Confirmation of failures of the international phytosanitary system

California sycamore infested by PSHB; photo by Bea Nobua

Lantschner et al. (2026; full citations at the end of this blog) review global spread of an ambrosia beetle species complex, the polyphagous shot hole borer (PSHB, Euwallacea fornicatus). This complex has caused significant damage in southern California and is now poised to raze unique plant communities in South Africa, Western Australia, and possibly elsewhere. Dell, Xu, and Chi (2026) say that introductions of these species pose serious challenges to global biosecurity programs and forest health management.

Unfortunately, neither Lantschner and colleagues nor Dell, Xu, and Chi, nor even Pennisi’s summary of the situation in Science (2026) suggests the kind of bold changes to the international phytosanitary system needed to prevent repetitions of this disaster.

Ambrosia beetles are especially suitable study subjects for analyzing international movement of non-native species. Some reasons result from the beetle’s biology: they have broad host ranges, close associations with pathogenic fungal symbionts, cryptic biology, specialized breeding systems which allow extremely low populations to start an infestation, and the ability to establish across diverse climatic regions. Other reasons stem from the beetles’ frequent association with international trade in timber and/or ornamental plants.

PSHB’s Impact in California

California has been invaded by three species of Euwallacea — Euwallacea fornicatus s.s., Euwallacea kuroshio, and Euwallacea interjectus. The beetles vector three previously undescribed species of fungus that cause disease in host trees: Fusarium euwallacea, Fusarium kuroshium, and Fusarium floridanum.

Euwallacea fornicatus s.s. (polyphagous shot hole borer, or PSHB) came to attention in late winter 2012, when a new insect/pathogen complex was discovered causing damage to avocado trees in residential neighborhoods and a commercial avocado grove in Los Angeles County, California. Later studies determined that the beetle and its associated fungus had been in California since at least 2003 (Eskalen et al. 2013).

Over the nearly 15 years since its discovery, the PHSB/pathogen complex has spread across much of southern California. Populations are established in Orange, San Diego, Los Angeles, Riverside, San Bernardino, Ventura and Santa Barbara counties.   The separately introduced species Kuroshio shot hole borer (KSHB) was discovered in late 2013 in San Diego County. It has since spread to Mexico. Californians now track the two species as one; a map showing their current known distribution is posted here.

Box elder (Acer negundo) from Traité des Arbres et Arbustes que l’on cultive en France en pleine terre (1801–1819) by Pierre-Joseph Redouté. Original from the New York Public Library. Digitally enhanced by rawpixel.

Certainly a wide range of tree species face a challenge – as do their associated natural or anthropogenic systems. Nearly 600 plant species in more than 30 plant families are known hosts of PSHB worldwide (Ceriani-Nakamurakare, Johnson and Gomez, 2023). In southern California specifically, 65 woody species are able to support reproduction of both the beetle and the pathogen. The preferred and most susceptible hosts are several species in the maple (Acer), Parkinsonia, plane (Platanus), oak (Quercus), and willow (Salix) genera. Box elder (A. negundo) is so susceptible that it is considered a sentinel tree. The following additional native species are also hosts: big leaf maple (Acer macrophyllum); California sycamore (Platanus racemose); three Populus species, P. fremontii (Fremont cottonwood), P. nigra (black poplar), and P. trichocarpa (black cottonwood); Valley oak (Quercus lobata); and three willows – black (Salix gooddingii), red (S. laevigata) and arroyo (S. lasiolepis). Three more oaks – coast live oak (Q. agrifolia), canyon live oak (Q. chrysolepis), and Englemann (Q. engelmannii) – are less susceptible; they suffer branch dieback rather than death.

Given PSHB’s wide host range, it is not surprising that Lynch et al. (2025) found that regions at risk of future invasion are determined largely by climate rather than host abundance. Areas where temperatures are sufficiently warm to allow the beetle to pass through at least five generations per year include parts of southern California, drier regions of the San Francisco region, and portions of the Central Valley. A risk map for California is available here.

The E. fornicatus and E. kurosio combined outbreak has killed large numbers of trees in southern California’s coastal counties – although I have been unable to find an estimate.  Meanwhile,  additional outbreaks have been detected. The PSHB was found in the San Jose area in 2023. This location is close to the state’s Central Valley – where vulnerable almond, pistachio, and other crops grow (Pennisi, 2026). A third, related species, E. interjectus, also turned up. See a map of distribution of all three Euwallaceae established in California here.

A dozen years after their presence was detected, Dr. John Kabashima led a lobbying effort that persuaded the state legislature to fund a collaborative program comprising an action plan, five research initiatives, and a comprehensive outreach and education strategy across the state (Dell, Xu, and Chi). These funds ran out at the end of 2025, while the infestation continues.

As of the first half of 2026, official monitoring projects were reported to be under way in four of the seven invaded counties, Los Angeles, Orange, Riverside, and San Bernardino. This effort is now being cut back because state funding supporting it has expired. For example, Los Angeles County carried out surveys in 240 parks in 2025, but planned to survey only 146 in 2026. While in most parks the infestations were described as light or moderate, five parks with heavy infestations were detected in 2025; trees in a sixth park were reported to be recovering.

Attention continues from the California Invasive Species Advisory Committee, Los Angeles and Orange County Master Gardeners Emerging Tree Pests Groups, University of California Agriculture and Natural Resources (UC ANR) representatives, UC Cooperative Extension from various counties, and Cal-Fire. These organizations seize opportunities to educate the public about the shot hole borers’ impacts. 

Dr. Paul Rugman-Jones of the UC Riverside Department of Entomology is studying possible biocontrol agents. In early 2026 he was working w/ APHIS to set up research colony of Phymastichus nudusdraco, a wasp native to Taiwan that parasitizes PSHB there. He and a postdoc continues surveys on that island and elsewhere in Southeast Asia. Dr. Rugman-Jones is also searching for potential natural enemies already established in southern California.

From Asia to a World-wide Pest

The polyphagous shot hole borer has been detected in nine countries on five continents since 2000 (Lantschner et al. 2026). Many of these introductions have occurred since stricter biosecurity measures, i.e., International Standard of Phytosanitary Measures #15, came into force with the purpose of reducing introductions of insects associated with wood packaging material.

By combining data on the distribution of the species’ 36 haplotypes, phylogenetic relationships and dates of first detections, Lantschner et al. (2026) have identified seven independent introduction events of E. fornicatus: to the continental United States, Hawai`i, South America, Central Europe, Spain, Türkiye, and South Africa. I am unsure why this list does not include the introduction to Israel, detected in 2009.  

Lantschner et al. (2026) suggest two contradictory explanations for this explosive spread. On one hand, beetle populations in the species’ native Asian range might have increased recently. On the other, higher trade volumes from these countries have opened new pathways for transport. I favor the second explanation since exports from China have risen from less than $500 billion in 2003 to approximately $4 trillion in 2025. Exports from Vietnam rose from about $22 billion to $500 billion over the same period.  

Lantschner and colleagues compare the PSHB’s range of introduced populations to the more restricted locations invaded by another species in the genus, E. perbrevis. They believe that the latter is more restricted to humid tropical regions. It has been introduced to several islands in Oceania, and possibly northern Australia (Queensland). Many of these countries might be less active in global trade than the countries to which PSHB has been introduced. This shield is shrinking, however, as more countries expand their trade. Lantschner et al. (2026) warn that E. perbrevis’ establishment in subtropical FL and Panama indicates it might also tolerate broader climatic conditions than previously assumed. They think that E. perbrevis populations established in Central America might expand into northern South America, including the Amazon basin and the Brazilian coast. Another area at risk is central Africa.

Neither Lantschner et al. (2026) nor Dell, Xu, and Chi (2026) discuss why other species in the genus have been introduced to fewer locations. Euwallacea kurosio and E. interjectus are also established in California, but nowhere else.  

PSHB Threatens Severe Impacts in its Introduced Ranges Other Than California

The outbreak in South Africa occupies the largest geographic region of any PSHB outbreak on Earth (Bierman, Roets, and Terblanche 2022). Dell, Xu, and Chi (2026) anticipate significant economic costs tied to the need to remove affected urban trees. The article in Science (Pennisi 2026) quotes Stellenbosch University ecologist Francois Roets as saying the long-term consequences of these forest invasions will be “substantial”.

Erythrina caffra in South Africa infested by PSHB; photo by T. Paap

In South America PSHB has spread 3,500 km along the coast since it was detected in Brazil in 2020. While local experts Ceriani Nakamurakare and colleagues (2023) mention attacks on non-indigenous landscaping favorites, Dell, Xu, and Chi (2026) report that in Uruguay a significant number of native species have proved to be reproductive hosts for the beetle.

The PSHB invasion in Western Australia is particularly worrying. The list of hosts has grown rapidly. While 69% are non-native plant species, 8.7% are regionally indigenous and another 21.3% are native to other parts of Australia. Initially authorities attempted to contain the outbreak. They spent $40 million pruning or removing 5,000 trees in the Perth region (Pennisi 2026; unclear whether the figure is in U.S. or Australian dollars). They then decided that eradication was infeasible and shifted the program to management focused on minimizing the risk of further spread. In November 2025, the National Management Group allocated $16.5 million (Australian) to this effort. The state of Western Australia committed $18.8 million for the 2025–26 period, plus $5.1 M for a tree recovery initiative (Dell, Xu, and Chi 2026).

To date, the total budget for PSHB eradication/management from all funding sources has surpassed $92 million. Under the long-term management approach, local governments and communities must assume significant additional expenses for tree removal and replacement (Dell, Xu, and Chi 2026). This team critiqued Australian officials for being slow to engage the public in PSHB detection.

According to the article in Science, the PSHB outbreak has not yet reached the habitats and hosts most likely to support establishment. There, its population could skyrocket (Pennisi 2026).

swamp banksia (Bansia littor …) one of the endemic plant species in Western Australia vulnerable to PSHB; photo by Gnagarra via Wikimedia

Upon detection of PSHB in Western Australia, authorities in the state of New South Wales (more than 3,000 km away on the other side of the continent) stepped up surveillance and risk assessment. They determined that 47% of urban trees in Sydney are susceptible to PSHB. Authorities added key PSHB hosts to the list of sentinel trees (i.e., Acer, Cupaniopsis, Ficus, Robinia). The presence of the closely related Euwallacea perbrevis has complicated efforts (Carnegie et al. 2026)

Dell, Xu, and Chi (2026) also describe damage caused by the beetle-fungus complex in Vietnam – that is, in the native range.

Future Damage

Models developed by Lantschner et al. (2026) suggest where populations of E. fornicatus might spread under the rising temperatures and shifting precipitation patterns caused by climate change. The population currently established in southern California could spread into the southeastern U.S., eastern Mexico, and parts of Central America. [I note that many proven host species are either native to or widely planted in southern U.S. states.] Populations in South Africa might spread into the northern part of temperate and subtropical regions of Africa. Beetle populations established in Spain, Israel and Türkiye might spread across the Mediterranean basin. The population in Western Australia could spread to the country’s east – as noted, NSW authorities are already alert to this possibility. Lantschner et al. (2026) raise the caveat that for many of these range expansions to occur the PSHB must cross substantial gaps of unsuitable habitat. Given that their earlier description of how frequently E. fornicatus has exploited human transport to cross oceans, I wonder that they don’t concede that this prerequisite is not likely to be a significant barrier.

Fixing the Problems

Of the references cited here, Pennisi’s article in Science has probably reached the broadest readership. However, it doesn’t discuss how governments and stakeholders can improve the international phytosanitary system. I fear readers will conclude that we are helpless to stop spread of this species or other introductions of similar organisms. The scientific papers offer some steps to improve prevention and detection of ambrosia beetles being transported by trade.

Dell, Xu, and Chi (2026) offer a welcome focus on policy-level changes. I agree with their assertion that real progress depends on more than scientists’ discoveries. They advocate shifting the international phytosanitary system from reactive eradication programs to a more proactive, adaptive, and resilient forest biosecurity systems based on the “One Biosecurity” concept. The proposed new approach will require stronger international collaboration on surveillance, diagnostic protocols, and information sharing; long-term investment in research and surveillance; and improved integration of science, policy, industry, and community. They propose a new framework to facilitate scientists’ engagement with policymakers.

However, in praising South Africa and California for utilizing citizen science and extensive community involvementDell, Xu, and Chi (2026) do not recognize how important individuals have been. In California, John Kabashima led the lobbying campaign to obtain needed government funding. https://www.nivemnic.us/?p=1275

Dell, Xu, and Chi (2026) also address scientists’ criticism of the practice of relying on lists of regulated organisms. This approach allows introduction of lesser-known species with undetermined threat status.

