunjae trees in Tukwila, Washington. Is this because the detections were 20 years ago? Does the passage of time make the detections any less relevant?
trees removed for CLB eradication in Tukwila, Washington
The analysis of this tortricid moth notes its broad host range, including Abies, Acer, Betula, Fraxinus, Populus, Quercus, Salix, Sorbus, Tilia, and Ulmus. Yet the analysis makes no mention of the potential impact of moth larval feeding on the buds and flowers of forest trees. Nor does it discuss the moth’s impact in Canada, where it is established. The Canadian experience seems quite pertinent and is an obvious omission.
3.2.3. Meloinema kerongens
This nematode is present on elms in Korea. The assessors could find no information on the damage it causes to its hosts there. Again, there is no discussion of possible vulnerability of American elms. Apparently the nematodes are considered likely to survive the importation process, when the trees will be bare root. The assessors say that since the dwarfed trees (once imported) are likely to be planted in pots, that might limit the nematodes’ dispersal into native soil habitats and ability to infect new trees. This finding is troubling because it is likely that nematodes or their eggs could be present in the pots’ soil, and if that soil leaks from the pot or is disposed of during repotting or with other actions, pests could become established in native soil.
3.2.5. Helicobasidium mompa
This fungus causes root rot on multiple genera in 44 plant families. The list of hosts includes Pinus spp., Populus spp., Prunus spp., and Quercus spp. It appears to thrive in a wide climatic range covering virtually the entire Lower 48 states (USDA Plant Hardiness Zones 2-11). The fungus is spread via rain or irrigation water. I note that experience with the Phytophthora genus of brown algae has demonstrated how difficult it can be to control pathogens that spread in rain or irrigation water – in both nurseries and the wild.
Other Potential Pests
I urge experts to review the long list of pests not analyzed—especially the nematodes that inhabit the root and rhizosphere. Analysts did not analyze them because they are ectoparasites; they decided that ectoparasites were unlikely to remain with the dwarfed trees when they are shipped bare-root.
I also wonder whether the mistletoe Viscum album – a parasitic plant – might be spread onto the dwarfed trees by birds perching on branches or shelter structures above the production facilities. Assessors thought that dormant mistletoe on the plants would not be easily detected during visual inspection at the ports.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Arctostaphylos uva-ursi (bear berry); photo by Sten Porse, Commons.Wikipedia
The California Department of Food and Agriculture (CDFA) is seeking input on proposed pest ratings for two species of Phytophthora: Phytophthora occultans and Phytophthora quercetorum. Each has the potential for being a serious pest in California and being spread throughout the United States. Therefore it is important to weigh in on this process. The first deadlines for comments is December 18.
These risk rating proposals can be found at https://blogs.cdfa.ca.gov/Section3162/ The website also has instructions for sending comments. This process can be clumsy so, if it doesn’t work, send your comments directly to the webmaster.
In general, the State assigns each potential pest a rating of A, B, or C. Those rated “A” are most likely to cause harm and also most subject to State regulation. Under “B”, the County Agricultural Commissioners have discretion to take regulatory actions. Pests ranked at “C “are not subject to any State enforced regulatory actions. The “C” rating is supposed to be assigned to pests that are widely distributed in the state and are expected to have a “medium” to “low” impact on vegetation (cultivated or wild) in the state.
Phytophthora occultans
Proposed for risk rank “C “. Comments are due December 18th.
Phytophthora occultans is a recently described species found in nurseries in Europe and in some U.S. states (including Oregon). It was recently detected in the San Francisco area of California.
The State proposes to rate Phytophthora occultans as a level “C” pest. This is insufficient. A rank of “B” is more appropriate, for the following reasons.
1) The data presented in the CDFA proposal are too limited to judge the species’ distribution in California. The proposal refers to only “two detections, two years apart, in San Francisco County.” By ranking it “C”, CDFA seems to assume the pathogen is widespread, based on detections in Europe and other states, without U.S. evidence
The available record does not indicate that CDFA made any attempt to determine the extent of the P.occultans infestations — no survey of other plants at the contractor’s nursery or at other nurseries and no consultation with a larger group of stakeholders.
2) CDFA limits discussion of possible impacts to hosts listed in the literature –which belong to multiple plant families. It makes no mention that additional hosts are likely to be discovered (as has often happened with regard to the host ranges of other pathogens in the Phytophthora genus). If the host range expands, as I expect it will, the impact to restoration activities, rare plants, wildlands and nurseries is more likely to be significant, not medium to low.
Furthermore, several of the known host species are congeners of species that are federally listed as endangered or threatened, i.e., species in the genera Ceanothus and Arctostaphylos. I think it is highly unwise to disregard in risk assessments the probability that listed species will prove to be hosts.
In conclusion, please submit comments to California Department of Food and Agriculture urging it to assign a risk rating of “B” to Phytophthora occultans.
Instructions are contained in the proposal. If this process doesn’t work (sometimes it is clumsy), send your comments directly to the webmaster.
Over the past 5 years, P. quercetorum has been detected in association with oak trees, primarily coast live oak (Quercus agrifolia), in four counties in California, two in the Central Valley (Fresno, Sacramento), two on either side of the San Francisco Bay (Alameda, San Francisco). There have been no interceptions of the species by CDFA border inspectors. The species had earlier been associated with oak roots and rhizosphere soil of oak forests in the eastern and north central US. Its pathogenicity is said to be unknown – and difficult to separate from impacts of other, often co-occuring Phytophthoras. CDFA assigns a rank of “high” with regard to economic impact, although it says there are no reports quantifying economic losses in plant production facilities.
CDFA believes that the species is likely to be able to establish wherever its hosts can grow (a rank of “high”). Hosts include red maple (Acer rubrum), English ivy (Hedera helix), several eastern oaks, and a second California oak, interior live oak (Q. wislizeni). CDFA assigns this a rank of “moderate” host range.
The environmental impact is ranked as “high” since the pest could lower biodiversity, disrupt natural communities, or change ecosystem processes; and the pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.
The overall ranking for the “Consequences of Introduction” is “high”.
However, the recommended ranking is “C”, which – again – means the pest is not subject to any State enforced regulatory actions. “C” rated pests are widely distributed in the state and are expected to have a “medium” to “low” impact on vegetation (cultivated or wild) in the state.
Why would CDFA recommend “no action” for yet another Phytophthora species that is known to attack two of the state’s most ecologically important oaks and possibly many more species? Even when the exact impacts are unclear … Especially when the principal means of spread is planting trees in restoration areas – a deliberate human action.
