Emerald ash borer – crucial research needs funding!

ash tree dying after attack by emerald ash borer
ash tree dying after attack by emerald ash borer

We all know that the emerald ash borer (EAB) has caused enormous damage in the approximately 25 years since it was first introduced to Michigan and Ontario. (For more information, see writeup here. In brief, EAB has killed “untold millions” of ash trees across more than 170,000 square miles in 25 states and two provinces (map).
Apparently all North American ash are vulnerable – more than 20 species in Canada, the U.S., and Mexico. The genus Fraxinus is one of the most widespread on the continent. These trees’ deaths are causing changes in forest species composition, structure, and function. Hundreds of arthropod species that depend on the genus will be affected.

Nevertheless, forests with important ash components are still outside the infested area and deserve greater protection.


Also, ash trees are among the most common ornamental trees planted in U.S. cities and towns. The death of these trees show us that EAB also has imposed billions of dollars in costs on people who had no direct role in the insect’s introduction and spread. Several studies have proposed estimates:
o Communities in Ohio would likely incur costs up to $4 billion if all ash trees on public land were removed and replaced (Sydnor et al. 2007).
o Communities in four Midwestern states would have to pay an estimated $26 billion to remove and replace as trees growing in parks, private lands, and along streets (Sydnor et al. 2011).
o The cost of treating or removing only half of the affected urban and suburban trees across the anticipated range of EAB during the 10-year period from 2009 to 2019 would be $20 billion (Kovacs et al. 2011).

ash tree killed by EAB; Ann Arbor, MI; courtesy of Major Hefje
ash tree killed by EAB; Ann Arbor, MI; courtesy of Major Hefje

Over the 14 years since EAB was detected, scientists have learned much about the insect, its hosts, and its management. Early detection of new outbreaks remains difficult. However, traps and lures are more effective than even a few years ago. Other new tools also have been deployed, including strategies for protecting high value trees, and slowing the rate of ash mortality in urban and natural forests.

Four biocontrol agents have been released at sites across the invaded area, although it is too early to know how effective they will be in suppressing EAB populations and protecting ash trees.

The systemic insecticide emamectin benzoate controls EAB for up to three years. This means that municipalities and property owners can now save mature ash trees. Studies show that treating such trees costs less than removing dead trees and planting replacements (Herms and McCullough 2014).

Scientists in Ohio, Michigan, Kentucky, and Massachusetts are testing whether treating just some trees in forest settings can help protect nearby ashes.

One of the most important potential responses to this insect is to breed resistant ash trees. The USDA Forest Service and USDA APHIS have funded such efforts since 2005 – only three years after the insect was detected. Scientists have demonstrated that some ash species that have coevolved with the insect in Asia – especially Manchurian ash – are resistant to EAB attack. More recently, they have been studying how to cross-breed the resistant and non-resistant species and how to evaluate the hybrid progeny for genetic resistance.

Dr. Pierluigi (Enrico) Bonello and others at Ohio State and Wright State University  are studying how Manchurian ash trees resist EAB attack. Their focus is on the chemicals present in the trees’ tissues – how they differ in Manchurian ash compared to North American species. These studies have found that Manchurian ash trees contain chemicals that decrease growth and survival of EAB larvae, and decrease the attractiveness of the tree to ovipositing females.
The Ohio team next needs to continue their progress towards identification of the specific chemicals involved, insert the genes that produce them into other ash tree genomes, and produce a large enough number of progeny to test whether the new trees’ genes provide the expected protection.

The team is also studying the other side of this equation – how EAB larvae neutralize defense mechanisms of vulnerable ash species and how these trees may be manipulated to interfere with these adaptations of EAB.. This is a long-term project that needs consistent and sustained support over many years to bring about real capacity for restoring disappearing ash populations.