Dell, Xu, and Chi (2026) weigh in on details of surveillance, inspection, regulation, and management responses specific to various settings. For example, noting that only a small proportion of internationally traded wood and wood products is inspected at ports of entry, they advocate tighter phytosanitary certificates (presumably in addition to the ISPM#15 mark) and greater engagement by those in the supply chain. These authors also advocate for more intense inspection of high-risk trade pathways, enhanced surveillance and trapping around ports, and establishment of national pest surveillance programs. They expect emerging technologies e.g., molecular diagnostics, eDNA detection, remote sensing, machine learning, and AI-assisted surveillance to support major improvements in detection and management.

I applaud their attention to the demonstrated inadequacies of ISPM#15 as regards continuing introductions. To see my past advocacy on this topic, scroll down below “Recent Posts”, “Recent Comments” and “Archive” to “Categories and click on “wood packaging”.

Regarding management strategies, they describe challenges hindering use of chemical attractants and treatments, use of entomopathogenic fungi as biological control agents, and breeding trees resistant to the beetle-fungus complex. Nevertheless, they consider it essential to preserve the genetics of endangered species.

Dell, Xu, and Chi (2026) also review gaps in scientific understanding of ambrosia beetles, their host interaction and fungal symbionts. Closing these gaps is essential for developing more effective long-term management strategies. They assert that the substantial increase in funding needed to do this work is warranted given the level of damage caused by the PSHB and other ambrosia beetles.

Lantschner et al. (2026) tie their recommendations to ambrosia beetles specifically. They say that the different invasion patterns of E. fornicatus and E. perbrevis demonstrate that surveillance and management tactics must be species-specific. (This necessity adds to the complexity and resource demands of the task.) They also urge study of the PSHB’s broader microbiome, which influences beetle fitness, symbiosis stability, and invasion success. Research should also explore the extent to which environmental stressors, e.g., drought, temperature extremes, and mechanical damage, influence PSHB attacks across different environments; and whether semiochemicals have any role in insect behavior.

Finally, Lantschner et al. (2026) warn that species’ occurrence data based solely on climatic factors might not accurately reflect its possible range. This is because both biotic interactions and land-use patterns play a role in determining where a pest is present.

SOURCES

Bierman, A., F. Roets, J.S. Terblanche. 2022. Pop structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple intros into South Africa. Biol Invasions (2022) 24:2301–2312 https://doi.org/10.1007/s10530-022-02801-x

Carnegie AJ, Summerell BA, Trollip C, Tovar F, Smith DI and McDonald J (2026) Sentinel trees for early detection of non-native forest pests and pathogens in AU.

Front. For. Glob. Change 9:1801183. doi: 10.3389/ffgc.2026.1801183

Ceriani-Nakamurakare, E. A.J. Johnson and D.F. Gomez. 2023. Uncharted Territories: First Report of Euwallacea fornicatus (Eichoff) in South America with new reproductive hosts records. Zootaxa, 5325 (2), 289-297. https://doi.org/10.11646/zootaxa.f325.2.10

Dell, B., W. Xu, and N.M. Chi. 2026. Polyphagous Shot Hole Borer, a Global Threat to Forest Plantations, Green Infrastructure, and Biodiversity: Status, Challenges, and Solutions. Forests 2026, 17, 832

Lantschner, M.V., E. Ceriani-Nakamurakare, A.J. Johnson, A.I. Cognato, S.M. Smith, D.F. Gomez. 2026. Invasion history reconstruction and potential distribution of the ambrosia beetles Euwallacea fornicatus and E. perbrevis (Coleoptera: Scolytinae), two global emerging pests. J Pest Sci 99, 100 (2026). https://doi.org/10.1007/s10340-026-02070-w

Pennisi, E. 2026. Tree-killing beetle is spreading to urban forests around the world. As researchers piece together the pest’s global trek, countries are working to contain the growing threat. Science 15 July 2026

Rabaglia, R.J., S.A. Dole, and A.I. Cognato. 2006. Review of American Xyleborina (Coleoptera: Curculionidae: Scolytinae) Occurring North of Mexico, with an Illustrated Key. Ann. Entomol. Soc. Am. 99: 1034–1056.

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

Or

https://fadingforests.org

 

U.S. imports continue growing … as does risk of introductions

As I have documented in the past, wood packaging (crates, pallets, spools for cable, etc.) remains a pathway for introduction of tree-killing insects, including those that vector pathogens. Visit previous blogs describing continuing failures of the international standard by scrolling below “Comments” and “Archive” to “Categories” and click on “wood packaging”.

Because of the associated risk, I report on volumes of incoming trade containers, called “TEUs”. This acronym stands for “twenty-foot equivalent”. I focus on expanding import volumes from Asia into East and Gulf Coast ports because 1) ecological similarities between East Asia and eastern North America facilitate establishment of species from Asia into this region; 2) China has a particularly poor record of non-compliance with the international standard; 3) U.S. phytosanitary officials at eastern ports might be less prepared to handle the volume.

So what is the situation in Autumn 2026?

U.S. imports have been rising – despite tariffs, trade wars, shooting wars, and weather challenges. The following information comes from articles posted by the Journal of Commerce. Unfortunately, JOC articles are behind a paywall.

In 2025, the top nine U.S. ports handled 49.5 M total TEUs, loaded and empty, the third highest number after 2022 and 2021. People in trade expect the overall U.S. container trade to grow between 2 and 3% annually. A 3% growth rate would put total U.S. container handling (imports and exports) at just over 66 million TEUs by 2035 (Michael Angell, Oct 20, 2026).

Higher import volumes are linked to the data center construction boom (Mark Szakonyi, October 2, 2026). For example, the Port of Houston saw a 41% increase in imports of wiring, electrical transformers and switches, refrigeration equipment, and lithium-ion batteries – to 80,953 TEUs (Michael Angell, October 5, 2026).

U.S. east coast ports saw a 28% increase in volumes from Southeast Asia over the past two years (Michael Angell, Oct 20, 2026). In recent months, however, U.S. importers have shifted sourcing back to China because of easing U.S. tariffs and lower energy costs than in Southeast Asia (Mark Szakonyi, October 2, 2026.

The ports of Los Angeles and Long Beach have been handling record or near-record container volumes over the past four months as retailers responded to changing tariff deadlines and supply chain challenges caused by congestion at Chinese ports and drought-caused draft limitations at the Panama Canal (Bill Mongelluzzo, October 30, 2026).

Supply chain challenges in addition to the shallow water in the Panama Canal (which has restricted ship passages) include 13 typhoons in East Asia, some of which have forced closure of export harbors in China, Taiwan, and possibly Japan (Keith Wallis, October 23, 2026). This month devastating floods in the Four Corners area have completely disrupts rail transport from the California ports to the Midwest and East (Bill Mongelluzzo, October 27, 2026).

A looming complication is the possible strike by security personnel at Los Angeles and Long Beach (Bill Mongelluzzo, October 30, 2026; Ari Ashe, October 27, 2026).

Port of Houston

Imports from Asia to East and Gulf Coast Ports Continue to Rise

Houston saw the largest increase percentage-wise of major U.S. ports from Asia — up 11.7% from the same eight-month period (through August) in 2025. This year, 792,419 TEUs from Asia have entered Houston. (As noted above, 10% of these containers held equipment for data centers). Overall, through this period, Houston received 5% more loaded import TEUs (1.4 million) than over the same period a year ago. Other ports also received higher numbers of containers from Asia, although significantly lower percentages: Savannah imports rose by 4.5%; Los Angeles by 4%; and New York-New Jersey by 3.2%. Not all ports saw gains: Seattle/Tacoma received 14% fewer containers from Asia, Charleston 6.4% fewer, Oakland 3% fewer (Michael Angell, October 5, 2026).

Expansions Continue at East and Gulf Coast Ports

See earlier reports on these expansions by scrolling below “Comments” and “Archive” to “Categories” and click on “wood packaging”.

Container ports along the U.S. East and Gulf are in the process of or planning major expansions through the 2030s in anticipation of increasing volumes from places other than China. Projects include expanding the ports’ rail networks to reach inland markets now served mostly by the West Coast. Three projects will ramp up capacity to gradually to 6.8 million TEUs by completion a decade from now. Baltimore and Wilmington, Delaware broke ground earlier this year on their expansions. Savannah has obtained needed permits for constructing a third terminal. It also will build a new container yard. A fourth project at Norfolk will eventually add another 3.4 M TEUs to East Coast capacity. Farther in the future, Philadelphia has obtained funding to double its capacity, which would add another one million TEUs (Michael Angell, October 20, 2026). Savannah was the port of introduction of the redbay ambrosia beetle and its associated fungus as well as two conspicuous arthropods that are not forest pests, the East Asian Joro spider and yellow-legged hornet. Charleston might have been one of many ports of introduction of the Asian longhorned beetle.

dredging the Port of Savannah

Some ports have found a different, probably cheaper, way to increase capacity. The Port of New York-New Jersey is upgrading equipment so it can stack containers up to six high, thus storing a third more containers in the same space as currently. This adjustment could add another 1.5 M TEUs to the port’s current capacity of ~10 M TEUs (Michael Angell, October 20, 2026). The New York metropolitan area has been the site of numerous pest introductions, most notably the original establishment of the Asian longhorned beetle.

Asian longhorned beetle

Gulf Coast ports are also expanding. New Orleans has awarded preliminary contracts for building the Louisiana International Terminal. Houston is fast-tracking a permit for a third container terminal. These projects could add ~6.3 M TEUs in new container handling capacity on the Gulf Coast through the 2030s. More is planned. Corpus Christi has signed a lease to build its first container terminal and Mobile is dredging its harbor. These projects would raise the Gulf Coast container handling capacity to 7 million TEUs (Michael Angell, October 20, 2026).

Port expansion is not limited to the United States. The port of St. John, New Brunswick, announced it will receive C$463 million (US$330 million) from federal and provincial governments and the private sector to increase container handling capacity from 850,000 TEU to one million TEUs. The project includes dredging to allow deeper-draft ships to call more frequently, expanding port warehouses, building a new customs inspection facility, and improvements to the port’s rail infrastructure. Import volumes are growing: the 239,364 TEUs handled in 2025 was a 29% increase over 2024. Port St. John already can handle super-post Panamax ships with a 56-foot draft. (Michael Angell, October 22, 2026). Halifax was the port of introduction of three tree-killing pests: beech bark disease in the 1890s; brown spruce longhorned beetle in 1999; and beech leaf-mining weevil in 2012.

symptoms of beech bark disease; photo courtesy of Bugwood

Labor unions at Halifax and Montreal have recently signed agreements that make strikes unlikely (Journal of Commerce staff | October 23, 2026).

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

Or

https://fadingforests.org

New Zealand prepares – but perhaps not sufficiently

Metrosideros bartlettii; photo by Bodleye1 via Wikimedia Media

I rejoice that New Zealanders are exploring the risk to Aotearoa New Zealand and South Pacific islands posed by the rapid ‘ōhi‘a death (ROD) pathogens, Ceratocystis lukuohia and C. huliohia. See Marroni et al., – full citation at the end of this blog.

Marroni et al. (2026) note that several species in the genus Ceratocystis cause severe disease in native and cultivated plants following their introduction to new regions. Several of the more than 40 species in the genus have demonstrated a capacity to infect a wide range of hosts and, in some cases, to attack new hosts in novel regions.

The stakes are high. These islands are home to 54 of the 58 species in the Metrosideros genus – the genus of Hawaii’s ‘ōhi‘a lehua trees (Metrosideros polymorpha) – an endemic species of immense ecological and cultural importance. Aotearoa New Zealand alone has 12 native Metrosideros species. Four of these species are already under conservation threat. Only 31 Bartlett’s rātā (M. bartlettii) trees remain in the wild. Another species, pōhutukawa(M. excelsa), has declined 90% in abundance since Polynesian and European settlements — although it is not formally listed as threatened. (Why not?) Trees on other South Pacific islands are also apparently at risk. Metrosideros collina is widespread on these islands and is known to be susceptible to C. lukuohia. Its close relationship to both Hawaiian species and several species on the other islands suggests that related taxa across the region might also be vulnerable.

Metrosideros excelsa; photo by Ceili & Roger via Flickr

Marroni et al. (2026) worry that non-Metrosideros species (native or introduced) could also be at risk. They cite the recent finding on Kaua‘i of C. lukuohia in dead camphor trees(Cinnamomum camphora) and death of 60–100% of kiwifruit (Actinidia chinensis) in laboratory tests. So far, coffee, avocado, macadamia, mānuka (Leptospermum scoparium), and two species invasive in Hawai`i, rose apple (Syzygium jambos) and strawberry guava (Psidium cattleianum) have proved not susceptible to C. lukuohia in laboratory tests.

