forest pathogens – Page 16 – Center for Invasive Species Prevention

Threats to America’s Magnificent Oaks

Oak trees are immensely symbolic to many people and many are magnificent. Congress even designated the red oak as America’s “national tree”.

Photo of Q. rubra leaves by Becca MacDonald, Sault College; www.bugwood.org

Of course, there are many kinds – from those that span many states to those that grow in just some special areas. USDA’s Plants database lists more than 300 native species for the U.S. alone. Many provide substantial ecosystem services and all parts of the country would be poorer without them.

Despite our oaks’ importance, we are doing far too little to protect them from the full range of non-native insects and diseases that pose threats.

CURRENT THREATS IN THE EAST

In the East (from the Atlantic to the Great Plains), oaks are under attack from at least four non-native pests:

One of these, the European gypsy moth (Lymantria dispar), is the target of major containment and suppression programs operated by USDA Animal and Plant Health Inspection Service (APHIS), the US Forest Service and the states. In fact, the US Forest Service spends half of its entire budget for studying and managing non-native pests on the European gypsy moth. In part, this is because the European gypsy moth is so widespread, with outbreaks from Nova Scotia to Wisconsin and south across eastern Ohio to Virginia. (See the map of EGM range here). It also attacks a wide range of tree and shrub species.

But other oak-killing insects and diseases, some with the potential to be at least as damaging, receive far fewer resources.

Oak wilt (caused by the fungus Ceratocystis fagacearum) is widespread from central Pennsylvania across Iowa, down the Appalachians in West Virginia and North Carolina-Tennessee border, in northern Arkansas and with large areas affected in central Texas. There is an isolated outbreak in New York State. (See map here). According to the US Forest Service, oak wilt is one of the most serious tree diseases in the eastern U.S. It attacks primarily red oaks and live oaks. It is spread by both bark-boring beetles and root grafts.

From Long Island along the coast into Nova Scotia and into central Massachusetts, oaks are being killed by the winter moth (Operophtera brumata). Like the gypsy moth, the winter moth has a wide host range. (For more information, see here). A small program led by Joseph Elkington of the University of Massachusetts has focused on biocontrol. Biocontrol agents have successfully reduced winter moth damage in Nova Scotia and the Pacific Northwest. First results are promising in New England.

CURRENT THREATS IN THE WEST

In the West, millions of oaks have been killed by several pathogens and insects that are established and spreading; and additional threats loom.

Coast live oaks, canyon live oaks, California black oaks, Shreve’s oaks, and tanoaks growing in coastal forests from Monterey County north to southern Oregon that catch fog/rain are being killed by sudden oak death and here. Sudden oak death has killed over one million tanoaks as well as hundreds of thousands of coast live oaks and other trees. In early days of the infestation, Oregon – with considerable help from the US Forest Service – tried to eradicate a small infestation in Curry County. The inherent difficulty in managing a pathogen and interruptions in funding caused that effort to fail. The state is now focused on trying to slow spread of the disease.

In California, coast live oaks, black oaks, and canyon oaks in the southern part of the state – primarily in San Diego County, but also parts of San Bernardino, Orange, and Los Angeles counties – are being killed by goldspotted oak borer and here. At least 100,000 black oaks have been killed in less than 20 years. Neither the State of California nor USDA APHIS has adopted regulations aimed at preventing spread of the goldspotted oak borer, despite oaks being at risk throughout California.

Two more wood-boring beetles threaten oaks in southern California. In five counties in the region, coast live oaks, canyon live oaks, Engelman oaks, and valley oaks – and many other kinds of trees – are being killed by a disease transmitted by the polyphagous and Kuroshio shot hole borers and here. The polyphagous and Kuroshio shot hole borers attack more than 300 plant species, including tree species that anchor the region’s riparian areas as well as half of the trees planted in urban areas of the region.