According to the USDA Forest Service, coast live oak (Quercus agrifolia) is a conspicuous tree in lower-elevation oak woodlands of California, which collectively occupy about 10 million. It is co-dominant in the southern oak woodlands. CLO trees generally occur on mesic sites such as north slopes, alluvial terraces, canyon bottoms, or upper streambanks. Coast live oak woodlands are some of the most important habitats to wildlife in California; they provide habitat for black bear, black-tailed deer, rodents and lagomorphs, and various upland game and nongame birds – including those that feed on acorns and cavity nesters. The birds including the federally endangered least Bell’s vireo and least tern.
Coast live oak is more fire resistant than other California oak species.
Coast live oak is favored for use in rehabilitation projects throughout its range. It is used in watershed improvement, restoration, and wildlife habitat rehabilitation projects.
CLO is already under pressure by predation by deer and cattle; sudden oak death (SOD; causal agent Phytophthora ramorum); goldspotted oak borer (GSOB – Agrilus auroguttatus); and sometimes the polyphagous shot hole borer (PSHB; Euwallaceawhitfordiodendrus) and its associated Fusarium fungus. [These three non-native organisms are described here.]
range of Q. wislizeni; USDA Forest Service map
According to the USDA Forest Service, interior live oak (Quercus wislizeni) occurs over about 16% of California’s landscape, especially in the Inner Coast Ranges, the foothills of the southern Cascade Range, and the Sierra Nevada. Among California’s red oaks, interior live oak has the highest tolerance for xeric conditions. It usually dominates the “scrub” or “live oak” chaparral vegetation types in the Inner Coast Ranges and the Sierra Nevada.
CNPS Calscape lists several insects associated with the species.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
As we know, the SOD pathogen Phytophthora ramorum infects more than 100 plant species [APHIS host list posted here]. Some are killed, some not. Some support production of spores (=sporulation), and thus promote spread of the disease – either in nurseries and plantings, or in the wild. Conditions under which P. ramorum infects specific plant species also varies.
In both the ornamental plant industry and natural environments, transmission is driven mostly by foliar hosts.
Matteo Garbelotto and colleagues have carried out studies aimed at improving our understanding of the differences in host-pathogen interactions, and their meaning vis a vis persistence and spread of the disease – especially in wildland situations. The experiments were carried out five or more years ago, funded by the Farm bill Section 7721 funding. See the full reference at the end of this blog.
The team ranked 25 ornamental plant species representing ten families for susceptibility to P. ramorum and infectivity (spore production). They also tested potential differences among three of the genetic lineages of the pathogen—NA1 (prevalent in U.S. forests), NA2 (found in some nurseries in Pacific coast states), and EU1 (found in nurseries and – since 2015 – in some wildland forests in Oregon). The team also studied the effect of temperature on infectibility. Their goal was to help focus regulations so they will be more effective.
The studies clearly show that the relationship between P. ramorum and various hosts is complex – both susceptibility and infectibility vary depending on the host species, pathogen genetic lineage, and environmental conditions, especially temperature. Results of testing of leaves for the presence of the pathogen were affected by such experimental choices as the concentration of zoospores, temperature, plant host, pathogen genotype, and by the interaction between host and pathogen genotype. Stem results were mostly affected by host and host-pathogen genotype interaction.
Hosts bearing the most severe infections do not always support the highest levels of sporulation, so they are not necessarily the most likely to spread the disease.
Regulators also cannot always generalize re: the pathogen’s impact on plant hosts based on the hosts’ taxonomic relationship. Results were fairly similar for congeneric species within the genera Rosa, Prunus, and Syringa, but quite different for species within the genera Ilex, Gaultheria, and Osmanthus.
It is clear that basing regulatory or best management practices on any one pathogen-host-environment relationship is likely to lead to failure, leaving our forests inadequately protected
The findings that pertain most directly to early detection of infections and those that otherwise promote spread of the pathogen are my focus here.
Hosts that Support Sporulation / Spread of Disease
At least five host species are much more infectious than Rhododendron catawbiense. Hosts that support the highest levels of sporulation were Syringa vulgaris, Hamamelis intermedia, and Syringa meyeri. Hosts that support medium-high levels of sporulation were Rosa gymnocarpa and Syringa pubescens subsp. patula.
Two of the Syringa species support high levels of sporulation, but rank low on overall susceptibility. Rosa gymnocarpa ranked fourth for levels of sporulation, but only fifteenth for overall susceptibility. At least six other species join this group of taxa that are highly infectious without displaying noticeable symptoms. Note than none of these top disease drivers is included in the so-called “filthy five” genera which are the focus of federal and state detection efforts. These genera are Rhododendron spp., Camellia spp., Viburnum spp., Pieris spp., and Kalmia spp.
One of the “filthy five” is Rhododendron catawbiense. It is often used as a standard against which to compare other species’ vulnerability. R. catawbiense supports a somewhat lower level of sporulation than do the species listed in the preceding paragraph. Again, disease severity is not a reliable cue to the likelihood of supporting sporulation and disease spread. Thus, the Hamamelis intermedia was the only species that scored high for both sporulation and susceptibility.
Temperatures Affect Infection Rates
A temperature of 20°C [68o F] was found to be ideal for maximum sporulation by all three genotypes. However, the NA1 genotype was a relatively good sporulator at 12oC [53oF]. The NA2 genotype sporulates prolifically at 25°C [77oF], but produces fewer sporangia than the other two genotypes at 12oC. These findings suggest which genotype might pose a greater risk in warmer or cooler regions than those supporting the current wildland infestations in California and Oregon. Thus, if NA2 spreads via the nursery trade to warmer regions, such as the area of the Southeast identified by various risk maps developed in the past [See maps on pages 14 – 16 in chapter 5 of Fading forests III, available here], it might pose a higher risk. This discovery intensifies concern arising from the fact that many of the P. ramorum-infected plants shipped to Indiana – and presumably other eastern states – in 2019 were of the NA2 lineage. States that received infected plants in 2019 included Alabama, Arkansas, Kentucky, Missouri, North Carolina, Tennessee, Virginia, and West Virginia.
Considering individual host species, Gaultheria shallon, R. catawbiense, Osmathus delayayi and Hamamelis intermedia supported good sporulation at the higher temperatures whereas Laurus nobilis, Syringa vulgaris, and Magnolia stellata supported better sporulation in cooler climates. Note that H. intermedia and S. vulgaris support prolific sporulation; the latter is a “symptomless superspreader”.
Garbelotto et al. note that Magnolia stellata is both highly susceptible and highly infectious at 12°C and thus able to spread the infection in colder areas. This advice to limit use of this species in cooler areas runs counter to horticultural experts’ guidance to plant this shrub in USDA Hardiness Zones 4–9 – which include virtually all the lower 48 except the most northern parts of Montana, North Dakota, and Minnesota. Clearly, star magnolia is a popular plant in colder regions. At the other end of the spectrum, Gaultheria shallon, Hamamelis intermedia, and Mahonia aquifolia were both highly susceptible and infectious at 25 °C, thus their use should be limited in warmer areas. All three include warm regions in their native ranges.