I applaud the New Zealanders for initiating tests of these species’ vulnerability. Preliminary results indicate that M. excelsa might be less susceptible to C. lukuohia than the Hawaiian species. M. perforata (white rātā) and M. fulgens (climbing rātā) have been found susceptible to C. lukuohia.  Pathogenicity tests are under way on additional New Zealand Metrosideros species. Marroni et al. (2026) call for screening of all Metrosideros species. They also suggest that New Zealand plant species – not just Metrosideros spp. – growing in botanical gardens or amenity plantings in Hawai’i should be monitored – application of the “sentinel tree” concept.

The scientists are also evaluating climatic factors. Although most Ceratocystis spp., including the two ROD species, are found primarily in tropical regions, some species cause disease across a broader climatic range. Models indicate that some parts of North Island are suitable now for ROD establishment. Several of the vulnerable species [M. excelsa, M. robusta (northern rātā), M. bartlettii and M. umbellata (southern rātā)] grow on that island. Low winter temperatures appear to preclude establishment on South Island at present. However, rising temperatures associated with global warming is expected to greatly expand ROD’s potential distribution to include nearly all of North Island and most of the South Island (see Figures 1a and 1b in the article). Marroni et al. (2026) say that changes in precipitation – extremely important in disease establishment – are more difficult to model. Many South Pacific Islands probably provide highly suitable climatic conditions year-round.

Worrying Conclusions About Risk

While I admire the New Zealanders’ efforts to prepare, I worry that Marroni et al. (2026)’s conclusions about the level of introduction risk are too optimistic. I fear they put too much faith in the country’s strong phytosanitary policies.

The most likely pathways of introduction are movement of infected plants, their wood, or associated soil or insects. These vectors might be moved during trade or carried by tourists.

The New Zealand Ministry for Primary Industries (MPI) applies tight requirements on imports of all nursery stock of known Ceratocystis host plants (prompted by a desire to mitigate the risk of introducing the C. fimbriata sensu lato complex). These plants must be inspected both before export and at the port of entry – including testing for the presence of a pathogen and – when indicated — treatment and/or quarantine. Any intercepted putative Ceratocystis species is subject to further diagnostic testing, and infected material is either destroyed or managed according to MPI protocols. Since 2010 New Zealand has prohibited importation of whole plants and cuttings of myrtaceous species (including the Metrosideros genus) from Australia because of the presence of Austropuccinia psidii, causal agent of myrtle rust disease. New Zealand does allow import of tissue culture plantlets from Australia, India, and the United States. Given these stringent phytosanitary requirements and the absence of plant material imported from Hawai`i, Marroni et al. (2026) concluded that the risk of introducing the two ROD pathogens is “low”.

Movement of wood could transport aleurioconidia of C. lukuohia and C. huliohia – thick-walled asexual spores that can survive in infected ‘ōhi‘a wood for at least 12 months. So all wood products derived from infected trees, including logs, timber, firewood, chips, shavings, sawdust, and other wood particles can potentially carry the pathogens. Importation of wood products is managed under seven different standards. New Zealand imports wood products primarily from North America, Southeast Asia, Pacific Islands, and Australia. Marroni et al. (2026) report that various Ceratocystis spp. have been detected on timber originating from South Pacific and Asia multiple times.

Another type of wood imports is wood packaging material – crates, pallets, spools for cable, etc. Marroni et al. (2026) call the treatments prescribed by ISPM#15 – debarking, heat treatment or fumigation – highly effective in eliminating woodborne pathogens. There have been no detections of Ceratocystis spp. on ISPM#15-compliant SWPM entering New Zealand. Consequently, Marroni et al. (2026) consider the risk of introduction via this pathway to be “low”.

Marroni et al. (2026) do express concern that ambrosia beetles could be introduced via trade in nearly any form. In Hawai`i, the beetles’ frass (wood particles, faeces and beetle fragments) is considered to be a major pathway for spread of the ROD pathogens. Frass can be carried considerable distances on the wind during storms. The frass can also be moved on tools, machinery or footwear.

The New Zealand Ministry for Primary Industries (MPI) prohibits importation of soil; this is enforced by inspection of incoming goods, machinery, containers, and visitors’ footware. They note that despite these measures, accidental intro of soil is still possible, especially via used agricultural machinery and vehicles. One study found soil contamination on 93% of sea containers and flat-rack containers arriving from several Pacific nations. This soil contained viable plant material, plant pathogens, and invertebrates.

Large numbers of New Zealanders and other Pacific Islanders visit Hawai`i. They could carry ROD propagules back to their home islands in soil on contaminated footwear, clothing, camping equipment, etc. NZ inspectors have found high incidences, counts and diversities of viable bacteria, fungi, nematodes, seeds, and several arthropods on footwear of arriving aircraft passengers. Although Marroni et al. (2026) to not explore this topic in detail, National Park Service and botanical garden websites reveal that ROD is present at several of the sites very popular with tourists. These include Kīlauea, Kīpukapuaulu, the ʻŌlaʻa rainforest, Thurston lava tube, and lower-elevation sections of the Kahuku unit of Hawaii Volcanoes National Park; the Hawaii Tropical Botanical Garden on the Big Island; and Limahuli Garden on Kauai. Overall, the authors consider the risk of introduction by this pathway to be “moderate”.

‘ohi‘a trees above trail to Thurston lava tube, Hawai`i Volcanoes National Park; photo by F.T. Campbell

If Ceratocystis lukuohia and C. huliohia were introduced to Aotearoa New Zealand or South Pacific islands, the risk of spread throughout the region seems high. There is the high volume of people and goods – including vehicles – moving among the islands. Wind storms might carry infected frass or insects from one island to another (Austropuccidia psidii is thought to have been introduced to New Zealand from Australia on prevailing winds). All these islands have feral and domestic mammals whose rooting and trampling can wound the trees, exposing them to infection by the pathogen. In New Zealand this risk is greatly exacerbated by the damage caused by the invasive Australian common brushtail possum (Trichosurus vulpecula), which feeds on tree buds and foliage and incidentally strips the bark and breaks branches.

My Concerns

  • Marroni et al. (2026) pay very little attention to the risk of introduction from the native habitats of Ceratocystis lukuohia and C. huliohia. They focus on imports and visitors from Hawai`i. These imports are dominated by aircraft and aircraft parts, scrap metals, gas turbines, seafood and beverages. The imports of primary agricultural or forestry products are in lower volumes. No nursery stock comes from the Islands.

But the Hawaiian outbreaks are caused by introduced pathogens.The native range of the species more virulent in Hawai`i, C. lukuohia, is in Latin America. The native range of C. huliohia is in Australasia! I wish Marroni et al. (2026) had explored the volume and type of imports from these regions.

  • As readers of this blog know, I do not share Marroni et al.’s (2026) sanguine evaluation of the efficacy of ISPM#15 in preventing introduction of wood-boring insects or – especially – fungal pathogens. See this blog describing the impact of polyphagous shot hole borer in one of many places where it has been introduced – perhaps via wood packaging. Or visit other blogs describing continuing failures of the standard by scrolling below “Comments” and “Archive” to “Categories” and click on “wood packaging”.
  • Most host vulnerability testing has focused on vulnerability to C. lukuohia. While C. huliohia is less virulent on Hawaii’s ‘ōhi‘a trees (Metrosideros polymorpha), I think it is unwise to assume that it will behave similarly on naïve tree species on New Zealand or other Pacific islands.
  • Marroni et al.’s (2026) do not acknowledge the difficulties in detecting pathogens on imported plants. See previous blogs describing continuing introductions of pathogens on plan imports by scrolling below “Comments” and “Archive” to “Categories” and click on “forest health” or “plants as vectors”. Perhaps the New Zealand procedures are sufficiently robust to overcome weaknesses detected in the U.S. and elsewhere … but that is not clear.
  • New Zealand scientist do not know how the oomycete Phytophthora agathidicida which kills the endemic kauri tree, Agathis australis was introduced. Does this situation conceal some other pathway?
a kauri tree; photo by F.T. Campbell

Uncertainties acknowledged by Marroni et al. (2026)

  • Hawai`i adopting regulations in 2016 to prohibit movement of M. polymorpha plant material from infected regions; this was six years after the disease was first detected. The disease was detected on Kaua‘i in 2018 and 2019, later on Maui and O‘ahu. Do these outbreaks demonstrate the limits of regulation? Or were these outbreaks initiated before the regulation was implemented—given the frequent lag in detection?
  • Asymptomatic infections have been detected on M. excels. Might other species also harbor undetected disease?
  • Scientists don’t know which species of Metrosideros trees, ambrosia beetles, or Ceratocystis fungi are established on which Pacific islands? Their presence or absence is relevant to the possibility of step-by-step spread of the pathogens.
  • Scientists don’t know how the pathogen might respond to seasonal temperature variations on New Zealand.
  • There is very little information on whether tissue culture plantlets can transmit Ceratocystis spp.
  • New Zealand has 12 native and 12 introduced species of Scolytinae, including Xyl. saxesenii [which has transmitted C. lukuohia and C. huliohia under lab conditions]; and Amasa truncata, an Australian ambrosia beetle species implicated in mortality of trees. There is little data regarding which insects associate with Metrosideros.

  • Proposed solutions

Marroni et al. (2026) say New Zealand’s recent sobering experience with myrtle rust https://www.dontmovefirewood.org/pest_pathogen/ohia-rust-html/ demonstrates the importance of quick action if a pathogen is introduced. Suggested priorities are to strengthen pathway management, improve surveillance in climatically suitable regions and at high-risk entry points, and research to address major knowledge gaps relating to host range, climate suitability, potential vectors, and dispersal. Scientists should test a broader range of possible hosts, including representative native forest species and economically important fruit and commercial forestry crops. Other studies are needed to determine which ambrosia beetle species utilize Metrosideros trees.

Pathologists should clarify which Ceratocystis species are already present in New Zealand and the South Pacific. Currently, only Ceratocystis fimbriata sensu stricto is recognized as occurring in New Zealand. However, New Zealand shares many fungi from other taxonomic groups with native forests in Asia and Australia, so Marroni et al. (2026) expect that some Ceratocystis species in the Austroasian clade might also occur naturally in New Zealand without causing obvious disease symptoms. Research is also needed to illuminate the influence of seasonality and local microclimates on disease outbreaks. A better understanding of these variables will inform long-term biosecurity and forest health planning.

Marroni et al. (2026) note that protecting Aotearoa New Zealand forests and primary industries requires collaboration of researchers, biosecurity agencies, Māori and Pacific local communities, and policymakers. They advocate a multidisciplinary approach that considers biological, cultural, and social factors.

Palau islands; photo by Luka Peternal via Wikimedia

Tree Mortality on Palau

Fear of spread of tree-killing Ceratocystis species across Pacific Island groups is not theoretical. In late 2021 people noticed extensive mortality of mature udeuid (Manilkara udoido) trees in Palau, an independent country in the Micronesian Islands east of the Philippines – so in the North Pacific. Udeuid is a culturally and ecologically important forest tree endemic to just one of the Palauan islands, the largest, Babeldaob Island (Johnson et al. 2025).

Losses exceeded 50% in several areas within the species’ core range. Koch’s Postulates determined the causal agent to be Ceratocystis manginecans, a Brazilian species associated with major disease outbreaks in Asia and elsewhere. Extensive damage to large udeuid trees caused by Typhoon Surigae in April 2021 might have contributed to the outbreak by creating wounds for infection. Four years after the initial detection trees continue to die. This is the first report of C. manginecans on the genus Manilkara andits first detection in the Pacific Islands. Johnson et al. (2025) conclude that C. manginecans poses a serious threat to native forests and cultivated crops in Oceania.

SOURCES

Johnson,J.A., M.A. Hughes,P.I. Bennett,O. Sadang,  K. Roy,  D.R. Kroese,  P.G. Cannon,  N.B. Klopfenstein,T. C. Harrington, and Mee-Sook Kim. 2025. First Report of Ceratocystis manginecans Causing Udeuid (Manilkara udoido) Wilt in Palau Plant Disease December 2025  https://doi.org/10.1094/PDIS-07-25- 1554-PDN 2025

Marroni, M.V., M.R. McNeill, R.E. Campbell, P.R. Johnston, T. Waiariki, A. Puketapu, W. Awarau‑Morris, J. L. Hasna, B. S. Beresford, J. Tyson, B. Weir, G.R. Smith, M. Padamsee, J.K. McCarthy, T.R. Etherington, B. Ganley, B.C. Luiz, L.M. Keith. 2026. The risk of rapid ‘ōhi‘a death to Aotearoa New Zealand and South Pacific. Biol Invasions (2026) 28:207 https://doi.org/10.1007/s10530-026-03896-2

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

Or

https://fadingforests.org

Rapid growth of a coalition tackling invasive plants in Virginia!

The Virginia Invasive Plants Coalition was formed at December 2023. Seventy-six organizations participated in the formative meeting. The Coalition now boasts 113 members. CISP joined the coalition this autumn.