Also, oaks on the West coast would be attacked by gypsy moths should they reach the area. The risk is two-fold – the Asian gypsy moth continually is carried to the area on ships bearing imports from Asia (as discussed in my blog in March). And the European gypsy moth is sometimes taken across the country on travellers’ vehicles, outdoor furniture, or firewood. Both the West Coast states and USDA search vigilantly for any signs of gypsy moth arrival.

Or course, other non-native pests can also be introduced or spread to new, vulnerable, areas. I have blogged about the risk to the East from sudden-oak-death infested plants moving in the nursery trade (see blogs from July 2015). The polyphagous and Kuroshio shot hole borers might also threaten forests in other warm regions of the country such as the Gulf Coast, where some known and potential host trees grow.

ADDITIONAL THREATS

Two apparent threats have come to our attention recently: fungi in the genus Diplodia and another disease called foamy bark canker. There is some uncertainty whether the insects or pathogens are non-native. Both are apparently closely linked to drought stress.

two Diplodia fungi – Diplodia corticola and quercivora – have been detected in both Florida and California. These fungi were previously known to kill oaks in the Mediterranean region.

According to Mullerin and Smith (2015), one or both of these fungi might be native to North America. Diplodia corticola was first identified in the 1980’s in cork oaks (Quercus suber L.) in Mediterranean countries. It has since been determined to be the cause of mortality in other species of European oaks. D. corticola was first reported in California in 1998 in coast live oak trees (Q. agrifolia) that had been colonized by bark and ambrosia beetles. There, it has been an important factor in the deaths of thousands of acres of coast and canyon live oaks (Q. chrysolepis) since 2002 (Mullerin and Smith 2015). In California, periodic diebacks since the late 1970s have been associated with droughts. Symptoms have mainly shown up in coast live oak (Q. agrifolia), black oak (Q. kelloggii), and valley oak (Q. lobata). Dieback is noticeable in at least 20 California counties, throughout most of the range of coast live oak. (See here.)

The first detection of D. corticola in southern Florida was in 2010; D. quercivora was detected in 2013. In Florida, these fungi attack live oaks (Quercus virginiana). Almost all the symptomatic trees in Florida grow in cultivated settings where they are exposed to various stresses. In addition, most of the state experienced severe drought in 2010, the year reports of dieback began (Mullerin and Smith 2015).

Host range studies indicate that 33 species of oaks and one species of chestnut that grow in the Southeast are vulnerable, to varying degrees, to D. corticola. Oaks in the red oak group (Section Lobatae) are more vulnerable than are white oaks (Section Quercus) (Mullerin and Smith 2015). In the test, the most vulnerable appear to be the following species native to the Southeast: Q. laurifolia, Q. virginiana, Q. geminata, Q. chapmanni, Q. laevis (turkey oak), Q. phellos, Q. pumila, and Q. incana. (source: poster presented by Dreaden, Black, Mullerin, Smith at the 2016 USDA Invasive Species Research Forum.)

It is unknown how Diplodia corticola & Diplodia quercivora colonize oaks. However, members of the family (Botryosphaeriaceae) generally enter plants through wounds, including leaf scars, or stomata open for gas exchange. They often live harmlessly as endophytes within the plant, becoming pathogenic when the plant is stressed by environmental factors such as drought, flooding, heat, freezing, herbicide use, or soil compaction (Mullerin and Smith 2015).

Foamy bark canker is new disease of oak species caused by a newly discovered species of species of fungus (Geosmithia pallida). The pathogen is vectored by the Western oak bark beetle (Pseudopityophthorus pubipennis). The disease complex has great potential to cause extensive damage to oaks in California. Still little is known about the disease’ overall distribution, establishment and incidence.