Early Detection
There are two ways to carry out early detection surveys.
(1) The first is detection of infection in plants themselves. Garbelotto et al. determined that 14 plant species are highly or moderately susceptible to infection even with relatively limited inoculum sources. Intense monitoring of these species would be likely to detect new infestations. Three of the highly susceptiblespecies, namely Syringa meyeri, Syringa pubescens subsp. patula and Hamamelis intermedia, are potentially more susceptible than R. catawbiense.
Hamamelis x intermedia ‘Angelly’ 01.JPG Wikimedia Commons
Based on the relative ease of pathogen re-isolation from the following host species after they had been inoculated at low levels, Syringa meyeri, Syringa pubescens subsp. patula, Hamamelis intermedia, Syringa vulgaris, Osmanthus delavayi, and Magnolia grandiflora indicated that a larger number of plants in the production facility had become infected.
(2) A second approach to early detection monitoring would be to focus on those host taxa able to support the most robust sporulation when infected by low levels of inoculum. This approach emphasizes curtailing spread.
As I noted above, Garbelotto et al. conclude that five species could spur significantly faster disease spread due to higher transmission rates coupled with higher susceptibility rates. These five species are Syringa vulgaris, S. meyeri, and S. pubescens subsp. patula; Hamamelis intermedia; and Rosa gymnocarpa. Note than none of these disease drivers is included in the so-called “filthy five” genera on which regulators focus now detection efforts.
Several species appeared less diseased, but supported more vigorous sporulation (e.g., Syringa vulgaris,S. pubescens subsp. patula and Rosa gymnocarpa). Others were more diseased but supported less sporulation (e.g., Prunus laurocerasus and Prunus lusitanica). Therefore, nursery managers and regulators should not rely on visual assessment of disease intensity to judge spread risk.
Other Information
Comparing the three genotypes, EU1 was most aggressive in terms of disease incidence at both low and high inoculum loads. At low levels of inoculum, NA1 lineage was comparable in terms of disease severity.
However, at higher inoculum loads NA1 was clearly the most infectious based on the number of sporangia produced on infected hosts. Garbelotto et al. conclude that the co-mingling of the EU1 and NA1 lineages in Oregon forests might result in a highly destructive forest disease, as both virulence and transmission potential would be maximized. There is the further risk that the presence of the two genetic lineages, which have different mating types, might enable sexual reproduction/ genetic exchange between the two lineages.
Sources
Matteo Garbelotto, M., D. Schmidt, T. Popenuck. 2020. Pathogenicity and infectivity of Phytophthora ramorum vary depending on host species, infected plant part, inoculum potential, pathogen genotype, and temperature. Plant Pathology 2020;00.1
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
dead tanoak killed by P. ramorum in Oregon; photo courtesy of Oregon Department of Forestry
Stunning 2019 Nursery Outbreak – Continuing Story
I have blogged often about the sudden oak death pathogen Phytophthora ramorum. The most recent blogs have focused on last year’s episode in which infected plants were sent to retail nurseries in many states. Indeed, the 2019 outbreak led to the largest trace-forward investigation for the USDA APHIS’ Phytophthora ramorum program in a single year for more than a decade. A year later, much is still unclear. For example, based on reports last year, I told you that 18 states had received positive plants. APHIS now says it was 14.
In response to states’ requests, APHIS issued a “Hotwash Report” (described in the June 2020 newsletter of the California Oak Mortality Task Force (COMTF); see source list at the end of the blog for the url). The “Hotwash Report” says APHIS traced the infected plants back to two nurseries, but I have obtained information about efforts at only one – in Washington state – and even that information is not as explicit as I think should be. In the April COMTF newsletter, the Washington State Department of Agriculture reports only that compliance surveys at one wholesale shipping nursery would be more intense than usual. I believe the second nursery implicated in the event is in British Columbia, but the Canadian Food Inspection Agency has said it saw no evidence that a Canadian nursery had shipped infected plants to the U.S.
Indiana officials reported (Press et al.) that the infected plants received in that state were of the NA2 clonal lineage. This is the first report of the NA2 lineage outside British Columbia, Washington, and California and is thus especially significant. The outbreak caused Indiana authorities to ordered destruction of more than 6,100 rhododendron plants at retail outlets in Indiana. (April COMTF newsletter)
According to the June 2020 COMTF newsletter, APHIS revised its Phytophthora ramorum Domestic Regulatory Program Manual (available here). APHIS also reviewed the protocol governing responses to detection of P. ramorum in retail nurseries (available here). The agency also plans to carry out a full program review but no timeline has been announced.
It is not clear to me whether these actions satisfy the states or – most importantly – address the reasons why such a large breakout of nursery infestations escaped current regulatory safeguards.
APHIS Slow Walks a Revised Host List
Meanwhile, carrying out a promise made in May 2019 when APHIS revised the SOD regulations, APHIS has posted a revised list of officially recognized P. ramorum hosts (available here). Finally! The new list replaces one from 2013.
The new list recognizes only one new species (Gaultheria procumbens, eastern teaberry) as a proven host, based on completion of Koch’s postulates. (The scientific paper was published five years ago!) So far, APHIS would only recognize a host after Koch’s postulates were completed. But the agency has been unwilling to pay for the experimental work required.
That situation might be changing: APHIS says it is reviewing scientific publications and ongoing research. The agency also invites scientists to contact the national program manager regarding plant taxa that they believe should be added to the regulated plant taxa list.
Meanwhile, we know that scientists have completed Koch’s postulates on several new hosts: Brisbane box, Lophostemon confertus, taken from samples of street trees dying in central Sausalito, Marin Co., California (COMTF June newsletter); and seven species of Arctostaphylos (manzanita) (COMTF April newsletter). So far, there’s no word from APHIS as to if or when it might act on these.
Nursery Situation in Individual States
California
Inspections under various federal and state regulatory requirements have detected infected plants in five nurseries (COMTF June newsletter). Two are in counties with widespread infestations that ship only within the state. Infected plants were Camellia and Loropetalum (COMTF April newsletter). Three other nurseries, also that ship within the state, tested positive only in previous years. Trace investigations completed at four of these nurseries by June had detected no additional positive plants. (COMTF June newsletter)
Oregon
Western Oregon has a climate that favors P. ramorum. One result is intensification and spread of the forest infestation (see below); another is a perpetual problem with infected nurseries.
In fall 2019, Oregon Department of Agriculture detected positive plants and soil at an interstate shipper. The plants were destroyed. Trace-back detected no further positive detections. The areas with infested soil were taped off until authorities can carry out steaming to decontaminate (COMTF April newsletter).
Meanwhile, trace-back from a previously identified retail location led to a second commercial interstate shipper. Camellia, Pieris, and Rhododendron plants tested positive, along with three soil samples and one groundwater sample. This was the first detection for this wholesale location (COMTF April newsletter).