The Coalition’s purpose of is to identify and carry forward statewide efforts to make dramatic progress against invasive plants support the use of native plants. Members work collectively on ten initiatives:

  • awareness & education;
  • resource development;
  • support & implement a Virginia Invasive Species Management Plan;
  • create or provide expertise, incentives, and access to funds to help private land stewards mitigate invasive species
  • limit access to invasive plant;
  • research to identify & address knowledge gaps;
  • remove invasive plants & restore with native plants;
  • ensure equitable access;
  • build collaborative networks;
  • ensure that Virginia adopts policies that support reduction of invasive plants & reverse the damage they cause

I rejoice that the Coalition explicitly includes advocacy for state-level policy. I wonder whether – over time – VIPC members might consider advocating for more effective federal policies.

I also wonder whether organizations concerned about invasive species have formed similar broad and action-oriented coalitions in other states.

I will focus here on two VIPC efforts.

Virginia State Capitol; photo by Tony Fischer via Flickr
  1. Policy

Virginia currently has two lists of invasive plants. The Department of Agriculture and Consumer Services (VDACS) lists “noxious weeds”. It currently contains 26 species in three tiers. It is illegal to sell species on this list. The Department of Conservation and Recreation (DCR) maintains the Virginia invasive plant list. The list contains 103 species. It includes a list of species identified to spur “early detection”. All noxious weeds are also included on the “invasive” list, but not all “invasive” plants are listed as noxious weeds.

burning bush – on the DCR invasive plant list but not the VDACS noxious weed list; photo by F.T. Campbell in Fairfax County, Virginia

VIPC is a member of the Virginia Conservation Network. This coalition has developed a conservation agenda for 2027; the agenda has four categories: water; land & wildlife conservation; climate & energy; land use & transportation. “Preventing harm from invasive plants” is included under the “Native habitats & species” chapter.

In 2026 the state legislature adopted four laws that:

a) added invasive plant management to the powers of service districts; [A “service district” is a defined geographic area within a local government established to provide additional, more complete, or more timely governmental services than those generally provided to the rest of the locality];

b) removed the “commercial viability” loophole from the state’s noxious weeds law;

c) required Virginia’s Department of Transportation to create a plan for managing invasive plants along  public roadways; &

d) allowed volunteers to use herbicides on state-owned public lands when under supervision of a licensed commercial pesticide applicator.

Legislation also now requires retail outlets to place warning signs near each invasive plant species offered for sale (effective January 2027); partially funds the Virginia Invasive Species Management Plan; prohibits state agencies from planting, selling, or propagating invasive plants; requires tradespersons to provide written notification to property owners for all plants proposed for installation that are included on the list of invasive plants; & allows localities to permit the supervised use of herbicides by volunteers on public lands.

The Virginia Conservation Network considers these actions to be too limited. The VIPC asks its member organizations to advocate for

  • Require property sellers to disclose the presence of Japanese knotweed (Reynoutria / Fallopia japonica or Polygonum cuspidatum) on a property they are selling because it can disrupt underground infrastructure.
  • Tightening label language regarding whether a plant is “sterile”.
  • Require those clearing property for development to plant cover crops to forestall weed invasions if there is a delay in further work.
Japanese knotweed; photo by Will Parson, Chesapeake Bay Foundation

Perhaps in future the Network might broaden members’ concern about the loss of forest canopies to include insects and pathogens that kill trees?

2) Surveying nurseries to find those selling invasive plant species.

VIPC members carried out surveys in 2025 and again in 2026. The 2026 surveyors visited 122 nurseries in 60 locations across the Commonwealth. This was 42% more retailers than the 2025 survey. One-third of the nursery locations were in the Northern Virginia suburbs of Washington, D.C.

butterfly bush Buddleya davidii; photo from Free Public Images

The 2026 surveyors found a 23% decrease in invasive plant species being offered per retailer. Twelve percent of the garden centers had no invasive species for sale. This was more than triple the number found during 2025. However, one garden center was selling 24 of the 39 invasive plant species. The most commonly detected invasive species are:

  • butterfly bush — found during 95 visits; [see Douglas Tallamy on why butterfly larvae cannot use this plant.]
  • species found during 58 to 79 visits were nandina, English ivy, periwinkle, moneywort, and Japanese barberry;
  • Japanese spirea and burning bush were found during 45 or 44 visits;
  • Two ornamental grasses, Chinese silvergrass and fountain grass, were found during 30 or 29 visits;
  • species found during 19 to 16 visits were greater periwinkle, leatherleaf mahonia, Chinese privet, and winter creeper;
  • species found during eleven to eight visits were Chinese wisteria, mimosa, water hyacinth, yellow flag, sweet autumn clematis, and border privet;
  • species found during five or four visits were creeping Charlie, Callery pear, golden bamboo, and Norway maple.

Invasive species found at a smaller percentage of Virginia garden centers in 2026 than in 2025 were butterfly bush, nandina, English ivy, periwinkle, greater periwinkle, Chinese privet, winter creeper, sweet autumn clematis, border privet, Callery pear, and linden arrowwood.

Invasive species found at a higher percentage of retailers in 2026 than in 2025 were moneywort, Japanese spirea, Chinese silvergrass, mimosa, water hyacinth, yellow flag, and Japanese honeysuckle (Lonicera japonica). The last species is on the Virginia Noxious Weeds List, so sale is illegal.

Invasive species found at the same percentage of Virginia garden centers in 2026 as in 2025 were Japanese barberry, burning bush, fountain grass, leatherleaf mahonia, Chinese wisteria, creeping Charlie, golden bamboo, Norway maple, five-leaf akebia, parrotfeather beefsteak plant, Italian arum, white mulberry, Chinese tallow-tree, and trifoliate orange.

Invasive species not found offered for sale by surveyed garden centers in 2026 were Amur honeysuckle*, Autumn olive*, Brazilian waterweed, cinnamon vine, cogon grass*, crown-vetch, incised fumewort*, marsh dewflower, Morrow’s honeysuckle, Oriental bittersweet*, porcelain-berry*, purple loosestrife, ravenna grass, royal paulownia, shrubby bushclover*, Siberian elm, tartarian honeysuckle, thorny olive, tree-of-heaven*, wineberry, and winter honeysuckle. (*indicates plants listed on the Virginia Noxious Weeds List.)

oriental bittersweet; on Virginia’s noxious weed list (tier 3); Picture This

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

Or

https://fadingforests.org

Invasive species’ spread facilitated by inconsistent approaches

feral hogs — one the invasive species on which state approaches vary; photo by Creg Oneal via Flickr

Several groups of scientists are addressing systemic problems that impede efforts to counter bioinvasions. One of those problems is the lack of a consistent approach in federal systems. 

Drake et al. (2026) (full citation at the end of this blog) evaluate the impacts of this situation in the United States where – they argue – the national government has been slow to adopt overarching policies and provide adequate and dependable funds to implement them. The result is a patchwork of varying – even clashing – regulations and differing levels of effort that undermine program efficacy. Conflicting approaches add to such well-known challenges as limited budgets and evolving goals. They recommend applying such existing frameworks as the National Invasive Species Council’s (NISC) Early Detection / Rapid Response framework or One Biosecurity to facilitate integration and cooperation among the large variety of sectors affected. (NISC’s purpose is to coordinate federal agencies’ programs. The Council has no official role vis a vis state programs. Still, there is no legal impediment to states adopting any NISC approach which they consider appropriate.) At the same time Drake et al. (2026) warn against imposing too great uniformity or lacking flexibility.

I regret that Drake et al. (2026) do not mention the National Plant Board. The NPB focuses on managing plant pests (insects, pathogens, etc.) and invasive plants. The NPB recently celebrated its centennial anniversary. States have created fora under the NPB in which they exchange experiences with the goal of coordinating their efforts.

With respect to animal invaders (other than plant pests) or disease or parasite threats to animals, I believe there is no equivalent to the NPB. The Association of State Wildlife Agencies (AFWA) has an invasive species committee which discusses issues of general concern (see agenda from one of its meetings here).  This effort is much more recent than the NPB. It is similar in that it is consultative, with no authority to enforce a common approach.

Findings

Drake et al. (2026) explore the extent to which American states apply similar vs. different approaches to managing invasive species as a group and plants, invertebrates, and vertebrates separately. Lack of data forced them to exclude fungi and other microorganisms. They focused on 21 contiguous states in the eastern part of the country. They also compared the states’ lists of regulated species to national lists of invasive species compiled by the United States’ Register of Invasive and Introduced Species (US-RIIS) (Simpson et al., 2022; Simpson and Eyler, 2018) and U.S. Geological Survey Non-indigenous Aquatic Species database (NAS; U.S. Geological Survey, 2023).

A literature search revealed 1,117 state statutes, regulations, and similar policy documents that pertain to invasive species. One third of these documents (n = 448) named at least one taxon at the genus or species level. Of these, 35.3% named one or more plant species; 19.9% named one or more invertebrate; and 44.8% named vertebrates. Overall, 60.5% of these species were listed by only one state. Viewed by taxonomic group, this broke down to 40.6% of plant species, 60.6% of invertebrates, and 56.4% of vertebrates. Only four species are regulated in all 21 states = western (European) honeybee (Apis mellifera); and three agricultural weeds, creeping thistle (Cirsium arvense), quackgrass (Elymus repens), and dodder (Cuscuta species).

Cirsium arvense; photo by USchmidt via WikiMedia

Drake et al. (2026) found neighboring states did not share similar species lists or approaches. Consistency was even less at the regional scale, particularly when managing invasive invertebrates or vertebrates. The absence of a unified approach means that proactive states are susceptible to invasion from neighboring states which take a less vigorous stance. Since managing invasive species becomes more difficult and costly as the invasion progresses, undermining proactive policies undercuts efficiency.

Even when the national government does act, it lacks a unified approach. No federal legislation mandates a central authority to direct and implement IAS detection and response. The National Invasive Species Council (NISC), established by Executive Order 13112 in 1999, is supposed to provide high-level leadership to help overcome barriers to communication and promote collaboration among the several federal agencies bearing responsibility for various aspects of the issue. Authors, e.g., Reaser, Simpson, et al. (2020); Simberloff et al. (2020), say NISC’s effectiveness has been undermined by inconsistent funding and vacillating political support from policy-level leaders.

Drake et al. (2026) also assessed which of the 21 states took action proactively. Two plant species were listed by name by all 21 states: quackgrass (Elymus repens) and creeping thistle (Cirsium arvense). They called three states (14.3%) “pro-active” because they regulated quackgrass before it was detected in the state. Four states (19%) did the same regarding creeping thistle. The one invertebrate species listed by all 21 states, the western (European) honeybee, was established in these states before they began addressing invasive species, so it is not a test of states’ forethought.  

Of course, the policy goals differ between the two plant species and the honeybee: the former are considered damaging so policies focus on their control and management, whereas the honeybee is valued for pollination and honey production so policies aim at protecting it. There is no federal legislation regulating Apis mellifera individuals already in the country. State regulations governing interstate movement are the usual jumble of approaches. Drake et al. (2026) says this lack of consistency can increase the risk that introduced pathogens, pests, and undesirable subspecies (i.e., “Africanized” bees) will spread. They note that this chaos reigns despite bees’ importance to the agricultural sector.

Florida had policies governing the most species (345), Vermont the least (67). More surprising to me, New York regulated the most plant species (161); Mississippi the most invertebrates (105), and Virginia the most vertebrates (189).

Collectively the states regulate three times more species than appear on either national registry: 1,862 species in the state database versus 630 in US-RIIS or NAS databases. The states regulated a proportionally larger number of plant species and much smaller proportion of vertebrates. The number of species named in both state and federal databases were 360 plant species (57.1%), 170 invertebrates (28.4%), and 91 vertebrates (14.4%). The difference between federal and state lists is further magnified by the fact that significant numbers of species listed on the federal databases are managed by only one state: 143 plant species (48.3%), 86 invertebrates (29.1%), and 28 vertebrates (9.5%). In other words, only 217 plant species, 84 invertebrate species, and 63 of vertebrate species designated as invasive by federal databases were being managed by more than one state.

Carex extensa – one of plant species listed as invasive by USGS but not regulated by any of the 21 states; photo by botanygirl via Picture This

The survey identified a wide range of state agencies that have at least some responsibility for managing invasive species. These agencies’ principal concerns are agricultural, plant, or livestock industries; wildlife, fisheries, and recreation; forestry, mining, and natural resources; marine resources; public and environmental health; transportation, utilities, and commerce; and administration, education, specific locations, and all other types. Agriculture agencies are overwhelmingly responsible for invasive plants, insects, and arthropods; and almost equal to Fish and Wildlife departments in the case of managing molluscs. F&W departments are most often responsible for mammals, fish, crustaceans, amphibians and reptiles. Public and environmental health agencies are a distant second as regards responsibility for plants and arthropods, and third re: insects. Administration/education/specific location agencies are third most frequently given responsibility for plants; they hardly appear for other categories. Transport and commerce ranked fourth (nearly the same as public health agencies) for managing insects.