Declining coast live oak trees have been observed since 2012 throughout urban landscapes in Los Angeles, Orange, Riverside, Santa Barbara, Ventura, and Monterey counties in California. Fungal colonies were observed within beetle galleries (Lynch et al. 2014). The Western oak bark beetle is thought to be a native. It commonly attacks trees weakened by other agents; it has not previously been associated with disease. However, the disease vector might be a different, similar beetle; scientists are collecting more, from a larger geographic area, to determine whether it is the native species or something else. In Europe, the fungus appears to have be associated with a range of bark-boring insects and is widely distributed. There is no previous published record of the fungus occurring in the United States (Lynch et al. 2014).

Symptoms can be viewed here.

SOURCES

Dreaden, T. A. Black, S. Mullerin, and J. Smith risk to oaks from Diplodia cor+cola and D. quercivora, two emergent fungal pathogens (poster at Annapolis 2016) Includes map showing distribution in Florida.

Drill,S. New pest alert for Foamy Canker Disease on Coast Live Oak. 2014. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13707

Lynch, S.C., D.H. Wang, J.S. Mayorquin, P.F. Rugman-Jones, R. Stouthamer, A. Eskalen. 2014. First Report of Geosmithia pallida Causing Foamy Bark Canker, a New Disease on Coast Live Oak (Quercus agrifolia), in Association with Pseudopityophthorus pubipennis in California. APS Journals Plant DiseaseSeptember 2014, Volume 98, Number 9 Page 1276 http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-03-14-0273-PDNhttp://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-03-14-0273-PDN

Lynch, S., S. Rooney-Latham, A. Eskalen. [DATE?] Foamy Bark Canker A New Insect-Disease Complex on Coast Live Oak in California Caused by Western Oak Bark Beetle and Geosmithia sp.

Mullerin, S. & J.A. Smith. 2015. Bot Canker of Oak in FL Caused by Diplodia corticola & D. quercivora. Emergent Pathogens on Oak and Grapevine in North America. FOR318

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 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.)
Sources

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; afterwards killed by laurel wilt

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

Source

Posted by Faith Campbell

Hawaii’s unique forests now threatened by insects and pathogens – APHIS & State should act

We have known since Darwin that oceanic islands can be cradles of speciation & endemism. Hawai`i exemplifies the phenomenon. Ninety-eight percent of native flowering plants are endemic (Cox). The density of native insect species in Hawai`i is higher than on mainland North America (Yamanaka).

We have known since Elton or earlier that oceanic islands are highly vulnerable to bioinvasion because their unique species did not evolve defenses against predation, herbivory, competition, or diseases; or the ability to adapt to changed soil chemistry or increased fire frequency.

Chapter 8 of the Office of Technology Assessment study of harmful invasive species states:

“Hawaii has a unique indigenous biota, the result of its remote location, topography, and climate. Many of its species, however, are already lost, and at least one-half of the wild species in Hawaii today are non-indigenous. New species have played a significant role in the extinction of indigenous species in the past and continue to do so. Hawaii, the Nation, and the world would lose something valuable as the indigenous fauna and flora decline.”

I apologize for not addressing the disasters wreaked on Hawai’i’s fauna and non-arboreal flora by invasive mammals and birds, plants, and such animal diseases as avian malaria and avian pox. For more on these topics, see the other sources listed below and the websites maintained by the Hawai`i Invasive Species Council and Coordinating Group on Alien Pest Species. Cox notes that alien species span all trophic groups and threaten the complete replacement of the native terrestrial biota.

Outside of land clearing for ranches and other uses, much of the damage to Hawaii’s native forest trees has been caused by introduced mammals – especially pigs and goats; and invasive plants. Few of the enormous number of non-native insects that have established in Hawai`i appear to have attacked native trees. More than 2,600 non-native insects have been introduced; their number equals three-quarters of the NIS insects established in North America, yet Hawai`i constitutes less than 0.01% of the area of North America. The ratio of non-native to native insect species is higher for Hawai`i than for the other geographic areas studied by Yamanaka and colleagues (mainland North America, “mainland” Japan, and two offshore Japanese islands) (Yamanaka).