Then, a routine inspection detected P. ramorum at a third interstate shipper in early March 2020. As of April, seven Rhododendron plants tested positive. This was also the first detection at this particular nursery (COMTF April newsletter).
Meanwhile, the spring compliance surveys at 10 Oregon nurseries that ship interstate found no P. ramorum (COMTF October newsletter).
In August, Oregon Department of Agriculture conducted soil steaming at three nurseries that previously tested positive. The action was successful at two but not at the third due to irrigation issues. APHIS and ODA are working with the nursery to create an enhanced mitigation plan focusing on irrigation at the nursery (COMTF October newsletter).
However, trouble continues. In July, a North Carolina nursery reported positive Rhododendron plants that had been purchased from an Oregon nursery. Traceback detected infected Rhododendron plants at the site. Further tracebacks have been triggered at the locations where this material was purchased – apparently yet another nursery. The nursery is undergoing the final assessment to sign a federal compliance agreement and will be added to the list of nurseries sampled by ODA in fall (COMTF October newsletter).
Washington
Washington officials continue to detect P. ramorum in water bodies that have proved difficult to trace back to a plant source. Positive water samples were collected again from the pond at the botanic garden in Kitsap County – as has been true for most years since 2015. Despite the continuing presence of the pathogen in the pond, authorities have not been able to find infected plants in recent years, including in 2020.
Authorities also detected a water-positive at a nursery participating in the P. ramorum compliance program. They have scheduled additional vegetation and water sampling (COMTF April newsletter). It is not stated whether this is the nursery apparently responsible for the 2019 spread event.
A third positive water sample was collected on a creek in Snohomish County. The state Department of Agriculture plans to follow up with two nurseries in the drainage. One had previously tested positive (COMTF April newsletter).
In June, the state conducted a trace-forward investigation on plants from a positive out-of-state nursery. Most plants had been sold at the retail level and were untraceable. However, 37 Rhododendron planted in several residential locations were sampled; six plants at four sites were positive. The Confirmed Residential Protocol has been enacted at all four locations (COMTF August 2020). Authorities also treated the soil at two of the planting sites (COMTF October newsletter).
The Risk of New Phytophthora Introductions Is Dire
The COMTF June newsletter summarizes the findings of studies by European forest pathologists. As I reported in an earlier blog, European researcher have identified more than100 previously unknown Phytophthora species through intensive surveys conducted during 2013 – 2019 in natural ecosystems of Japan, Taiwan, Vietnam, Indonesia, Chile, Nicaragua, Panama, Curacao, Egypt and eight European countries. Overall, 13,242 isolates were obtained, which could be assigned to 65 known and 101 previously unknown species. Two of the most damaging – P. cinnamomi and P. ramorum – are most likely native to Southeast Asia. The scientists recommend extensive host-range testing of forest tree and horticultural crop species to assess the potential threat posed by the import of living plants from Southeast Asia. Several presentations and factsheets with further information may be found here. https://www.ponteproject.eu/
Early in the year, I attempted to persuade APHIS to begin studies of possible hosts’ vulnerability, but I was told that APHIS does not do research. I also approached the Agriculture Research Service and USDA Forest Service. Perhaps academic scientist could obtain funding to carry out such studies through grants funded by the Plant Pest and Disease Management and Disaster Prevention Programs (under Section 7721 of the Plant Protection Act) or National Institute of Food and Agriculture.
Wildland Infestations – Threat to native plants; interactions with fire
The COMTF April 2020 newsletter reports the growing threat to manzanitas from P. ramorum. The genus Arctostaphylos includes more than 100 species of evergreen shrubs and small trees. Nearly half are classified as rare, threatened, or endangered. The center of diversity is in the San Francisco area – which overlaps with the area intensely infested by P. ramorum. At least 18 manzanita species support the pathogen. Koch’s postulates have been completed on seven of the most recently detected hosts, and are under way for two others. I am grateful to the California Department of Food and Agriculture for carrying out these studies; without them, APHIS would not recognize the plants’ host status. (Despite requiring completion of Koch’s postulates, APHIS does not fund these studies.)
A study of the interaction between P. ramorum and fire in California (October COMTF newsletter and Simler-Williamson et al.) found that frequently-burned forests were less likely to be invaded by the pathogen, had lower incidence of host infection, and lower occurrence and density of epidemiologically-significant hosts. The authors think that the fire-caused loss of tall, mature California bay laurel trees might temporarily dampen pathogen transmission and “release” susceptible species from significant inoculum pressure.
The June COMTF newsletter reports that the forest infestation in Oregon continues to spread. During spring 2020, Oregon detected 15 new P. ramorum infestations at or beyond the Oregon Generally Infested Area (GIA). The October newsletter reports that 38 stream drainages both inside and outside the SOD quarantine area were baited, and one at the northern boundary of the quarantine area was positive for P. ramorum. The Oregon Department of Forestry installed additional stream baits in the drainage to pinpoint the infestation, and plans a stream survey for the area. Planned eradication efforts have been impeded by funding cuts caused by Covid-19-related falls in tax receipts.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Press, C.; Fieland, V.; Creswell, T.; Bonkowski, J.; Miles, L. and Grünwald, N.J. 2020 (First Look). First report of the NA2 clonal lineage of Phytophthora ramorum in Indiana. Plant Disease. https://doi.org/10.1094/PDIS-12-19-2543-PDN.
Simler-Williamson, A.B.; Metz, M.R.; Frangioso, K.M. and Rizzo, D.M. 2020. Wildfire alters the disturbance impacts of an emerging forest disease via changes to host occurrence and demographic structure. Journal of Ecology. Early View. https://doi.org/10.1111/1365-2745.13495
Port of Mobile, Alabama Photo by Port of Mobile Authority
In August and September I blogged about the rapid increase in volumes of imports from Asia, especially China, in 2020. At the time, the information available to me focused on the Pacific coast ports, especially Long Beach and Los Angeles.
In the earlier blogs, I mentioned three concerns:
1. Had the collapse in trade and travel during spring 2020 so reduced user fees that Department of Homeland Security Bureau of Customs and Border Protection (CBP) had to furlough Agriculture Quarantine Inspectors? AQI inspections provide important incentives for importers to follow U.S. and international rules to reduce the risk that pests will be present in imports, for example, in wood packaging.
2. The list of imports from China in the first half of 2020 includes $1 billion worth of nursery stock. This is down about 7% from 2019. However, from the perspective of preventing plant diseases and pests, these imports continue to be high risk and are still not adequately addressed by U.S. policy.
3. Other Asian regions are gaining in import share. Thus we can expect to see more pests arriving from countries other than China, like Vietnam.
Cutbacks in Numbers of Inspectors?