Unfortunately, funding for this vitally important work is not assured. USDA APHIS (link to 101 on CISP) has funded the team’s work to date, but may no longer be in a position to do so. . After all, it is 14 years since EAB was detected and a decade since APHIS stopped trying to eradicate it. The goal now is to manage EAB in the forest and in urban settings, over the long term. This task logically should fall to the USDA Forest Service.

Both APHIS and the Forest Service are challenged by the need to respond to the introduction of ever more non-native tree-killing insects and diseases; by the need for programs to address pests already present; and by simultaneous reductions in agencies’ budgets. APHIS’ budget for managing all “tree and wood pests” has fallen from $76 million to $55 million since 2011 – a 28% reduction. The USFS’ research budget has fallen less, proportionately: from $307 million to $292 million (a 4% cut).
However, the USFS Research budget has never been generous in funding research on non-native invasive species. Annual totals for invasive species research have been between $5 and $5.6 million since 2012. EAB specifically has been funded at between $1.2 and $1.8 million.
(For a longer discussion of funding shortfalls and other impediments to programs intended to help our forests recover from EAB and other non-native pests, read Chapter 6 of Fading Forests III, available here)

The emerald ash borer is the most destructive and costly forest insect ever introduced to the United States. Surely the government agency responsible for protecting our forests should provide additional resources to counter this threat.

Herms, D. A. and D. G. McCullough. 2014. Emerald Ash Borer invasion of North America: History, biology, ecology, impacts, and management. Annual Review of Entomology, Vol 59, 2014 59:13-30.

Kovacs KF, Mercader RJ,Haight RG, SiegertNW,McCulloughDG,Liebhold AM. 2011. The influence
of satellite populations of emerald ash borer on projected economic costs in U.S. communities, 2010–
2020. J. Environ. Manag. 92:2170–81

Sydnor TD, Bumgardner M, Subburayalu S. 2011. Community ash densities and economic impact
potential of emerald ash borer (Agrilus planipennis) in four Midwestern states. Arboric. Urban For. 37:84–89

Sydnor TD, Bumgardner M, Todd A. 2007. The potential economic impacts of emerald ash borer
(Agrilus planipennis) on Ohio, U.S., communities. Arbor. Urban For. 33:48–54
Posted by Faith Campbell

Support Higher Funding Levels for Key APHIS & USFS Programs

The President’s proposed Fiscal Year (FY)17 budget once again proposes to reduce funding for APHIS and USDA Forest Service. These are the programs that protect our trees and forests; these are the programs that try to prevent introductions of tree-killing insects and disease pathogens, and to counter the damage they cause once introduced.


Congress is expected to act beginning this spring; we need Congress to enact adequate funding for these programs in FY17 – which begins in October.

I provide below the FY15 & FY16 funding levels and the President’s proposed FY17 level. I also suggest more appropriate funding levels for these programs.
Please contact your Representative and Senators by mid-March and ask him or her to support higher funding for these crucial programs. Your voice is particularly important if your Representative or Senator sits on either the Agriculture or Interior Appropriations subcommittees (listed below).
Fiscal Year Funding for Key Programs (funds are given in millions of dollars)

APHIS (I apologize – columns don’t line up!)
FY15       FY16       FY17 (Pres’ request)             $needed

Plant Health (total)       305         314           288
Specialty crops               156        164           146            164
Tree & wood pests           54          54              46               54

The “Tree & wood pests” account funds all APHIS efforts to contain or eradicate the Asian longhorned beetle and emerald ash borer; much smaller programs targeting walnut twig beetle/thousand cankers disease, laurel wilt, and polyphagous shot hole borer [all described here as well as the agency’s involvement in firewood and other slow-the-spread campaign. Even at the $54 million funding level, APHIS is already ignoring many established pests … and its ability to respond to new introductions is severely restricted. With the continuing presence of damaging wood-borers in incoming crates and pallets (See earlier blogs discussing the wood packaging pathway posted in August, September, and October; and Chapter IV of Fading Forests III, now is not the time to cut funding for this program.