More than half of state policy measures (55.4%) related to terrestrial species, habitats, and pathways; 17.1% related to aquatic species, habitat, and introduction pathways; and 27.5% related to both.

Considering all species named in each state’s policy codes, about half of the listed taxa in each focal state’s policies are also listed by at least one neighboring state. At the regional level, overlapping or consistent policies declined to about 19% of the species. It doesn’t surprise me that New England states rank high in cooperation. Nor that the least number of species also regulated by neighboring states applies to Florida; the “sunshine state” is semitropical and has many types of ecosystems probably not present in Alabama or Georgia.

Once again, consistency is higher for plant species than the animal taxa. Among-neighbor overlap for plant taxa is ~69-70%, for invertebrates is ~50%, and for vertebrates only about a third. At the regional level, overlap is ~28% for plant species, ~18% for invertebrates, and 14% or less for vertebrates.

Drake et al. (2026) present case studies on several species to illustrate the breadth and depth of policy inconsistency, coordination, and implementation. The species studied are three of the four species regulated by all 21 states in the database; and three others selected to be emblematic of plant, invertebrate, and vertebrate taxonomic groups. The representative species for invertebrates is the emerald ash borer (EAB; Agrilus planipennis); the illustrative species for vertebrates is feral pigs (Sus scrofa). 

Drake et al. (2026) report that the EAB had been detected in all but two of the 21 states in their study – Florida and Mississippi (EAB has now been detected in the state). There was a federal quarantine until early 2021. Still, only 10 states (47.6%) have a policy regulating EAB per se. Nine states had acted proactively; this was the highest proportion among all the species analyzed, probably because the beetle spread so quickly and had such obvious and severe impacts observed.) My analysis of data on the Don’t Move Firewood website determined that few of these states regulate firewood. Seven states require treatment of firewood originating out-of-state. New York also prohibits movement of firewood within the state over distances exceeding 50 miles. Two states regulate firewood originating in location quarantined for a specific pest, e.g., EAB. Three states restrict movement of outside firewood onto state properties. The rest of the states urge people to “burn it where they buy it” but impose no requirements. In some cases, National parks for forests have more stringent regulations. I am quite disappointed how few states have taken protective actions. Drake et al. (2026) explained the absence of regulations in the other 11 states as possibly due to the slow pace of legislative action compared to the speed of spread. I think this factor deserves greater attention.

Drake et al. (2026) noted that there are cooperative programs that cross jurisdictional boundaries; these increase programs’ effectiveness. The example they cite is the Ash Protection Collaboration Across Wabanakik — a cooperative effort among federal, state, and tribal governments and non-governmental organizations in northern New England and bordering Canadian and tribal lands.

The discussion of feral pigs reported that these animals are becoming increasingly troublesome. The highest density of pig populations is in southern states but suitable habitat is found across North America. Twelve states have adopted relevant policies; five were proactive in doing so. Feral hogs are present in at least three of the nine states that lack any policy; they are also present in neighboring states of most. Drake et al. (2026) say that the patchwork of policies and regulatory agencies across (and even within states) has hindered management. One of the issues with feral hog management is the presence of conflicting views and stakeholders. Some states encourage hunting, others outlaw it in hopes of reducing any motivation to transport hogs to new areas to initiate sport hunting. They conclude that prohibiting private landowners from profiting from feral pig hunting opportunities, while apparently useful for control, might not be reasonable.

Drake et al. (2026) notes that there is no national policy but the federal government does provide financial assistance. Congressional legislation created the Feral Swine Eradication and Control Pilot Program (FSCP), co-managed by USDA Natural Resources Conservation Service and APHIS. They say that while federal and state investment is likely necessary to conduct the large-scale control needed, the public wants the opposite: they say those responsible for pig releases and individual landowners should pay for control efforts. Drake et al. (2026) discuss the situation in North Carolina to illustrate the conflicting approaches within one state.

Drake et al. (2026) find the greatest consistency across states in the regulation of invasive plants. This might reflect the historical attention to agricultural weeds. However, there are still inconsistencies that might cause confusion and facilitate unintended spread of invasive plants by the horticultural trade. (See my earlier blog here.) They point out that the lack of attention to invertebrates and vertebrates falls short considering the risks and costs these invaders impose at the national and global levels. In the eastern United State, five of the six costliest invasive species are invertebrates; the sixth is feral hogs.

Drake et al. (2026) worry that the widespread differences in approach leads to inaccurate estimates of invasive species’ economic cost as well as reduces states’ ability to effectively plan and coordinate efforts. They concede that given the range of agencies and industries that contribute to invasive species management, their review of state policies might not accurately reflect the full effort. Also the engagement of multiple players enhances flexibility. However, the disconnect between policy and on-the-ground actions can be a barrier to effective communication and compliance. It might also result in duplication and missed opportunities for collaborative management on common goals in neighboring states.

Drake et al. (2026) concede that social acceptance affects implementation. The most cost-effective, efficient, and impactful control methods might be socially unacceptable. Often social acceptance comes after an invasive species has spread and established – so after counter action is most successful and cost-effective.

Drake et al. (2026) note that climate change is likely to reduce barriers to invasive species’ spread and establishment and facilitate transition of benign non-indigenous species into damaging invaders. They say there is an urgent need for more attention from policymakers to the threat posed to both the economy and ecological systems. Their example is the contrast between the concentration of forest insect pests in the northeast while Florida and Mississippi list the highest number of species. Drake et al. (2026) suggest these listings reflect the region’s forestry sector’s concern about non-native pests – but I have not seen such interest (See profile of Sirex woodwasp here.)

To reduce vacillations in federal policy when administrations change, Drake et al. (2026) urge Congress to adopt strong, overarching legislation. If that isn’t possible, they say the second best option is to strengthen incentives and procedures for interstate cooperation. Such an approach could be extended to Canadian provinces

Drake et al. (2026) say it is clear from their own and others’ work that current policy tools fall short and leave proactive states at risk of threats from their neighbors. A possible model is competitive and non-competitive State Wildlife Grants program managed by the U.S. Fish and Wildlife Service. These funds should complement, not be reallocated from, current conservation efforts.

They praise some efforts by NISC, specifically the Early Detection Rapid Response framework, as a way to spur improved communication among policymakers, practitioners, and researchers. However, given the many remaining legislative and regulatory gaps, and differing interpretations, they suggest increasing opportunities of practitioners to use existing research and outreach structures e.g., Land Grant institution extension model. New frameworks such as translational invasion ecology can improve identification of research priorities and transfer of generated knowledge. These frameworks explicitly take into account the ecological, sociological, economic, and political contexts. Incorporating diverse stakeholders and quantitative tools e.g., through simulations, climate change projections, connectivity assessments, and species distribution maps that take into account the socio-economic components might be able to more holistically evaluate and act upon the potential threats.

Drake et al. (2026) call for increased attention to researching species likely to become problematic in the future. They note that only four of 18 NIS species in New England identified by another’s study as likely to benefit from climate change are included under policies of at least one state in the region.

SOURCE

Drake, J., E.M.X. Reed, D. Haak, B. Brown, M.C. Mims, M.G. Sorice, H. Rogers, S. Salom, T. Schenk, and J.N. Barney. 2026. State Lines and Species Divides: Inconsistencies and Opportunities in Invasive Species Policies across the eastern United States. Ecological Applications 36(5): e70287. https://doi.org/10.1002/eap.70287

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

Or

https://fadingforests.org

If you care about invasive species, keep the USFS’ Roadless Rule. Read why here

Copper-Salmon Wilderness in Rogue River Siskiyou NF; one of last low-elevation habitat for healthy Port-Orford cedar; photo from USFS

CISP submitted official public comments to the USDA Forest Service opposing the proposed recission of the Roadless Area Conservation Rule, aka ,the roadless rule. Our opposition is based on the heightened risk of invasive species introductions associated with easier human access. Vice President Phyllis Windle wrote the comments.

The proposed recission is published here.

The roadless rule was adopted in 2001—available here. This regulation prohibits road construction, road reconstruction, and timber harvesting on approximately 44.7 million acres of National Forest System lands, including in Alaska. It is not in effect in Colorado or Idaho because those states have state-specific regulations.

According to the proposal, rescinding the 2001 Roadless Rule is intended to return decision-making for these activities to local officials, in conjunction with forest-level land management planning.

Rescission of the roadless rule would be one of the largest conservation policy changes in recent years.

As required by the National Environmental Policy Act (NEPA), the USFS prepared a draft environmental impact statement (DEIS) analysing the likely effects of allowing local forest managers to open currently road-free areas to construction of temporary or permanent roads. Our review focussed on the 300-plus  pages in Volume 1. Phyllis found that division of the analysis into multiple major and minor sections muddied the conclusions and failed to provide an accessible, integrated view.

(The DEIS included two additional volumes totaling 600-plus pages – almost all letters from tribes, congress, states, and localities). Supporting biological and economic documents added nearly 900 more pages. Mostly these were detailed analyses by the US Fish and Wildlife Service and the National Marine Fisheries Service.)  

Worse, the backlog in updating individual National forests’ management plans undercuts the ability of local managers to understand current conditions and adopt truly appropriate strategies. (As of March 2023, 99 management plans are older than the legal maximum of 15 years.) The DEIS also does not demonstrate how individual national forests can address problems that cross their own or state boundaries – threats that include those from invasive species.

Phyllis notes that evaluating the benefits and environmental downsides of constructing roads in specific National forest areas will require more complex plans than those developed in the past – and which are so badly tardy. The DEIS does not address how the current planning process can meet the demands of the new responsibilities associated with ending the roadless rule.

Most important, the DEIS barely addresses the risk of spread of non-native insects and plant disease pathogens. CISP asserts that these organisms pose the greatest threats to forest health from invasive species. Yet the DEIS says only that “the presence and severity of pest infestations are influenced by local conditions…” like climate and the biological attributes of pests. (DEIS, Vol.1, p. 78.) A far broader set of conditions influence infestations. Among them are proximity to nurseries selling contaminated stock or homeowners planting such stock; camping enthusiasts moving insect-infested firewood (sometimes in violation of state quarantines); and people transporting invasive species during fire operations, with construction equipment, or on boats. As has been well recognized for decades, economic factors, international regulations, and the popularity of certain pets all affect the “presence and severity of pest infestations.”   

As we point out, non-native insects and pathogens are extremely damaging. Yet the DEIS discussion of insects appears to be based almost entirely on responding to damage caused by the native mountain pine beetle (Dendroctonus poderosae). There is no discussion of existing impacts or threats from, for example, the emerald ash borer – in eastern forests or in Pacific coast states; or the balsam woolly adelgid on subalpine fir (Abies lasiocarpa) in the Rockies. New outbreaks of these insects can result from careless visitors taking insect-infested firewood to formerly inaccessible locations.

BWA-killed subalpine fir in Oregon in 1959; photo by Ken H. Wright USFS

Failure to mention major and potential plant pathogens is an even more glaring gap since they are often harder to identify, more difficult to detect, deadly … and their spread is sometimes quite intimately linked to roads. The link is best documented for Phytophthora species. The DEIS does not address the many examples already present in National forests. Port-Orford-Cedar root disease (Phytophthora lateralis) has killed up to 90% of its hosts at high-risk sites. It is well-documented as being spread by construction and use of roads (Betlejewski et al. 2011). Sudden oak death has killed an estimated 50 million trees in northern California and southwestern Oregon. Phytophthora cinnamomi is widespread in eastern oak-dominated forests, where it is probably reducing productivity. This root pathogen poses serious challenges to efforts to restore American chestnut trees across most of its current range (Gustafson et al. 2022).  Its spores spread from tree to tree in water and through soil. In California, Phytophthora species introduced to wildlands on herbaceous species planted during restoration projects have spread downhill (Swiecki and Bernhardt 2018).

sites of SOD infection in Oregon; map by Oregon Department of Forestry

In all these cases, roads, vehicles, fill dirt or gravel, even shoes can have spread the pathogen.  Swiecki and Bernhardt’s (2018) Best Management Practices could help prevent introduction and spread via trail work, construction, and imports of soil. It is not clear whether they have been adapted and implemented widely by land management agencies.

Phyllis suggests that the DEIS should have included a case study reviewing presence and impacts of Phytophthora species in American forests, with the focus on how the pathogens are being introduced and spread. The analysis should closely examine how the three alternatives in the DEIS would help or hinder control of these pathogens – for a specific invasive species, in specific places. She notes that actually preventing a pathogen’s introduction and spread differs from planning what to do. The proposal’s emphasis on planning seems risky.   