CBP staff have told me that they are shifting AQI inspectors from covering incoming passengers – which are still far fewer than before the Pandemic – to inspecting cargo. By doing so, CBP has avoided cutting back on the total number of inspections of imported goods and associated wood packaging.
This is fortunate since Congress has not passed a new Covid-19 financing bill that might have included an increase in the appropriation for DHS CBP. The Continuing Resolution currently in effect funds the government only until December 11. So we have another chance to ask for an increase in appropriated funds for CBP (and APHIS!) for the remainder of Fiscal Year 2021 (which ends on October 1, 2021).
Volumes of Imports from Asia – Especially China
As I reported in the earlier blog, while U.S. imports from China declined significantly in 2019 and early 2020 compared to earlier years, by the summer imports had rebounded — more than doubled (by value) between March and July.
Shifts in U.S. Ports
According to the Journal of Commerce, there is a gradual shift away from the twin ports of Los Angeles and Long Beach in the proportion of imported goods entering the country. LA-LB handled 37.7% of the loaded twenty-foot equivalent containers (TEUs) entering the United States in 2018. This fell to 33.5% in July 2020. The initial reason was a decrease in imports from East Asia (including China, Hong Kong, Japan, South Korea, and Taiwan) compared to Southeast Asia, Europe, then South America and, finally, South Asia (primarily India).
Other source regions – e.g., the Caribbean, Middle East, Pacific, Africa, and Atlantic – were all below 2% of total numbers of TEU in all three years, and changed minimally over this period.
Another reason for the shift in ports utilized by importers is congestion and delays at North American Pacific coast ports, especially Los Angeles-Long Beach. U.S. imports from Asia moving through LA-LB increased 22% in both September and August from the same months last year – 828,880 TEU in September after 832,210 TEU in August.
Congestion is also a problem at the Canadian ports of Vancouver and Prince Rupert – which have actually seen small decreases in numbers of incoming containers.
One result is a small but significant shift to Gulf Coast ports, which have become more accessible through the widening of the Panama Canal in 2016. Before the Canal was widened, these ports handled less than 3% of total US imports from Asia. In the first nine months of 2020, US Gulf ports handled 608,387 TEU from Asia – or 5.2% of total US imports from Asia. This was a 5% increase from the same period last year.
These ports, stretching from Houston to Tampa, benefit from easy and relatively cheap rail transport to inland U.S. and even Canadian cities. Another factor is the heavy presence of Walmart – which has major distribution centers in Mobile and Houston.
The Gulf coast ports are expected to expand their importance as gateways for Asian imports as ocean carriers add more capacity between the two regions and ports upgrade and expand. New Orleans and Houston plan major expansions. Port Tampa Bay notes its proximity to markets around the Southeast. Already, import volumes into Tampa during the first nine months of 2020 were nearly double the prior year’s level. Tampa hopes to double its capacity over the next five years.
U.S. imports from Asia in October were 22.6% higher than a year ago. Imports through the East and Gulf coast ports jumped 14.6% and 48.4% from September 2020. Houston and Baltimore saw the greatest increases since September. There were also shifts in Pacific ports. Still, the Los Angeles-Long Beach port complex handled 49% of total US imports from Asia in October 2020.
Pest Risks to the Gulf Coast from Southeast Asia
Rising volumes of imports into the Gulf Coast present new opportunities for non-native insects and pathogens. The warm, wet climate of the region might be far more suitable to some insects and pathogens from tropical and subtropical Asia than the dry climate of southern California (except for areas that are irrigated artificially, such as golf courses, parks, and plant nurseries!).
redbay grove killed by laurel wilt; Photo by Scott Cameron
Already, the redbay ambrosia beetle and its associated pathogenic fungus has decimated native redbay and swamp bay trees and now threatens sassafras (see write-up under the “invasive species” tab here.)
Another Southeast Asian ambrosia beetle – the polyphagous shot hole borer with its associated pathogenic fungus – might also find the Gulf Coast states more inviting than southern California. In California, it is causing the greatest damage to trees that are artificially irrigated. Numerous tree species native to or grown in the Gulf states are known hosts, e.g., box elder, sweetgum, and southern magnolia. (PSHB is described under the “invasive species” tab here.) Both ambrosia beetles apparently were introduced via wood packaging material.
Southeast Asia is also the place of origin of other pathogens which – in this case – would more probably be introduced on imported plants rather than wood. These include the numerous species of Phytophthora recently detected in Vietnam.
As this region receives more goods from Asia, and as those goods arrive more rapidly so more likely to arrive alive, it is imperative that all stakeholders increase their vigilance to detect new invaders. And that they join others pressing for improved policies aimed at preventing introductions.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report here.
In 2017 I blogged about a study by Hanno Seebens and 44 coauthors that showed that the rate of new introductions of alien species has risen rapidly since about 1800 – and showed no sign of slowing down (a reference to the full article is at the end of this blog). Here’s a brief recap, followed by a 2020 update by Seebens and colleagues.
In 2017, Seebens et al. analyzed a database covering 45,813 first records of 16,926 alien species established in 282 distinct geographic regions. The year with the highest number of reported new detections was 1996 – 585, or an average of more than 1.5 sightings per day.
The authors found that the adoption of national and international biosecurity measures during the 20th Century had slowed introductions – but not sufficiently. Numbers of reported new introductions of fish and mammals had decreased since the early 1950s. However, first recorded introductions of vascular plant species remained high, and introductions of birds and reptiles also continued to rise, largely as pets in countries with strengthening economies.
For taxa introduced primarily accidentally on transport vectors or as contaminants of commodities (e.g., algae, insects, crustaceans, molluscs and other invertebrates), they found a strong correlation between their spread and the market value of goods imported into the region of interest – existing biosecurity regimes had not slowed down the accumulation of these alien taxa.
As a consequence, the authors expected that the numbers of new alien species would continue to increase.
As you are aware, since 2015 I have posted 15 blogs about the continued detections of tree pests in wood packaging, which remains one of the major pathways despite the international regulation ISPM#15. I have found it harder to track insect and pathogen introductions on imported plants, but it surely continues apace.
2020 Study Projects Continuing Rise in Introductions, Especially Arthropods
Hanno Seebens and a smaller set of coauthors (see full reference at the end of this blog) have now produced an estimate of probable introduction rates in the future. They looked at taxon–continent combinations for seven major taxonomic groups and eight continents (excluding Antarctica).
They found an overall increase in established alien species between 2005 and 2050 of 36%.
The study predicted that by the mid-21st Century, there will be distinct increases in alien species numbers, particularly for Europe, but also for Temperate Asia and North America, and for invertebrates in all regions. Europe ranked highest in absolute numbers of new alien species (~2,543; a 64% increase). Temperate Asia was projected to receive about 1,597 species (a 50% increase); North America about 1,484 (a 23% increase); South America about 1,391 (a 49% increase); and the Pacific Islands about 132. Only Australasia could expect a slower rise in introductions. The predicted trajectories of alien species numbers were surprisingly similar for mainland and island regions across taxonomic groups.