The “specialty crops” account includes a small amount of funding (in past years, approximately $5 million) to support APHIS’ program aimed at preventing spread of sudden oak death through movement of nursery stock. (For discussions of this risk see my earlier blogs from July and August and Chapter IV of Fading Forests III.

The budget justification notes that “cooperators who directly benefit from … activities [under the Tree and Wood Pests and Specialty Crop Pests programs] will need to increase contributions to achieve the same level of program operations. Even with the proposed decreases, APHIS will continue to pay between 47 percent and 80 percent of the costs of the programs. …” The Office of Management and Budget has long tried to reduce the federal share of pest containment costs.  I counter: is it not appropriate that the agency with the legal responsibility for preventing and containing pest introductions bear the cost of responding when pests are introduced nevertheless?

Fiscal Year Funding for Key Programs (funds are given in millions of dollars)

USFS  (I apologize – columns don’t line up!)
FY15        FY16        FY17 Pres’ request        needed
Forest Health Protection (total)

104.57         99.6             92.06           100?
Federal lands    58.922        58.922       51.382
Coop lands         45.655        40.678       40.678         48
FHP funds the Forest Service’ assistance to federal partners (e.g., National Park Service) and non-federal entities (e.g., states, cities, private land managers) for management of forest pests – both native and alien species. The FY17 budget justification does not provide a breakdown of spending by species. The FY16 President’s request allocated only $12 million (13% of total funds) to specific projects targeting non-native insects or pathogens. More than $7 million of these funds went to just one species – European gypsy moth. Please advocate for a higher proportion to go to non-native pests.

Research (total)                              296       291        291.982            300?
Forest Inventory                              70          75                   77               83

The USFS Research and Development program provides most of the funds for research to understand non-native pests’ pathways of introduction and spread and biological impacts. These funds also support most of the efforts to breed resistance into tree species and some of the work on other control methods, such as chemicals and biocontrol. The FY17 budget justification does not provide a breakdown of spending by species; the FY16 President’s request allocated only $5 M (less than 2% of total funds) to projects targeting non-native insects or pathogens. Please advocate for a higher proportion to go to non-native pests.

Members of key House & Senate Appropriations Subcommittees
Agriculture Appropriations Subcommittees (fund APHIS):
House: Aderholt (AL), Yoder (KS), Rooney (FL), Valadao (CA), Harris (MD), Young (IA); Farr (CA), DeLauro (CT), Bishop (GA), Pingree (ME)
Senate: Moran (KS), Blunt (MO), Cochran (MS), McConnell (KY), Collins (ME), Hoeven (ND), Daines (MT), Merkley (OR), Feinstein (CA), Tester (MT), Udall (NM), Leahy (VT), Baldwin (WI)

Interior Appropriations Subcommittees (fund USFS):
House: Calvert (CA), Simpson (ID), Cole (OK), Joyce (OH), Stewart (UT), Amodei (NV), Jenkins (WV); McCollum (MN), Pingree (MD), Kilmer (WA), Israel (NY)
Senate: Murkowski (AK), Alexander (TN), Cochran (MS), Blunt (MO), Hoeven (ND), McConnell (KY), Daines (MT), Cassidy (LA); Udall (NM), Feinstein (CA), Leahy (VT), Reed, Tester (MT), Merkley (OR)

Posted by Faith Campbell

How should regulators address strains of pathogens?

Species of tree-killing pathogens can have several “strains” that may vary in virulence or hosts affected.

`ohi`a`ohi`a tree on Hawai`i

This is a phenomenon well known to pathologists, but regulators have not adapted their programs to address it. Once a pathogenic species is determined to be established in the country, APHIS considers the entire species to be “non- actionable” and will not attempt to prevent introduction of any new strains. As the examples below illustrate, allowing introduction and spread of new strains poses risks to North America’s trees.