The DEIS allots more attention to the nexus between invasive plant species’ introduction and spread and road access. It is widely acknowledged that invasive plants can penetrate deep into forests and alter or eliminate biodiversity, scenic, and other forest values. One weakness in the DEIS is that it is not clear which invasive plant species are being mapped in USFS projects. Instead, the text says that “… invasive plants are ranked and identified as being invasive or noxious in the state in which they occur.” The DEIS does not acknowledge that state noxious weed lists are usually focused on agricultural weeds, not those that can invade intact forests. As we noted in an earlier blog, the list of plant species tracked by the Forest Inventory and Analysis (FIA) program does not include numerous such species, e.g., wavy-leaf basketgrass (Oplismenus undulatifolius), fig buttercup (Ficaria verna; formerly Ranunculus ficaria), shrub and creeping Euonymus, callery pear (Pyrus calleryana). Among shrubs, only one privet (Ligustrum vulgare) is included. Plus, since plant species’ status differs from state, shifting authority to Forest level decision-makers could sow confusion and conflict over jurisdictional differences.

wavy-leaf basketgrass invasion; photo by Kerry Kyde, Maryland DNR & Bugwood

The FIA data analysis I reported on in this blog noted both that plant invasions are much more intense in the wildland-urban interface (WUI) and that National forests across the Lower 48 are less invaded by non-native plants than forests under other ownerships. I concluded that the principal reason for increased integrity of forests under federal management is current management: protection from road-building and harvesting over many decades. Allowing construction of roads into currently roadless areas threatens to expand the degrading influence of semi-developed areas.

The risk is high: sites best suited to growing industrial timber are also prone to invasion by non-native plant species. The FIA surveys found that 76% of highly productive plots were invaded compared to 40% of low-productivity plots. It is unclear whether highly productive sites are inherently more invadable, or, instead, that such plots were converted to agriculture earlier, so exposed to human disturbance longer.

Forest Pests Not a Priority?

In CISP’s comments, Phyllis noted that on December 30th, 2025, Secretary of Agriculture Brooke L. Rollins announced four new priorities for research and development. The third was “Protecting the Integrity of American Agriculture from Invasive Species.” Our review of materials accompanying the proposed rule change found little evidence that forest pests are receiving such priority attention.   

SOURCES

Betlejewski, F., D.J. Goheen, P.A. Angwin, R.A. Sniezko. 2011 Port-Orford-Cedar Root Disease. Published by USDA Forest Service, Pacific Northwest Region (R6), Portland, Oregon. FS/R6/RO/FIDL#131-11/009

Gustafson, E.J., B.R. Miranda, T.J. Dreaden, C.C. Pinchot, D.F. Jacobs. 2022.  Beyond blight: Phytophthora root rot under climate change limits populations of reintroduced American chestnut

Ecosphere. 2022;13:e3917.

Swiecki, T.J. and E. Bernhardt. 2018. Best Management Practices for Preventing Phytophthora Introduction and Spread:  Trail Work, Construction, Soil Import. Contract:  Development of Phytophthora BMPs for Golden Gate National Parks Conservancy

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

Or

https://fadingforests.org

Ash in the East: Can the many seelings & saplings reach reproductive age?

EAB-caused mortality of ash in Midwest; photo by Nathan Siegert, USFS

The 20th anniversary of detection of the emerald ash borer (EAB; Agrilus planipennis) in southeast Michigan has prompted reviews of the current situation. Tayal and Perry (2026) analyzed data from invasion-spanning research sites to investigate the extent of ash regeneration. Mortality of black ash (Fraxinus nigra), green ash (Fraxinus pennsylvanica), and white ash (Fraxinus americana) had exceeded 99% in these forests, with a concurrent precipitous decline of viable seed production.

They found that regenerating ash are abundant in the understory of post-outbreak forests. Among the 638 understory trees in the survey, basal area was highest for ash, followed by elm (Ulmus species.), maple (Acer species.), and musclewood (Carpinus caroliniana). On upland (xeric) and riparian (mesic) sites, ash are primarily in seedling and sapling size classes. Larger ash are more plentiful in wetland forests; the seven canopy ash trees were all in wetland forests.

The emerald ash borer is present in low numbers in all study sites.

Many ash of susceptible size (≥2.5 cm dbh) have symptoms of EAB infestation. Several of these symptoms (e.g., woodpecker damage, presence of epicormic sprouts, and canopy decline) grow more established as the trees grow. Still, 57% trees ≥5 cm dbh have healthy canopies. D-shaped adult beetle exit holes were detected on only 2% of the ash.

black ash swamp in Minnesota; photo by Eli Sagor via Flickr

Tayal and Perry (2026) concluded that the black and green ash in wetland forests are able to respond quickly to the multi-tree gaps produced by EAB-induced death of their dominant predecessors in these systems. These gaps result in more light availability and growing space than the single-tree gaps created by mortality of individual ash in mixed-species riparian or upland systems.

Other tree species that also flourished in the aftermath forests were maples, esp silver maple (Acer saccharinum), have become dominant in the overstories of wetland forests in northern US and Canada. In late successional floodplain forest systems, the maples are joined by other species with a tolerance for cold, flooding, and shade including elm (e.g., Ulmus americana); tamarack (Larix laricina) and yellow birch (Betula alleghaniensis).

Of course, American elm is threatened by a separate invasive species, the pathogens Ophiostoma ulmi and O. novo-ulmi. 

Tayal and Perry (2026) state several times that the future survival of this “orphaned” cohort of seedlings and saplings too small to have been colonized by EAB during the initial outbreak is uncertain. As they grow to susceptible size will they be attacked and killed by a growing population of beetles? Or will the biocontrol agents – assisted by woodpeckers – be effective in keeping EAB populations sufficiently low to allow the immature ash to reach reproductive size? Tayal and Perry (2026) cite Duan et al. (2023) as reporting that there is some evidence that the biocontrol agents can suppress EAB densities in immature ash. [Three agents – Oobius agrili, Spathius galinae, and Tetrastichus planipennisi – are established – in low numbers – in the forest sites studied.] So while the extent to which BC agents have protected regenerating ash in these long-term plots is still unknown, they express the hope that the parasitoids might be most effective in aftermath forests after EAB populations have peaked and then declined.

SOURCE

Tayal, A. and K.I. Perry. 2026. Status of ash (Fraxinus species.) in mixed hardwood post-outbreak forests near the epicentre of the emerald ash borer invasion. Agricultural and Forest Entomology, 1–12. Available from: https://doi.org/10.1111/afe.70067

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

Or

https://fadingforests.org

EAB in Pacific Northwest: likely impacts (expanded)

the Oregon ash-dominated wetland in Arkany National Wildlife Refuge in Oregon’s Willamette Valley; photo by Wyatt Williams, Oregon Department of Forestry

Two years ago I posted a blog summarizing the probable impact of the emerald ash borer (EAB; Agrilus planipennis) in Oregon. Reminder: the EAB was detected in Forest Grove, Oregon (west of Portland) in 2022. Scientists determined that it had been present for four to six years at that time.

In her Master’s thesis, Chloe Hull (2024) confirms that nearly all forested wetlands in the state’s Willamette Valley are comprised overwhelmingly of Oregon ash (Fraxinus latifolia). Therefore, these wetlands are likely to undergo rapid, significant shifts in vegetation, hydrology, and soils — unraveling their ecosystem functions. Hull warns that no management approach can restore those wetlands to perform the full breadth of their pre-settlement function and diversity. She suggests instead strategies to maintain these areas as wetlands – even if different types.

Hull’s conclusions are based on the expectation that Oregon ash will be killed by EAB infestation at levels similar to black (Fraxinus nigra), white (F. americana), and green (F. pennsylvanica) ash in the Midwest, i.e., up to 99%.

What is Threatened?

Wetlands provide numerous benefits to both human and natural systems, including purification of surface waters, habitats for plant and animal species, and food sources. Hull cites studies estimating that natural wetlands deliver 43.5% of the total global monetary value of ecosystem services provided by all natural biomes despite making up only ~3% of the world’s surface area.

In the Lower 48 United States more than half of wetlands have been converted to other land use types since 1780. In Oregon statewide, the extent of loss is lower: 38%. However, in the Willamette Valley specifically, the estimated loss is 57%.

Hull describes the pre-settlement wetlands of the Willamette Valley and the forces that have transformed them.

The most widespread of these wetlands were wet prairies, covering about 137,277 ha. Wetland, or bottomland, forests occupied about 97,477 ha. These forests typically formed bands along river or stream channels; they were also found occasionally in beaver swamps. These forests were composed of fire-intolerant deciduous trees in various densities. Stands along active channels typically willows (Salix species.), red alder (Alnus rubra), white alder (Alnus rhombifolia), and black cottonwood (Populus trichocarpa). On slightly higher terraces, where the inundations were less frequent, grew Oregon ash, bigleaf maple (Acer macrophyllum), and Oregon white oak (Quercus garryana). Ash and oak were particularly important along many smaller stream channels surrounded by open prairies.

Kinkaid’s lupine; photo from “Picture This” website

The wet prairies provide habitat for two federally-listed endangered plant species [Willamette daisy (Erigeron decumbens var. decumbens) and Kincaid’s lupine (T. Lupinus sulphureus species. kincaidii)]; and four state-listed species [white rock larkspur (Delphinium leucophaeum), peacock larkspur (Delphinium pavonaceum), Willamette navarretia (Navarretia willamettensis) and white fairy poppy (Meconella oregana)].  Two plant species and a butterfly formerly listed by the U.S. Fish and Wildlife Service [golden paintbrush (Castilleja levisecta) and Bradshaw’s lomatium (Lomatium bradshawii), and the Nelson’s checkermallow (Sidalcea nelsoniana)] are also present.

Both types of wetlands were maintained in part by periodic burning by the resident Indigenous peoples. These actions promoted a habitat mosaic of tufted hairgrass (Deschampsia cespitosa) prairies, camas lily (Camassia quamash) wet prairies, Oregon white oak savannas, and ash-dominated bottomland riparian forests. The Willamette River meandered and formed braided channels, with resulting flooding and wetland habitats.

In 1855 the federal government forced the Indigenous peoples to leave the valley. Since then, the wetlands have been drained and converted into agricultural fields; or drowned by various flood-control dams, diversions, and levees. As a result, Hull says, the Willamette Valley has been largely disconnected from the river. In addition, Euro-Americans have introduced non-native plants and intensive livestock grazing. Overall, the valley has lost the wetlands’ ecosystem functions.

Current (pre-EAB-induced mortality) Context

In the absence of disturbance, ash tends to be most important early-seral and final climax tree species. It plays a crucial role in regulating and supporting other species, hydrology, carbon storage, nutrient cycling, and overall resource availability.

Oregon ash are medium-sized trees, growing up to 24 m (80 ft) high and a dbh of 75 cm (30 in). Ash are long-lived, probably up to 250 years. They are thought to reach sexual maturity at ~ 30 years.

Oregon ash are adapted to the clayey, soggy conditions of the valley. (The average clay component of Willamette soils is 60-70%. When they become saturated there is prolonged surface ponding.) They also occupy drier, well-drained sites. Ashes’ tolerance of other environmental conditions, e.g., flooding, drought, salinity, soil pH, etc., is unknown.

Hull based her conclusions on analysis of four ash-dominated wetlands in the central Willamette Valley. Although only ~ 24 km apart, the sites differ in vegetation community composition, hydrology, and past and current other management goals.   

Site number 1 (Jackson Frazier) comprises primarily wetlands; current management is attempting to restore the wet prairie system, with little attention to forested wetlands. The second site (Mulkey Creek) is managed primarily to maintain oak woodland and prairie habitat. The third site (Poultry Center) is a university research facility. The fourth site (Shedd) has both natural drainage (two sloughs and a creek) and a relatively intact bottomland forest. This property often hosts public off-roading events so owners maintain trails and camping areas.

Hull determined vegetation types and management activities on these sites since 1948 by examining aerial photographs.

At all sites ash trees grew larger and stands increased in density between 1948 and 1978. Averaged across all sites, Oregon ash comprise more than 92% of forest canopy composition. The species reached 100% in some plots at some of the four sites. The second most common species in the canopy is the native black hawthorn (Crataegus douglasii). Among the other species are several non-native fruit or flowering trees [crabapple (Malus species.), pear (Pyrus species.), plum (Prunus species.)], Oregon white oak, and other species. Overall ash density was highest in the Shedd site, decreasing through Poultry Center and Mulkey Creek to Jackson Frasier. Rankings were different when she considered the balance between adult and sapling ashes: Jackson Frasier has the highest proportion of ash seedlings (93% of total saplings at one plot; 75% at a second); Poultry Center ranked second (70% of all saplings across all study quadrants). There are very few ash saplings at Mulkey Creek and Shedd (the last has only 4 ash saplings on the entire study site). Hull attributes these very low numbers to competition between adult and sapling ash.