More than 13% of the non-native insects (=~350) in Hawai`i were introduced intentionally for biological control of agricultural pests and non-native plants (Yamanaka). Cox, Elton, and the Office of Technology Assessment discuss briefly the sometimes damaging effects of these deliberate introductions.

I am aware of only one NIS insect that has seriously threatened a native tree species: the Erythrina gall wasp, which killed many native wiliwili trees as well as lots of introduced coral trees planted in towns and as windbreaks. Biocontrol agents have helped prevent continuing damage from the gall wasp.

Disease pathogens have so far proved greater threats to Hawaiian native trees than introduced insects. Koa wilt is killing koa, especially at lower elevations. It is not certain whether the pathogenic Fusarium fungus is introduced or native; it has been found on all four major islands. Koa is second only to `ohi`a (see below) in abundance in mid to upper elevation Hawaiian forests. It is extremely important ecologically and culturally (koa was the tree from which large, ocean-going canoes were made). Koa also has a wood valued for a range of uses.

`Ohi`a lehua is the most widespread tree on the Islands, dominating approximately 80% of Hawai`i’s remaining native forest (about 965,000 acres, 1500 square miles). These forests are home to Hawai`i’s one native mammal (Hawaiian hoary bat) and 30 species of forest birds (Loope and LaRosa). One threat to `ohi`a comes from `ohi`a or eucalyptus rust. Detected in April 2005, it had spread to all the major islands by August. Fortunately, the strain of `ohi`a rust established in Hawai`i is not very virulent on `ohi`a, but it has killed many plants of an endangered native shrub, Eugenia koolauensis and in Australia it has killed many plants in the Myrtaceae family. Hawaiian conservationists worry that a different, more virulent, strain might be introduced on plants or cut foliage shipped to the Islands from either foreign sources or the U.S. mainland.

A new, apparently more damaging, pathogen was detected in 2010. This new disease is caused by two newly discovered species of the fungal genus Ceratocystis — Ceratocystis lukuohia and C. huliohia. By October 2015 the disease has killed 50% of the `ohi`a trees in several scattered locations totaling 6,000 acres on the southeast lowlands of Hawai`i (the “Big Island”). Tree mortality was nearing the boundary of Hawaii Volcanoes National Park. Hawaii Volcanoes pioneered methods for controlling invasive pigs and plants that threatened to destroy the Park’s forests. Through 40 years of sustained effort, Hawaii Volcanoes has brought those threats under control. Now the Park faces loss of its invaluable `ohi`a forest to this pathogen – which will be infinitely harder to keep out of the Park. (For updates on “rapid ohia death” visit the write-up here.)

The Hawai`i Department of Agriculture has adopted an emergency regulation aimed at preventing transport of infected wood or tree parts from the Big Island to other islands.

Although tree-killing insects and pathogens have so far not been as damaging in Hawai`i as might be expected, the Islands are highly vulnerable due to the large volumes of cargo and people from around the globe which land on the Islands and the few tree species native there. The Erythrina gall wasp has island-hopped from the east coast of Africa to Hawai`i and many islands in between. `Ohi`a rust is native to tropical America and probably reached the islands on cut stems used in floral decorations. It is unknown where the Ceratocytis fimbriata strain evolved or how it reached Hawai`i.

USDA APHIS is responsible for preventing introduction of new plant pests to Hawai`i from non-U.S. jurisdictions (as well as from Guam). APHIS has traditionally paid little attention to plant pests that are thought likely to threaten “only” Hawai`i but not plant (agricultural) resources on the mainland.

Hawaiian authorities are responsible for preventing introductions from the Mainland – but they struggle with inadequate resources to address the huge volumes of incoming freight and they sometimes hesitate to act. (Hawai`i Department of Agriculture considered restricting shipments of foliage in the Myrtacea to minimize the risk of introduction of a new strain of `ohi`a rust, but in the end did not adopt such a measure.)