Invertebrates showed the highest relative increases. Rates of new detections of alien species were projected to accelerate for arthropods other than crustaceans worldwide, especially for North America (!). The study also projected higher relative increases for aquatic vascular plants and terrestrial insects
All drivers of introduction and invasion are predicted to intensify in the future. This is despite adoption of increasing numbers of countermeasures in recent decades. Most countries’ capacity to proactively counter the rising tide of invasive species is still poor. Furthermore, the principal drivers – intensification of trade and transport, land-use change, and access to new source pools – is expected to continue operating as now – “business as usual”.
spotted lanternfly Holly Ragusa, Pennsylvania Department of Agriculture
Current Status of “New” Detections
Seebens et al. (2020) relied on the Alien Species First Records Database for first detection records up to 2005. More than half (54%) of the first-detection records in the database are vascular plants. Arthropods other than crustaceans made up 28% of the total, birds 6%, fishes 4%, mammals 3%, molluscs 2%, and crustaceans 2%. The 2020 study confirmed the earlier finding that the observed first-record rates of mammals changed at around 1950 from an increasing to a decreasing trend. Finally, the total numbers of non-native species in the Database is much lower in aquatic habitats. (The authors do not discuss whether this reflects actual introductions or gaps in reporting.)
In the database, Europe recorded 38% of all first records, North America 16%, Australasia 15%, South America 9%, Temperate Asia 9%, Africa 6%, Pacific Islands 5% and Tropical Asia 2%.
A comparison to the immediate past (1960-2005) showed that the rates of emerging non-native species were projected to accelerate during 2005-2050, especially for arthropods. As I noted above, North America is predicted to have high increases in absolute numbers. Increases are also predicted for birds. Declines are predicted for mammals and fishes.
Asian giant hornet; photo from University of Florida Department of Entomology
Projected increases for Australasia were consistently lower than in the past.
Caveats:
1) The authors assumed that past patterns of alien species accumulation will continue in the future. They did not attempt to predict efforts to strengthen biosecurity regulations and mitigation strategies.
2) Projections were calculated in the absence of data on many underlying drivers for the historic periods and some taxonomic groups. However, observed trends of newly-detected alien species numbers during the 20th century were surprisingly stable despite distinct political and socio-economic changes.
Seebens and colleagues conclude that implementation of targeted biosecurity efforts can reduce the numbers of new alien species becoming established. However, a significant decrease in rates of alien species numbers on a large scale can only be achieved by a coordinated effort that crosses political borders.
Seebens, H., S. Bacher, T.M. Blackburn, C. Capinha, W. Dawson, S. Dullinger, P. Genovesi, P.E. Hulme, M. van Kleunen, I. Kühn, J.M. Jeschke, B. Lenzner, A.M. Liebhold, Z. Pattison, J. Perg, P. Pyšek, M. Winter, F. Essl. 2020. Projecting the continental accumulation of alien species through to 2050. Global Change Biology. 2020;00:1 -13 https://onlinelibrary.wiley.com/doi/10.1111/gcb.15333
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
dead ash along Accotink Creek, Fairfax County, Virginia photo by F.T. Campbell
As we all know, the emerald ash borer (EAB) has killed millions of ash trees in its invaded range across eastern North America. However, field studies have detected robust regeneration of ash seedlings and saplings in various invaded areas. Ward et al. 2021 (full citation at end of blog) set out to determine whether this regeneration will result in recovery of mature ashes that can perform their ecological role. They conclude that it will not. Instead, they say, the EAB invasion will probably alter successional patterns and composition of large areas of naturally regenerating forests, causing a cascade of ecological impacts in ash-containing ecosystems
Ward and colleagues used USDA Forest Service Forest Inventory and Analysis (FIA data) to quantify ash recruitment and regeneration across the entire eastern United States. Theirs is the first study to evaluate trends across the region, rather than specific locations or stands. They related the FIA recruitment data to EAB spread, as measured by USDA Animal and Plant Health Inspection Service’ (APHIS) record of the first EAB detection in each county.
FIA inventories in 2002-2007 and 2013-2018 show large numbers of ash seedlings and saplings in counties invaded in the first wave of invasion, 2002–2006. These areas had higher densities of both seedlings and saplings than plots in other counties. The earliest-invaded counties were in areas that had extraordinarily high densities of ash before the EAB invasion, so the numbers of seedlings and saplings probably reflected that abundant seed source.
However, by the 2013-2018 inventory ash trees in the smallest overstory class (12.7 cm dbh) were dying at faster rates than they were recruited from seedlings or saplings in all 362 counties recorded by APHIS as EAB-infested before 2013. Ward and colleagues found these negative population trajectories on plots that have been invaded for more than about 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range.
Some U.S. Forest Service biologists are more optimistic about ash recovery in response to biocontrol of the EAB. See their podcast here.
In the risk of functional extinction, ash trees are unfortunately not unique. The authors note similar impacts from the invasion of the hemlock woolly adelgid and beech bark disease.
Data Reveal History of Invasion (spread)
Ward and colleagues focused on the risk of mortality for young ashes as they developed from seedlings to saplings, and, eventually, to overstory trees. The youngest “overstory” trees are 12.7 to 17 cm dbh. FIA data show that even the largest trees in this class are 3 cm smaller than trees that produce seeds.
Mortality was initially uniformly low – less than 2.1% — as measured by the first FIA inventory (2002–2007). This is not surprising because EAB was detected only in 2002, and then in only few counties. (EAB had probably been present for a decade before it was detected.)
By the 2013-2018 FIA inventory, mortality had quadrupled to 8–11% in counties invaded during the 2002–2006 period. In the counties invaded during the 2007–2012 period, morality also rose to 3-5%. Both measurements included all diameter classes. Annual mortality rates in the FIA 2013-2018 inventory were still highest for the counties invaded during 2002–2006 except for the largest trees (those greater than 40 cm dbh). By the time of the 2013-2018 FIA survey, overstory ash densities near the epicenter had since declined substantially. They had been nearly eliminated in some counties in southeastern Michigan. There were still sufficient numbers of smaller trees in the region to exhibit an elevated mortality rate – more than 10% per year in several counties in Michigan, Indian, and Ohio. By contrast, in the most recently invaded areas – those counties recorded by APHIS as infested after 2013 – there was very little change in ash densities compared to the 2002-2007 period. This is hardly surprising since it takes years for mortality to reach levels observable by the FIA process.
dead ash on edge of Pohick Bay, Fairfax County, Virginia photo by F.T. Campbell
Considering trees just entering the overstory category (those with diameters of 12.7 cm dbh), annual mortality increased substantially across the region. Between the first FIA inventory (conducted in 2002-2007) and the second inventory (conducted in 2013-2018), their average annual mortality rose more than four-fold, from 0.08 trees per ha to 0.37 trees per ha. By 2013-2018, recruitment in the 2002–2006 invasion cohort was about 50% less than tree mortality levels; recruitment and mortality were about equivalent for the counties invaded in the 2007–2012 period. Recruitment was [still] significantly higher than mortality for the counties recorded as invaded in 2013–2018. However, Ward and colleagues expect mortality rates of this cohort to accelerate over the next five to 10 years – even in areas with lower ash densities.