World-renowned British forest pathologist Clive Brasier has spoken out often on the risk posed by various strains of a pathogen. He has also written about the potential for pathogen species to hybridize and for that hybrid to threaten new hosts.

How widespread a problem is this? Some of the pathogens causing the greatest damage have several strains that vary in their virulence and host range.

  •  The sudden oak death pathogen, Phytophthora ramorum is known to have four strains: NA1, NA2, EU1 and EU2. The EU1 lineage has primarily been found in European nurseries and forests. It has also been recovered from several nurseries and waterways on the U.S. west coast. Last year, the EU1 lineage was detected in a forest in Oregon (see my blog posted 15August 2015). This is troubling for two reasons:
    * the EU1 lineage is more aggressive than the NA1 lineage already present in the forests of California and Oregon. Some of the individual tree which now appear to be resistant to the NA1 lineage might succumb to the EU1 lineage.
    * The EU1 and NA1 lineages belong to opposite mating types, so they can potentially reproduce, thereby increasing the genetic variability of the pathogen. (Sexual reproduction in P. ramorum can only occur when opposite mating types meet; in the absence of opposite mating types, all reproduction is clonal.)

• The guava rust or myrtle rust pathogen, Puccinia psidii, also has several strains which vary in their virulence. Already, a new strain introduced to Jamaica in the 1930s caused extensive damage to the allspice industry – although a different strain had been on the island for decades (Carnegie 2016).

Hawaiian conservationists worry that a more virulent strain of P. psidii might be introduced and threaten additional species of Myrtaceae on the Islands – especially the `ohi`a tree which is the major canopy tree in 80% of the Islands’ remaining native forest. These forests are key to maintaining the Islands’ watersheds and biodiversity, especially because `ohi`a nectar is the principal food source for many of the remaining native and rare bird species. (See writeup here)

Multiple strains of `ohi`a rust have been identified in the pathogen’s native range of Brazil. Using funds from the USDA Forest Service, scientists in Brazil (Costa da Silva et al. 2014) tested five of the strains; three proved to be highly virulent on most `ohi`a seedlings tested. `Ohi`a from several locations were tested; none showed significant resistance to these three strains of the P. psidii pathogen.

The tests were carried out under conditions highly conducive to infection, so the results cannot be used to predict epidemiological behavior and ecological ramifications in natural conditions. Nevertheless, the results do support the need for greater efforts to prevent introduction of new strains to the Islands.

Additional tests are under way to determine whether the Brazilian strains are more virulent than that strain currently found in Hawai`i and to learn more about possible variation in vulnerability among `ohi`a trees from a greater variety of sites.
• The pathogen that causes Port-Orford cedar root disease (Phytophthora lateralis) has now been found to have four lineages. Scientists compared isolates from the pathogen’s putative native range on Taiwan to isolates from the North American west coast (where it has been established since early in the 20th Century) and Europe (where it began killing trees in the 1990s). They found one slow- growing strain from Taiwan, one fast-growing strain from North America and Europe, and one of intermediate growth from a small area of the United Kingdom (Brasier et al. 2012).

Sometimes, pathogens behaving in unexpected ways are initially thought to be a strain or lineage, but are later classified as a novel species. Thus the Ceratocystis causing `ohi`a wilt was initially thought to be a strain of C. fimbricata, a widespread fungus that has been on the Hawaiian Islands for decades. Scientists now think it is a new species (Keith 2016).

Pathogens are difficult to manage. The vast majority of species remain undescribed. They are difficult to detect until they cause noticeable damage. For a longer discussion of the challenges posed by pathogens and other unknown organisms, read Chapter 3 of Fading Forests II, available here.

However, the great threat to our forests necessitates that APHIS and other phytosanitary agencies (in states and around the world) develop improved methods for addressing the challenge that pathogens pose. Our forests simply cannot afford introductions of more tree-killing fungi, oomycetes, and other pathogens.