EAB damage along a Mid-Atlantic river; is this what will happen in Oregon? photo by Leslie A. Brice

Anticipated Impacts of Ash Mortality

Hull expects 99% mortality of ash trees across the Willamette Valley in eight to 15 years. This will cause complete restructuring of the forest canopy and subsequent changes in disturbance regimes, flora and fauna communities, and land use. Currently there is no feasible way to restore ash-dominated wetlands. She explored three alternative future states, one of which describes several possibilities for maintaining different wetland ecosystem types.

Noting experience in the East, Hull concludes that there is extremely limited potential for ash regeneration following EAB-induced mortality. In the East an “orphaned cohort” of ash trees too small to have been infested in the initial invasion, or which sprouted after that event, has persisted so far. But its long-term survival and maturity is uncertain because EAB remain. See non-PMW article Especially since Oregon ash does not reach reproductive age for 30 years), tree mortality is likely to exceed seedling recruitment in these stands.

Still, since ash seeds banks decline rapidly after adult trees die, the orphaned cohort remains the most realistic opportunity for ash regeneration. It is hoped native woodpecker species and introduced biocontrol agents can sufficiently suppress EAB populations to create an opportunity for the saplings to achieve maturity and reproduce. See non-PMW article

Restoration

A majority of the literature and information about EAB effects on ash wetlands is from the Midwest. Willamette wetlands differ in soil characteristics and biotic and abiotic ecosystem components. Unlike the moderate to deep organic histosols underlain by clay in the Midwest, Willamette soils are hydric, defined as “a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part”. As noted above, saturation of these soils often results in prolonged surface ponding. Another factor is that most of the precipitation in Oregon is rain, not the snow of the upper Midwest. 

Hull evaluates the probability of maintaining each of her four sites as a wetland. She also considers how to prevent domination of the site by either currently established or newly introduced invasive weed species.   

Research in the Midwest indicates that wetland vegetation – in that case especially black ash trees — has a large influence on water table levels throughout the growing season. Simulated ash mortality led to a significant reduction in evapotranspiration and drawdown rates and a long-term rise in the water table. This was expected to promote conversion to open (herb-dominated) or shrub-dominated marshes.

In the Willamette Valley there are two types of wetlands not dependent on tall-stature trees – which are likely to disappear.

restored wet prairie near Eugene; photo by Bureau of Land Management

Pre-settlement, Willamette Valley wetlands were primarily wet prairies. Even now similar wetlands exist; they support a wide diversity of perennial and annual forbs and graminoids. Their floral diversity is due partly to traditional burning, partly to fine-scale vertical structures (“pedestals”) three to 20 cm high that support grasses and forbs on higher portions, rushes, sedges, and annual forbs on the lower, more often inundated surfaces. 

The second type of non-forested wetland is Scrub-Shrub Wetland. These occupy an ecological niche between a wet prairie and a forested wetland. They are dominated by fire intolerant woody vegetation kept short in stature by environmental conditions. Hull reports that these are relatively stable systems. They were once commonly maintained by beavers; Hull does not speculate about possibly restoring those ecosystem engineers. She does consider them to be potentially a successional stage in transition toward a forested wetland system. Oregon white oaks are among full-stature trees that can grow in these wetlands – in shrubby form.

Is it possible to restore forested wetlands by planting tree species other than ash? The success of this approach is challenged by the high clay component of soils and high water tables. None of tree species commonly associated with Oregon ash (red alder, black cottonwood, and bigleaf maple) can tolerate the same high clay soils. The species that do grow in clay soils (black hawthorn, some willows) are small (typically less than 6 meters tall) so they cannot fill the same ecological functions and niches as ash. A few large-form trees might tolerate saturated clay soils and serve a more similar ecological role. Hull names Oregon white oak and Willamette Valley ponderosa pine (Pinus ponderosa var. willamettensis). But these species are less tolerant of inundation.

Oregon white oak; photo by born1945 via Flickr

I notice the importance of Oregon oak (Quercus garryana) – both in existing forest and scrub habitats and as a possible replacement for ash. I am concerned that Hull does not mention that Oregon oak is also threatened by a non-native insect, the Mediterranean oak borer (Xyleborus monographus). Given this species’ presence I doubt that Oregon oak is a viable species for restoration of wetlands. I hope other scientists are exploring strategies for minimizing MOB’s damage to this important species.

Hull also discusses some tree species from elsewhere that are reported to be under consideration for planting in Willamette Valley wetlands. Several of these also are vulnerable to established non-native insects or pathogens. These include:

  • California black oak (Quercus kelloggii) – vulnerable to both the sudden oak death pathogen (Phytophthora ramorum) and the goldspotted oak borer (Agrilus auroguttatus). The latter is not yet found in Oregon.
  • Oregon myrtle (Umbellularia californica) – a host that supports sporulation by the sudden oak death pathogen (Phytophthora ramorum). SOD is established and spreading in southwest Oregon, on the other side of the coastal mountain range from the Willamette Valley.
  • Fremont cottonwood (Populus fremontii) and boxelder (Acer negundo) — both are vulnerable to yet other non-native beetles, the Euwallacea-fungus complex known in California as “invasive shot hole borers”. The closest known population of the complex is in the San Francisco Bay area.

Hull notes that in the Midwest, scientists are considering several species as potential replacements for black ash, including American elm (Ulmus americana), swamp white oak (Quercus bicolor), red maple (Acer rubrum), eastern white-cedar (Thuja occidentalis), and common hackberry (Celtis occidentalis). In this case she mentions concern around the viability of American elm in the presence of “Dutch” elm disease. The disease is present on elms planted in Portland and possibly other cities in Oregon.

Hull notes that little research has been conducted on questions now considered important, such as the ecological functioning of forested wetlands – including those in the Willamette Valley – and vegetation responses to changing water tables. As she points out, during the time it will take to assess replacement trees ash will probably be extirpated.

The Threat from Invasive Plants

Hull reports the presence of several state-designated noxious weeds in the Willamette Valley that pose a threat to maintaining natural wetlands. The two most common and persistent weeds in the valley’s wetlands are Himalayan blackberry (Rubus armeniacus) and reed canary grass (Phalaris arundinacea). She names several other species, including lesser celandine (Ficaria verna/Ranunculus ficaria) and Japanese knotweed (Polygonum cuspidatum) (both are highly invasive Mid-Atlantic bottomlands); several trees and shrubs; and various grasses.  

Ficaria invasion in the Mid-Atlantic; photo by F.T. Campbell

Management Options

Considering management options, Hull thinks it unlikely that officials will decide to do nothing because forests of standing dead ash are dangerous. She believes the best option is to harvest 20% of ash stands in 0.04 ha gaps and promote woody shrub establishment. Shrubs can provide some shade to streams and continued evapotranspiration and offset large rises in water table levels. The large amounts of down woody debris in streams could increase stream complexity and habitat as well as mitigate channelization. Hull notes that the resulting scrub-shrub habitats were common pre-settlement.

Regarding her four study sites, Hull considers two (Mulkey Creek and Shedd) are likely to become scrub-shrub wetland communities. Opportunity to plant tree seedlings at Shedd will depend on the density of understory vegetation. A third site, Poultry Center could transition to either an emergent (herb-dominated wetland or a scrub-shrub community. The direction of changedepends on whether increased surface evaporation leads to less ponding; or reductions in evapotranspiration rates leads to more ponding. Poultry Center is a reasonable candidate for tree species substitution if the hydrologic shifts are favorable. The wettest site, Jackson Frazier, will probably become an emergent wetland community, with a higher water table. It offers limited opportunities to establish alternative tree species.

Management of wetlands is further constrained by multiple restrictions, including state and federal laws; funding limitations; and visitor perceptions.

SOURCE

Hull, C. 2024. A Valley Without Ash: Exploring Strategies for Forested Wetland Restoration Post Emerald Ash Borer Invasion in the Willamette Valley, Oregon. MS thesis submitted to Oregon State University for the degree of Master of Forestry in Forest Ecosystems and Society

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

Or

https://fadingforests.org

EAB detected in Washington State; Pacific Coast states taking action

A newsletter issued by the Oregon Department of Forestry reports lots of action in Oregon and Washington in response to the presence of emerald ash borer (EAB; Agrilus planipennis). (To subscribe to the newsletter, email Jim Gersbach at jim.gersbach@odf.oregon.gov)

Ash-dominated swamp in the Willamette Valley; photo by Wyatt Williams, Oregon Department of Forestry

In Oregon, where EAB was detected in 2022, cities are taking protective actions. In Portland EAB was officially detected inside city limits in late summer 2025 east of the I-205 freeway. So far the beetle has not been reported from elsewhere inside city limits. To better establish where EAB is present, officials plan to girdle 4 ash trees in spring 2027 in hopes that female EAB will be attracted to them and oviposit. Those trees will be cut down in the fall, then examined to determine if any larvae are inside. This method has been used to help pinpoint where EAB is spreading before obvious signs of tree dieback are apparent. Oregon Department of Forestry will demonstrate the techniques for staff from the City of Portland, Oregon Dept. of Agriculture, U.S. Forest Service, Washington Dept. of Natural Resources, and Clackamas Soil & Water Conservation District.

EAB was confirmed within the city limits of Beaverton during summer 2026. The Beaverton City Council has adopted legislation expanding pesticide protection to1,400 ash street treesabove the 600 already treated in 2025. Treatment – injection of emamectin benzoate – is scheduled to begin in spring 2027 and be completed by September 2027. Last year city workers also protected 22 significant native Oregon ash trees (Fraxinus latifolia) over 20” dbh in a city-maintained natural grove that is predominantly ash.

EAB was detected in Silverton by a local tree care professional in summer 2026. The nearby Oregon Garden responded by treating eight ash trees on its grounds – all exotic to the region (seven white ash [eastern North America] & one narrow-leaved ash [Europe]). The Garden receives ~100,000 visitors a year.  The treatments were supervised by Oregon Dept. of Forestry & Oregon Forestry Resource Institute staff.

In Washington State, where EAB was detected in August 2026, near Vancouver, the state has regulated firewood imported from sources outside the state. The quarantine on untreated firewood from outside the state was adopted in February by the state Legislature. It took effect on August 18.  The rule prohibits importation into WA of untreated firewood from outside the state. Firewood imported into WA must be heat-treated to a minimum woodcore temperature of 160o F (71o C) for at least 60 minutes or receive an equivalent WSDA-approved treatment. The wood must also be labeled to show its source & display the statement “Approved Pest Free”. Firewood harvested within Washington State is exempt as are processed wood products, such as compressed wood bricks, wood pellets, logs, or wood products transported for industrial uses, such as to sawmills, pulp & paper mills, & biomass or wood composite facilities. Civil penalties up to $5,000 per violation can be imposed.

The newsletter provides updates on Europe’s double threat: EAB & ash dieback pathogen. 

Europe is home to three species of ash: common ash (Fraxinus excelsior), manna ash (F. ornus), & narrow-leaved ash (F. angustifolia). 

Hungary is the first European Union country with a confirmed EAB infestation (summer 2026). Neighboring Slovakia has also reported EAB presence but this is still unconfirmed.  

While the EAB is native to the Russian Far East & other parts of East Asia, it was not seen west of the Ural Mountains before 2007, when it was reported in western Russia. By 2019 the pest had been recorded in Ukraine & Belarus. Researchers at Ohio State University have found that F. excelsior has at least moderate resistance to EAB.

Fraxinus excelsior in Belgium; photo by Jean-Pol Gramont

The ash decline pathogen (Hymenoscyphus fraxineus) is also from East Asia. It was first described in Poland in 1992 [although probably present much earlier, perhaps the 1990s (Tolio et al., 2025)]. It is now widespread in Europe. Where present, it has killed the vast majority of ash trees. To ascertain whether Oregon ash (Fraxinus latifolia) might be attacked, USDA Forest Geneticist Richard Sniezko of the Dorena Genetic Resource Center has sent seed to European colleagues so that they can plant them and track the results.   

Some good news: British scientists report ~5% of F. excelsior trees appear to exhibit resistance to the parthogen and in some ash groves in northern England ~90% of young seedlings appear to be resistant.

The USDA Forest Service will hold a webinar on Oct. 6th to discuss EAB resistance ash breeding 

Mary Mason, a geneticist w/ USFS Northern Research Station, will present. The webinar starts at 1 PM Eastern Daylight Time on Tuesday, Oct. 6.