Hawai`i’s unique biota is an irreplaceable treasure. All Americans should act to prevent introduction additional introductions to the Islands.

SOURCES:
Cox, George W. Alien Species in North America and Hawaii Impacts on Natural Ecosystems 1999
Elton, Charles S. The Ecology of Invasions by Animals and Plants 1958; see especially Chapter 4: The Fate of Remote Islands
Loope, L. and LaRosa, A.M. `Ohi`a Rust (Eucalyptus Rust) (Puccinia psidii Winter) Risk Assessment for Hawai`i
U.S. Congress Office of Technology Assessment. 1993. Harmful Non-Indigenous Species In the United States. OTA-F-565; available at http://govinfo.library.unt.edu/ota/Ota_1/DATA/1993/9325.PDF

Yamanaka, T., N. Morimoto, G.M. Nishida, K. Kiritani, S. Moriya, A.M. Liebhold. 2015. Comparison of insect invasions in North America, Japan and their Islands. Biol Invasions DOI 10.1007/s10530-015-0935-y

Posted by Faith Campbell

Wood Packaging – Customs Efforts & Recent Detections

As noted in my blog of July 15, damaging pests continue to enter the country in wood packaging. The most comprehensive study indicates that tree-killing pests are found in an estimated 13,000 containers entering the country each year – or 35 per day.
These pests are present despite requirements adopted 9 or more years ago that wood packaging be treated.

Types of cargo packaged in wood are inspected by agricultural specialists within the Bureau of Customs and Border Protection , a division of the Department of Homeland Security. CBP agricultural specialists work at 167 sea, air and land ports of entry. See an article about CBP efforts to curb introductions of tree-killing pests posted at http://www.cbp.gov/frontline/2014/12/frontline-december-forest-prime-evil.

CBP agriculture specialists in Laredo, Texas, examine a wooden pallet for signs of insect infestation. [Note presence of an apparent ISPM stamp on the side of the pallet] Photo by Rick Pauza

According to the CBP in the above article, the types of commodities imported that have the highest rates of SWPM-related pest interceptions are metal and stone products (including tile), machinery (such as automobile parts and farm equipment), electronics, bulk food shipments and finished wood articles.
These imports have a long-standing record of pest presence – as described in Chapter 4 of my lengthy report on tree-killing pests.

According to the CBP , 48% of the wood packaging entering the country that does not comply with the treatment requirements comes from Mexico. Mexican maquiladoras are factories that import material and equipment duty-free, then assemble a wide range of products – auto parts, apparel, electronics, furniture, and appliances. Mexico’s 3,000 maquiladoras account for half of Mexico’s exports.
China has the second worst record.
Of course, we import lots of stuff from both countries! However, the China situation is particularly disturbing because the U.S. has required that wood packaging from China be treated since the beginning of 1999 – 16 years!
The ports receiving highest numbers of shipments with non-compliant wood packaging materials have consistently been those along the U.S.-Mexico border, especially in Texas: Laredo, Pharr, more recently Brownsville & Houston. Other ports receiving high volumes of non-compliant wood packaging include Blaine, Washington; Long Beach, California; and Romulus, Michigan.

USDA APHIS and CBP have cooperated in a program under which insect larvae found in wood packaging are identified as to species. In recent years, they have studied larvae detected in wood packaging from eight ports – Long Beach, Seattle; 2 ports in Florida; and three cities on the Texas-Mexico border. (Remember, there are 167 ports of entry across the country, so this sample represented 5% of all ports.) Found at these ports were an unreported total of insects, including 116 individuals in the same family as Asian longhorned beetle (Cerambycids). Forty-three were from China (including 5 ALB), 20 from Russia, and seven from Mexico (Philip Berger, APHIS, at the annual meeting of the Continental Dialogue on Non-Native Forest Insects and Diseases, November 2014)

Most familiar – and frightening! – examples of pests introduced via wood packaging include Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle and its accompanying fungus, and possibly polyphagous shot hole borer and its accompanying fungus – all described here.