At a minimum, APHIS should respond to evidence that a particular pathogen is composed of multiple strains with varying virulence by agreeing to designate such novel strains as “actionable” and applying all its authorities and powers to prevent introduction and spread of the novel strains.

As I noted in my blog of earlier this month, APHIS also needs to develop more effective strategies for addressing introduction and spread of pathogens generally. USDA should assist such efforts to improve controls over pathogens by bringing about prompt finalization of two APHIS initiatives:
1) Prohibiting temporarily plants suspected of transporting known damaging pathogens. This action is allowed under the NAPPRA (not authorized for importation pending pest risk assessment) program.
2) Requiring foreign suppliers of living plant imports to implement “hazard analysis and critical control point” programs to ensure that the plants are pest-free during production and transport. This approach is allowed under ISPM#36 and would be authorized under pending changes to APHIS’ “Q-37” regulation. (See Federal Register Vol. 78, No. 80 April 25, 2013.)

(See longer discussions of these programs in Fading Forests III, available here.)

Clive M. Brasier, C.M, S. Franceschini, A.M. Vettraino, E.M. Hansen, S. Green, C. Robin, J.F. Webber, and A.Vannini. 2012. Four phenotypically and phylogenetically distinct lineages in Phytophthora lateralisFungal Biology. Volume 116, Issue 12, December 2012, Pages 1232–1249

Carnegie, A.J., A. Kathuria, G.S. Pegg, P. Entwistle, M. Nagel, F.R. Giblin. 2016. Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia. Biol Invasions (2016) 18:127–144 DOI 10.1007/s10530-015-0996-y

Costa da Silva, A., Magno Teixeira de Andrade, P. Couto Alfenas, A., Neves Graca, R., Cannon, P., Hauff, R., Cristiano Ferreira, D., and Mori, S. 2014. Virulence and Impact of Brazilian Strains of Puccinia psidii on Hawaiian `Ohi`a (Metrosideros polymorpha). Pacific Science (2014), vol. 68, no. 1:7-56
Keith, L. 2016. Ceratocystis fimbriata, Rapid O’hi’a Death: Unraveling the mystery. 27th USDA Interagency Research Forum on Invasive Species January 12-15, 2016 Annapolis, Maryland


Posted by Faith Campbell

How should APHIS manage pathogens with Multiple Hosts?

large redbay tree on Jekyll Island, Georgia; killed by laurel wilt

Horton House w redbay


North America and other continents have been invaded by a growing number of tree-killing organisms – primarily pathogens – that attack a wide range of hosts100 species or more. Examples include sudden oak death / Phytopthora ramorum**, laurel wilt**, and the Fusarium fungus transported by the polyphagous and Kushiro borers**. These pathogens are more difficult to manage because of the range of potential hosts. Furthermore, a single introduced species can threaten numerous host species across large areas.
This is not a new phenomenon. Root rot caused by Phytophthora cinnamomi reached North America in the late 18th or early 19th Century, where it eliminated chestnut and chinkapin from low-elevation sites. P. cinnamomi is found in countries around the world. In Australia, it is killing a wide range of trees and shrubs across several plant families that constitute important components of Australia’s flora, including Myrtaceae, Proteaceae, Epacridaceae and Papilionaceae. There have been significant ecological impacts to plant communities and dependent wildlife in southeast and southwest Australia (Carnegie et al. 2016).

Nevertheless, the apparent proliferation of tree-killing organisms with multiple vulnerable hosts is troubling. So is the rapidity with which these organisms have been spread to distant places.

The disease called variously guava, eucalyptus, or myrtle rust – caused by Puccinia psidii** – attacks plants in “only” one family – the Myrtaceae. Its host list now includes more than 450 species in 73 genera. More than 200 of these are native species in Australia – where more than 10% of the plant species are members of this family. At least some of these plants are highly vulnerable to the rust; more than half of the individuals of the small tree Rhodomyrtus psidioides surveyed in a recent study were dead less than four years after the pathogen was introduced (Carnegie et al. 2016). New Zealand also has large numbers of Myrtaceae.