Ward and colleagues note that many of the young ash trees were dying before they could reach reproductive age – which they estimated to be about 20 years with a dbh of about 20 cm.
As the invasion progresses and hosts are depleted, mortality rates could slow, but, for ash to persist, it is critical that sufficient numbers of trees reach reproductive age before succumbing to residual EAB populations.
Other factors that might influence ash include competition with trees in other genera. The biocontrol agents now becoming established in young ash forests might increase the likelihood of ash persistence. Still, seed production and seedling survival will need to be frequent and widespread if they are to offset expected mortality. Resilience might also vary depending on individual species’ vulnerability to changes in the climate and to EAB (green and black ash are more vulnerable than white ash).
SOURCE
Ward, S.F., A.M. Liebhold, R.S. Morin, S. Fei. 2021. Population dynamics of ash across the eastern USA following invasion by emerald ash borer. Forest Ecology and Management 479 (2021) 118574
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Asian giant hornet; photo from University of Florida Department of Entomology
Asian giant hornet (AGH) (Vespa mandarinia) is the world’s largest hornet, reaching sizes of 1.5 – 2 inches long. Its native range includes much of Asia. While media attention has focused on the hornet’s frightening size, the real threat is to honey bees (Apis spp.) and – especially – to the many important crops that bees pollinate.
Over the past year or so, several detections of the Asian giant hornet have been found in the Pacific Northwest – in British Columbia and Washington State. Four of the sites are within a few miles of each other. Two others are separated by miles of open water from the mainland sites. As of mid-October, 18 hornets had been detected in Washington State.
USDA’s Animal and Plant Health Inspection Service (APHIS) has partnered with the Washington Department of Agriculture to try to eradicate the hornet – which will not be easy! However, the Canadian Food Inspection Service (CFIA) has decided not to designate the hornet as a quarantine pest. This decision seems to threaten divergent approaches to the bioinvader. Fortunately, the Province of British Columbia is trying to eradicate its populations – so perhaps the diverging federal approaches will not result in facilitating the hornet’s establishment and spread.
Where the Hornet Is Known to Be
The first detected outbreak of the Asian giant hornet was in Nanaimo, British Columbia – on Vancouver Island. A single hornet was detected in August 2019. [A Canadian commenter said in March 2021 that this turned out to be a different species, V. soror.] A nest was detected in September and destroyed by local beekeepers and BC government officials. However, another hornet was found on the mainland – in White Rock, B.C. – in November 2019 [CFIA Decision Document]. In 2020, there have been several unconfirmed sightings in the Cowichan Valley on Vancouver Island (van Westendorp, pers. comm.).
Meanwhile, beekeepers discovered two AGH outbreaks in Whatcom County, WA, on the U.S. side of the border. These discoveries were in December 2019 and May 2020. There were other, unconfirmed reports in both Washington and British Columbia. [USDA APHIS Environmental Assessment (EA)] Indeed, later in 2020, Washington reported a few more sightings — in the Birch Bay area, just south of Blaine and at a site about eight miles east of Blaine (van Westendorp, pers. comm.)
Three of the hornets found in spring 2020 were mated queens (Zhu et al. 2020), which means at least one colony successfully reproduced last year. One of the mated queens was the second detection in Whatcom County – in Custer, Washington. One article said that the locations of this spring’s queens meant either that the new queens travelled up to 35 kilometres (about 22 miles) before founding their nests or that they came from more than one colony. Either way, it probably means that giant hornets could spread faster than initially thought.
White Rock, BC and Blaine, Washington are a few miles apart on the Canada-U.S. border. Langley is 12 miles to the northeast of White Rock – in the Fraser Valley. Custer is 7 miles southeast of Blaine. Birch Bay is 5 miles south of Blaine. The most recent detection is 8 miles east of Blaine. So all these detections are in close proximity and might represent spread from a single introduction site – or maybe not!
Nanaimo and the Cowichan Valley are on Vancouver Island, which is separated from the other locations by a significant distance and open water. The two island sites are about 30 miles apart. They surely represent one or more separate introductions.
One study found that a single hornet collected from Blaine, Washington differed genetically from a single hornet collected at Nanaimo on Vancouver Island. This suggests separate introductions. However, too little is known about the hornet’s genetic variability across Asia to allow conclusions about possibly separate origins (van Westendorp, pers. comm.; Wilson et al. 2020).
Areas at Risk
The area at risk is potentially much broader than the Pacific Northwest. APHIS’ initial analyses, based on plant hardiness zones, indicated that the hornet could thrive in virtually all the lower 48 states. APHIS’s Environmental Assessment did not address vulnerable areas in Canada or – apparently – in Hawai`i.
Zhu et al. (2020) carried out an assessment of areas most at risk and the hornet’s potential rate of spread. They found that areas with warm to cool annual mean temperature, high precipitation, and high human activity were most likely to be suitable for the hornet. Areas meeting these criteria are found across western and eastern North America, Europe, northwestern and southeastern South America, central Africa, eastern Australia, and New Zealand. Most of central North America and California are less suitable.
Spread could be rapid in the Pacific Northwest: they predicted that the hornet could reach Oregon in 10 years, eastern Washington and British Columbia within 20 years. This prediction is based in part by experience with the invasive congener V. velutina in Europe; it has expanded by 78 km/year in France, 18 km/year in Italy.
Oregon is relying on beekeepers to detect the hornet, which they expect will arrive even earlier than 10 years from now. The Oregon Department of Agriculture has suffered severe budget cuts because of the Covid-19 crash in state tax collections, so the program is trying to save money. As of the beginning of October, none of the hundreds of citizen reports has been a Vespa of any species (J. Vlach, Oregon Department of Agriculture, pers. comm).
Pathways of Introduction
It is not known how the hornet reached North America. Reports from other countries indicate that they can hitchhike in shipments of empty plant containers, or in the straw in which the containers are packed. In addition, some Asian cultures regard the hornets as delicacies, so deliberate importation is possible. Both APHIS and the Canadian Food Inspection Agency (CFIA) have intercepted such shipments (CFIA Decision document; USDA APHIS PPQ New Pest Response).