The prospect of receiving additional insects from Asia scares everyone. What if a new pest is as bad as the four we already have? The emerald ash borer has already caused the removal of an estimated 50 million trees and continues to spread to ash trees – and now white fringe trees – throughout America east of the Great Plains. Laurel wilt disease (transmitted by the redbay ambrosia beetle) is rapidly eradicating redbay trees in the southeast, including in Everglades National Park – one of the icons of the American conservation movement. The Asian longhorned beetle has already caused removal of more than 124,000 trees from our cities, suburbs, and nearby woodlands – at a cost to federal taxpayers of more than $500 million. If it escapes eradication programs, it threatens trees in 10% of America’s forests. The polyphagous shot hole borer threatens numerous tree species that, collectively, make up more than half the trees planted in urbanareas in Southern California.

While no one denies the threat from insects native to Asia, we should not be complacent about insects from Mexico. Although we are neighbors, our forests are separated by deserts – allowing insects to evolve there to which our trees are vulnerable. Three wood-boring beetles native to Mexico and possibly some U.S. border states are already causing havoc to U.S. trees – goldspotted oak borer, soapberry borer, and walnut twig beetle and its accompanying fungus (all described here). The first two were introduced to vulnerable forests through movement of firewood, not wood packaging. The third – the walnut twig beetle – might be native to California, although thousand cankers disease is killing native California walnuts throughout the state so something is different than it used to be.

goldspotted oak borer

When Customs officials detect wood packaging that does not comply with ISPM #15 (“noncompliance” means one of three things: the wood does not bear the ISPM #15 stamp; or the stamp appears to be fraudulent; or signs of pests are detected), that wood must be re-exported immediately, usually with the associated commodity. If any insects present pose an immediate risk of introduction, e.g., if adults are emerging, the shipment might need to be fumigated before re-export.
Re-exported shipments – and any treatments – cause importers to lose income and face costly delays. Still, the continuing presence of non-compliant wood packaging indicates that these inconveniences are insufficient to prompt importers to take all precautions possible to ensure that packaging used by their suppliers and brokers comply with the requirements.

Why don’t importers use alternative packaging made from plastic, steel, or composites that would not harbor tree-killing insects? Plastic pallets also weigh much less than wooden ones, so transport costs are reduced. Customs has pointed out the advantages. … Still, packaging material made from wood is comparatively plentiful, cheap, easy to repair, biodegradable. So it continues to dominate the market.
What steps can be taken by the U.S. government and importers to minimize the presence of insects in packaging?
• U.S. policy allows an importer to be caught 5 times in 1 year with wood packaging that does not comply with the regulatory requirements. Requirements adopted a decade or more ago should be enforced strictly! The Bureau of Customs and Border Protection and USDA APHIS should instead penalize all importers whose wood packaging does not comply with the regulations.
• The Bureau of Customs and Border Protection should incorporate the wood packaging requirements into its “Customs-Trade Partnership Against Terrorism” (C-TPAT) program .
• USDA APHIS should re-examine the economic pros and cons of requiring importers to switch to packaging made from materials other than wooden boards. The new review should incorporate the high economic and ecological costs imposed by insects introduced via the wood packaging pathway.
• The President’s Office of Management and Budget should allow APHIS to finalize regulations – proposed in 5 years ago! – that would apply the same treatment requirements to wood packaging used in trade between the US and Canada. (Canada has been ready to adopt this measure for several years.)
• Importer’ contracts with suppliers routinely specify penalties for delivery delays; the contracts should be amended to add penalties for noncompliant wood packaging.
• A decade ago, USDA APHIS funded research which developed an ingenious method for detecting mobile pests inside a container. It was an LED light attached to a sticky trap. Placed inside a container, the light attracted snails, insects and possibly other living organisms. The whole mechanism was attached to a mailing container that could be pre-addressed for sending to a lab that could identify the pests. Why was this tool never implemented?