Publications named by the Oregon newsletter that are particularly related to the situation in Oregon):

• Hull, C. 2024. A Valley Without Ash: Exploring Strategies for Forested Wetland Restoration Post Emerald Ash Borer Invasion in the Willamette Valley, Oregon. Oregon State University. https://ir.library.ORstate.edu/concern/graduate_projects/3j333b36w

• Melton, A.E., Faske, T.M., Sniezko, R.A., Thibault, T., Williams, W., Parchman, T. & Hamilton, J.A. 2025. Genomics-Driven Monitoring of Fraxinus latifolia (Oregon Ash) to Inform Conservation & emerald ash borer Resistance Breeding. Molecular Ecology e17640. https://doi.org/10.1111/mec.17640  

 • Monitoring Oregon ash forests in the face of the emerald ash borer: A guide for small woodland owners & managers https://extension.ORstate.edu/catalog/pub/em-9451-monitoring-OR-ash-forests-face-emerald-ashborer

• Larval development & parasitism of emerald ash borer (Agrilus planipennis) in Oregon ash (Fraxinus latifolia) & European olive (Olea europaea): implications for the West Coast invasion Journal of Economic Entomology | Oxford Academic

• Maze, D., Bond, J. & Mattsson, M. 2024. Modelling impacts to water quality in salmonid-bearing waterways following the introduction of emerald ash borer in the Pacific Northwest, USA. Biol Invasions (2024). https://doi.org/10.1007/s10530-024-03340-3  

• Kral, G. & D.C. Shaw. 2023. Alternatives to Ash in Western Oregon: With a Critical Tree Under Threat, These Options Can Help Fill Habitat Niche. Oregon State University Extension EM 9396. https://catalog.extension.ORstate.edu/em9396

• Oregon Ash: Insects, Pathogens & Tree Health by Oregon State University Extension (also available in Spanish)  https://extension.ORstate.edu/pub/em-9380  

Useful links for more information

Map to find where EAB is currently confirmed in Oregon: https://experience.arcgis.com/experience/9f29b1860cb04d36ad71b122148277f3

EAB monitoring guidance https://www.OR.gov/odf/forestbenefits/Documents/eab-monitoring-guidance.pdf

Oregon Department of Agriculture https://www.oda.direct/EAB  

Oregon Department of Forestry  https://www.OR.gov/odf/forestbenefits/pages/foresthealth.aspx  

Oregon State University Extension https://extension.ORstate.edu/collection/emerald-ash-borer-resources  

Emerald Ash Borer Information Network, a collaborative effort by the USDA Forest Service & Michigan State University www.emeraldashborer.info  

SOURCE

Tolio, B., P. Sherwood, D. Marčiulynienė, C. Crocoll, M. Cleary, M. Liziniewicz. 2026. Constitutive Metabolite Profiling of European & Asian Fraxinus with Varying Susceptibility to Ash Dieback. Journal of Chemical Ecology 52:8 https://doi.org/10.1007/s10886-025-01678-z

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

Or

https://fadingforests.org

Wood Packaging: additional information re: continuing introductions

LEAD Technologies Inc. V1.01

Twenty-four years ago the international community adopted ISPM#15 with the aim of reducing forest pest introductions via the wood used to make crates, pallets, and other forms of wood packaging (SWPM). Over that period questions have been raised about its efficacy. See the analyses by Haack et al. I have posted numerous blogs about wood packaging introductions, focused on the United States. To review these, on this website, scroll below the “Archives” to “Categories”, click on “wood packaging”.

Scientists continue to analyze data on wood borer introductions to explore patterns and evaluate the standard’s efficacy. Two recent articles focus on woodwasps in the Siricidae (Nardi et al. 2026) and ambrosia beetles in the Euwallacea complex (Lanschler et al. 2026). Full citations for both are at the end of this blog.

Sirex woodwasps

S. noctilio in Argentina; photo by Paula or Vicki Klasmer via Bugwood

A group of scientist led by D. Nardi surveyed woodwasp introductions to the United States, Canada, and New Zealand to determine historic and current patterns. They found that:

1) Nearly all Sirex woodwasps (84.2% – 97.6%) are transported in wood packaging.

2) While most introductions originated in the woodwasps’ native regions of Europe and Eastern Asia, accompanying high volumes of commodities imported from those regions, interceptions from the Southern Hemisphere have increased recently. Nardi et al. speculate that Asian countries might use softwoods (conifer species) less often for SWPM than do Europe and North America. Certainly the most infamous invasive wood borers from Asia are those that attack hardwoods, e.g., Asian longhorned beetle, emerald ash borer, invasive shothole borers.

3) Widespread adoption of ISPM#15 has significantly reduced interception, establishment, and damage associated with Siricids in the U.S., Canada, and New Zealand since 2002. However, continued detection of live Siricids in wood packaging demonstrates the need for strict enforcement of the standard’s provisions and potentially adoption of additional mitigation strategies.

4) Data collected by phytosanitary agencies of these importing countries is sometimes too limited to support needed analyses of trade patterns and risk. 

  • U.S. phytosanitary agencies identified less than 10% of the intercepted woodwasps to the species level, whereas Canada identified 25% and New Zealand 75%. Identification of the intercepted woodwasp and its country of origin is critical for effective biosecurity. Nardi et al. (2026) express consternation that only 17.8% of interceptions were identified to species level. Even worse, U.S. phytosanitary officials identified less than 10% of the intercepted woodwasps to species. Canadian officials identified 25%, and New Zealand officials identified 75%. Yes, the taxonomy of the family is complex and in flux. And U.S. port staff must process orders of magnitude more interceptions of woodwasps than do either Canada or New Zealand. However, to understand which species are approaching American borders USDA APHIS (which performs the identifications) needs to provide specialized training and apply modern tools e.g., barcoding, molecular diagnostics. CBP and APHIS must also allow adequate time to process the detection before determining the fate of the shipment.
  • U.S. authorities also did not document the country of origin of 83% of shipments associated with Siricid-infested wood packaging intercepted. New Zealand authorities recorded the country of origin of 78% of intercepted shipments, Canadians of 90%.
  • Lack of information on sampling effort impedes exploitation of valuable info. Haack et al. (2014) discuss this obstacle in detail. Nardi et al. (2026) note that changing inspection and reporting priorities – especially when not explicitly described – hamper analysis of which factors explain variations in interception rates over time.

5) Interceptions of Siricids on wood packaging from regions outside the species’ native range have been increasing since the 1960s. Overall, 2.2% of the 504 interceptions named to species level were imported from countries to which they are not native. This included 12.3% of Sirex noctilio (from North America, the Neotropics, and Africa); 3.2% of Urocerus gigas (from North America and the Neotropics). 

These secondary invasions are often from “bridgehead” populations in the Southern Hemisphere. Nardi et al. (2026) worry that such invasion bridgeheads established in trade hubs could speed up biological homogenization of their region.

6) Only a few of the more than 100 species in the family have established in novel regions although many additional species have frequently been intercepted in wood packaging by port inspectors. The species that have established are Sirex noctilio (introduced from Eurasia to North and South America, Australia, New Zealand, and South Africa); and two North American species: Urocerus albicornis (introduced to Europe and Asia) and Sirex obesus to South America. This pattern suggests that biological, environmental, or dispersal barriers interfere with establishment of other Sirex species even when they are transported to new regions.

exotic pine plantation in New Zealand; photo by Jon Sullivan via Flickr
  • One example might be Sirex juvencus. Although it has been intercepted 215 times by one of the three countries, it has not established outside its native range. Nardi et al. (2026) note that the species prefers spruce (Picea spp.), which are much less commonly planted in Southern hemisphere plantations and around the Northen Hemisphere than the pines (Pinus spp.) that support establishment of S. noctilio and U. gigas.
  • The role of the associated fungi is another factor. Nardi et al. (2026) note that another woodwasp species, Xeris spectrum, has not established in New Zealand despite being intercepted often by that country’s phytosanitary officials and presence of suitable hosts. They note that is species does not transport the symbiotic fungi on its body as do other woodwasps. Instead it oviposits on trees already infested with Amylostereum fungus that was injected by an earlier invasive woodwasp.  (A successful biological control program has reduced infestations of S. noctilio, so pine plantations are again widespread on the islands.)

Nardi et al. (2026) warn about several cryptic dangers. First, horizontal transfer of associated symbiont basidiomycete fungal species has been documented: Amylostereum fungal strains from European S. noctilio to American Urocerus species. Such transfers might increase the pathogenicity of formerly benign introductions. Second, scientists don’t yet understand the probable effects of climate change on insect and fungal species’ life cycles. They mention specifically the Asian species Sirex nitobei because its hosts are widespread Pinus species and it has been detected repeatedly, esp. on dunnage.

Nardi et al. (2026) suggest that officials should consider these ecological factors in assessing the risk of new introductions of specific species. I counter that the underlying rationale for adopting ISPM#15 was recognition that trying to manage individual species or countries of origin would not be effective. Instead, I advocate much more assertive enforcement of the standard.

PSHB damage to Harepephyllum caffrum tree in South Africa; photo by Trudy Paap

Invasive shothole borers

Based on analysis on distribution of haplotypes, phylogenetic relationships and dates of first detections, Lantschner et al. (2026) identified seven independent introduction events of the polyphagous shot hole borer (PSHB) Euwallacea fornicatus: to the continental U.S., Hawai`i, South America, Central Europe, Spain, Türkiye, and South Africa. Most apparently originated directly from the species’ native range, although some evidence of likely secondary spread between already invaded regions. Several of these introductions – Israel (2009), South Africa (2016); Brazil (2020), Argentina and Australia (2021), Spain (2022), Uruguay (2023), and Türkiye (2024) – occurred despite stricter biosecurity measures, specifically ISPM#15.

The United States (California) experienced two additional invasions by Euwallaceae in the 2020s: by PSHB E. fornicatus (in San Jose) and a new species, E. interjectus. This makes a total of nine separate introductions.

Lantschner et al. (2026) suggest two opposite explanations for why so many introductions of this group of species from Asia have continued since ISPM#15 came into effect. Their suggestions are that either beetle populations in China, Taiwan, and/or Vietnam grew, thus increasing the pool of potential invaders/propagule pressure, or that increased international exports from these countries opened new commercial pathways. Certainly the latter has occurred. According to Google, exports from China rose from less than $500 billion in 2003 to ~ $4 trillion in 2025. Exports from Vietnam rose from ~$22 billion to $500 billion over the same period.

To be fair, most consider that the principal pathway for movement of species in the Euwallaceae complex is the trade in ornamental plants. In addition to the introductions listed above, E. fornicatus populations have been detected in greenhouses or botanical gardens in Italy, Germany, the Netherlands, and Poland. All have been reported as eradicated (Lantschner et al. 2026). I recently posted a blog discussing the widespread failure of the international phytosanitary system to stem introductions via this trade.

A second group of scientists (Dell, Xu, and Chi 2026) worry that E. fornicatus has spread especially rapidly in South Africa and South America. Already the outbreak of Fusasrium disease in South Africa is the largest the world: it is present in every province except Limpopo. The disease is recorded on 162 tree species, 78 of which are indigenous to the country (Townsend, Hill, Hurley and Roets 2025).

The introduced ranges – sometimes called bridgeheads – create conditions under which the pest can more easily spread further. Lantschner et al. (2026) suggest that the PSHB population established in southern California could spread into the American southeast, eastern Mexico, and parts of Central America. The population in South Africa might expand into other temperate and subtropical regions of Africa. Beetle populations established in Spain, Israel and Türkiye might spread across Mediterranean basin. Population in Western Australia could spread to eastern regions. They note that achieving some of these dispersals would require crossing substantial gaps of unsuitable habitat. They don’t mention that human transport has moved many populations of wood-boring beetles across unsuitable habitat! As I blogged earlier, officials in Sydney, Australia, determined that 47% of trees in the city are vulnerable to PSHB.

SOURCES

Carnegie AJ, Summerell BA, Trollip C, Tovar F, Smith DI and McDonald J (2026) Sentinel trees for early detection of non-native forest pests and pathogens in AU. Front. For. Glob. Change 9:1801183. doi: 10.3389/ffgc.2026.1801183

Dell, B., W. Xu, and N.M. Chi. 2026. Polyphagous Shot Hole Borer, a Global Threat to Forest Plantations, Green Infrastructure, and Biodiversity: Status, Challenges, and Solutions. Forests 2026, 17, 832

Lantschner, M.V., E. Ceriani-Nakamurakare, A.J. Johnson, A.I. Cognato, S.M. Smith, D.F. Gomez. 2026. Invasion history reconstruction and potential distribution of the ambrosia beetles Euwallacea fornicatus and E. perbrevis (Coleoptera: Scolytinae), two global emerging pests. J Pest Sci 99, 100 (2026). https://doi.org/10.1007/s10340-026-02070-w

Nardi, D., K.E. Wagner, S.F. Ward, A.M. Liebhold, E.G. Brockerhoff, R.M. Turner, J.J. Riggins. 2026. Global movement of woodwasps (Hymenoptera: Siricidae) inferred from border interception records Biol Invasions (2026) 28:167 https://doi.org/10.1007/s10530-026-03881-9

Townsend, G., M. Hill, B.P. Hurley, and F. Roets. 2025. Escalating threat: increasing impact of the polyphagous shot hole borer beetle, Euwallacea fornicatus, in nearly all major South African forest types. Biol Invasions (2025) 27:88 https://doi.org/10.1007/s10530-025-03551-2  

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

Or

https://fadingforests.org