Guava rust is believed to be native to South and Central America. It was introduced to the Caribbean and southern Florida by the first decades of the 20th Century. Recently, the pathogen began to move. A new strain arrived in Florida in the 1990s. The rust was detected in Hawai`i in 2005. There, it is killing the native endangered shrub Eugenia koolauensis and an invasive shrub Syzygium jambos. In the past decade, guava rust has also invaded Japan, China, Australia, South Africa and New Caledonia (Carnegie et al. 2016).

Laurel wilt** also attacks “only” one plant family, the Lauraceae. While the United States is home to a relatively small number of plants in this family, Central America is a center of endemism for the family. In the United States, concern has focused on the disease’s threat to the avocado industry. However, the pathogen’s principal wild host, redbay, is likely to be virtually eliminated from U.S. forests except as seedlings too small to be attacked. (One ray of hope: Professor Jason Smith at the University of Florida is making progress on breeding redbays resistant to the disease.) Given the large number of presumably vulnerable trees and shrubs in Mexico and Central America, the spread of laurel wilt into Texas is worrisome.

Other pathogens attack shrubs and trees across several families. I noted Phyotphthora cinnamomi above. Other Phytophthoras share this ability.

Phytophthora ramorum** has a host list exceeding 130 herbaceous, shrub, and tree species in families ranging from maples to rhododendrons, oaks to hemlocks. P. ramorum is established in coastal parts of California and southern Oregon; and in western United Kingdom and Ireland. Another Phytophthora, P. kernoviae,** has a similarly broad host range. It is also established in the United Kingdom.

Fusarium dieback is caused by the fungus Fusarium euwallacea, which is transported by two beetles in the Euwallacea genus, called the polyphagous** and Kushiro shot hole borers. The beetle is known to attack more than 300 species of trees, shrubs, and vines in more than 58 plant families; hosts include species of oaks, maples, sycamores, hollies, and willows.

These multi-host pathogens are extremely difficult to contain – or even to detect early in the invasion. Australia tried to contain Puccinia rust, but conceded failure after only a few months. USDA APHIS does not have containment programs for any of three pathogens described here – despite the danger they pose to trees and other native vegetation.

Industry groups sometimes fund efforts to protect their crops. Avocado growers have spurred research on both laurel wilt and the Fusarium fungus — threats to their crop. However, academic researchers working on the impacts of laurel wilt on native ecosystems must scramble for funds. This is exactly the kind of research that requires – and deserves – increased public funding.

What should be done? Phytosanitary agencies need to improve greatly programs aimed at preventing introduction of pathogens to naïve hosts in new geographies. For the U.S., APHIS has already advocated two important improvements:
1) Prohibiting temporarily plants suspected of transporting known damaging pathogens. This action is allowed under the NAPPRA (not authorized for importation pending pest risk assessment) program.
2) Requiring foreign suppliers of living plant imports to implement “hazard analysis and critical control point” programs to ensure that the plants are pest-free during production and transport. This approach is allowed under ISPM#36 and would be authorized under pending changes to APHIS’ “Q-37” regulation. [See Federal Register Vol. 78, No. 80 April 25, 2013]

(See longer discussions of these programs in Fading Forests III, available here.)

Unfortunately, implementation of both of these programs has stalled. A list of plants proposed in May 2013 for NAPPRA restrictions has still not been finalized. Revisions to the Q-37 regulation proposed in April 2013 have also not been finalized.

USDA leadership should promptly implement these long-delayed improvements.
** indicates those pathogens and insect/pathogen complexes that are described briefly here 


Carnegie, A.J., A. Kathuria, G.S. Pegg, P. Entwistle, M. Nagel, F.R. Giblin. 2016. Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia. Biol Invasions (2016) 18:127–144 DOI 10.1007/s10530-015-0996-y

Posted by Faith Campbell