The Threat
The AGH typically feeds on a variety of terrestrial invertebrates including beetles, mantids, caterpillars, and spiders (EA). During the spring and summer, hornets attack their prey singly. However, in the Aautumn, hornet workers carry out mass attacks against other social Hymenoptera – including other species of Vespa, yellowjackets (Vespula spp.), various paper wasps (Polistes spp.), and honey bees (Apis spp.). Commercial honeybee colonies are typically lost when attacked en masse. They are especially vulnerable because they are more concentrated than wild bee colonies. [EA]
Commercial honeybee colonies pollinate a wide variety of crops, including tree fruits, cane fruits (berries), tree nuts, tomatoes, and even potatoes. Supplies of beef and milk might also be at risk because alfalfa hay is pollinated by bees. Of course, honey production would also be threatened. As USDA APHIS has stated, if the Asian giant hornet spreads it would become a new stress on top of the multiple existing causes of honeybee decline.
Also, there is a direct threat to people. The AGH has a painful sting that can result in anaphylaxis, cardiac arrest, and other complications in susceptible people. Officials emphasize that most people will not be at risk of stings. However, beekeepers are – their usual Personal Protective Equipment (PPE) is not adequate to ward off the hornet’s sting [APHIS EA & New Pest .
APHIS’ programmatic Environmental Assessment notes that the hornet might also pose a threat to vertebrates that nest in ground burrows and decayed trunks and roots near the ground. Burrows chosen by female hornets for nest construction can be surprisingly large, up to 60 cm (24 inches) in diameter. The EA notes that, in Washington State, badgers, marmots, ground squirrels, and other small mammals use dens or burrows. Among these, four pocket gophers and the American wolverine are federally listed under the Endangered Species Act in Washington State. [For a list, see the environmental assessment.] The EA does not discuss whether cavity-nesting birds might also be affected – although the hornets do prefer hollows near or at ground level. The authors of the EA expect vertebrates to abandon any burrows used by the hornet, so they would be displaced rather than harmed by pesticides applied by the program described below.
APHIS program
APHIS and the Washington State Department of Agriculture (WSDA) have begun an eradication program. I think eradication will be challenging because it will be very difficult both to find nests and to destroy them.
Hornets nest typically in forested areas or urban green spaces. There are lots of suitable places in the Pacific Northwest! These wooded areas are interspersed with farms, orchards, and settlements that will provide vulnerable insects as food sources.
Nest destruction involves excavating a hole two meters by two meters. This digging must be in woodlands, often right next to trees.
The key to successful eradication is finding and destroying the nests before they produce reproductive females and males – in autumn. Nest detection will be carried out as follows [EA]:
Starting in April, the agencies bottle traps in trees near the 2019 detection points. The traps are baited with a solution of rice cooking wine and orange juice to attract the worker bees. (The rice wine is added to discourage honeybees from visiting the trap.) Traps catches help define areas where nests are located.
WSDA successfully tracked radio-tagged workers to a nest in mid-October. That nest was in a tree hollow, not underground.
WSDA scientists think there were approximately 200 queens in that single nest. Two were vacuumed out during the initial extraction. Inside the nest they found 76 emergent queens and 108 capped cells with pupae that they believe were also queens. Three more queens were trapped in a bucket of water. This nest had approximately 776 cells; large nests can have up to 4,000. WSDA believes there are other nests in the area; they continue to search.
APHIS’ original plan to use pesticides to kill hornets in the nest has been dropped. Washington plans now to use vacuum extraction followed by introduction of CO2 and excavation of the nest. Washington has also not decided whether to deploy traps with the pesticide fipronil (S. Spichiger, pers. comm.)
WSDA has also asked members of the public to set out homemade hornet traps, and to report any suspicious sightings.
Canada Takes Opposite Tack
The Canadian Food Inspection Agency (CFIA) announced in February 2020 (CFIA Decision Document) that it will not attempt to regulate the Asian giant hornet as a quarantine pest for Canada. Therefore, CFIA will place no restrictions on the import or movement of any commodities that may harbor the Asian giant hornet. CFIA will, however, require permits for deliberate importation of the hornets.
CFIA’s reasoning appears to focus on two factors:
The hornet is an indirect threat to plant health (since AGH attacks pollinators. CFIA has traditionally regulated quarantine pests based primarily on significant direct threats to plant health.
Under the international phytosanitary system, countries that designate an organism to be a quarantine pest must put in place the necessary measures to prevent its entry into the country, as well as officially control the pest when present. CFIA states that “High uncertainties about the pathways of entry puts into question the ability to manage this risk, and ultimately the ability and feasibility of regulating V. mandarinia as a quarantine pest.”
Neither APHIS nor CFIA has authority to regulate threats to human health.
Detection and Eradication Efforts in British Columbia (information from van Westendorp, British Columbia Ministry of Agriculture)
In 2020, British Columbia has focused on detection surveillance. Target areas include vicinity of Nanaimo on Vancouver Island; Fraser Valley from White Rock in the West to Langley/Aldergrove in the East (along the US border); and after several credible (but non-verified) sightings, the Cowichan Valley on Vancouver Island. Because of resource limits, the surveillance effort has sought to engage local governments, border agencies, First Nations, forestry & mining companies, farmers, and beekeepers. The ministry also placed numerous bottle traps and encouraged 170 beekeepers in the Fraser Valley to install and monitor traps in their apiaries.
So far, only one AGH specimen has been sighted or collected in the three British Columbia survey areas during 2020 – the single specimen at Langley detected in May. However, the several detections along the U.S. side of the border (see above on recent detections) has spurred BC officials to intensify survey efforts in the Fraser Valley (van Westendorp). A specimen was collected adjacent to the US border in mid-October just north of the multiple detections in the US, and South of the Langley detection last spring (S. Spicher, pers. comm.).
British Columbia will continue to monitor well into the fall season and resume our surveillance in 2021 and 2022 (van Westendorp).
Hornets are clearly able to be transported and introduced. Vespa ducalis was detected in Vancouver, BC in 2019 and in Texas in 2020. Vespa velutina has become established in Europe (J. Vlach, Oregon Department of Agriculture, pers. comm).
USDA APHIS Asian Giant Hornet Control Program in Washington State Final Environmental Assessment—July 2020
USDA AHIS PPQ New Pest Response
van Westendorp, Paul. British Columbia Ministry of Agriculture, pers. comm.
Wilson, T.M., J. Takahashi, S-Erik Spichiger, I. Kim, and P. van Westendorp. 2020. First Reports of Vespa mandarinia (Hymenoptera: Vespidae) in North America Represent Two Separate Maternal Lineages in WA State, US, and BC, Canada. Annals of the Entomological Society of America · October 2020
Zhu, G., J. Gutierrez Illan, C. Looney, and D.W. Crowder. 2020. Assessing the ecological niche and invasion potential of the Asian giant hornet. PNAS Latest Articles ECOLOGY