Posted by Faith Campbell

Alarming Genetic Variability Appears in SOD in Oregon & – as of 2020 – in California

Oregon authorities have announced that a dying tanoak detected by an aerial survey in the quarantine zone in Curry County, Oregon has proved to be in the EU1 clonal lineage. This is the first report of the EU1 lineage in North American forests. All other isolates of the causative pathogen Phytophthora ramorum in North American forests are the NA1 lineage. [See below for a discussion of P. ramorum clonal lineages.]

Dying tanoak (in California). Photo by F.T. Campbell
The infected tree is near a small private nursery that had been reported infested with the EU1 lineage of P. ramorum in 2012. The nursery carried out the APHIS-mandated Confirmed Nursery Protocol, then closed. Genetic testing suggests this nursery is the probable source population for the EU1infestation of the tree.This incident conveys several lessons:

Discovery of the EU1 lineage of P. ramorum in the forest appears to confirm that nursery infestations can infect plants in the forest.
The importance of genetic testing of samples from every infestation to determine which clonal lineage is present.

The discovery has troubling implications: The EU1 lineage consistently is a more aggressive pathogen than the NA1 clonal lineage already present in forests in California and Oregon. The EU1 lineage kills several types of conifer trees in Europe, including western hemlock (Tsuga heterophylla).
Furthermore, the EU1 lineage is of the opposite mating type as NA1, creating at least a small potential for sexual reproduction and increased variability in the pathogen population. (Sexual reproduction in P. ramorum can only occur when opposite mating types meet; in the absence if opposite mating types, all reproduction is clonal.)
The Oregon Department of Forestry is attempting to eradicate this small infestation. Host plants on the infested site have been cut and piled and will be burned as soon as wildfire risk abates. (Burning of other, lower priority sites has been delayed by inadequate funding). Authorities will also continue intensive surveys and will monitor soil and vegetation before and after treatment. Some funding for this work will come from the USDA Forest Service Forest Health Protection program and USDA-APHIS.

LINEAGES:
The Phytophthora ramorum pathogen is known to have four separate genetic lineages. The NA1lineage is the form of the pathogen established in forests of California and Oregon. This lineage is also the most common lineage in U.S. nurseries. However, two other genetic lineages are also found in U.S. nurseries: NA2 and EU1 (Coats and Chastagener 2009; Mascheretti et al. 2009). Indeed, NA2 was the most common lineage in Canadian nurseries (Goss et al. 2011).
The EU1 strain is widespread in European nurseries and in tree plantations and wild heathlands of southwest England, Wales, parts of Scotland, and Ireland. In 2012, a new, fourth strain was detected in Northern Ireland and a small area in southwest Scotland. This strain is called EU2.This strain is attacking larch, beech, fir, and hemlock trees at these sites (California Oak Mortality newsletter 2015).

Most EU1 and all EU2 type isolates belong to the A1 mating type, whereas the two North American strains belong primarily to the A2 mating type (Hansen et al. 2003). While P. ramorum apparently reproduces sexually only rarely, the presence of both mating types – in nurseries and especially in forests – does increase the possibility that sexual reproduction will occur. Sexual reproduction would allow the pathogen to evolve and perhaps become more aggressive.

NEW SITUATION:

The EU1 strain was detected in forest trees in Del Norte County, California in autumn 2020. This detection was both the first officially confirmed detection of P. ramorum in Del Norte County and the first detection of the EU1 strain in forest trees in California. The source is unclear. The nearest infestation is 12 miles away in Curry County, Oregon; those trees are infected with the NA1 strain. The nearest known EU1 infestation is about 35 miles away. The site of the California EU1 infestation has minimal California bay laurel (Umbellularia californica). This detection has led to designation of Del Norte County as officially infested; it becomes the 16^th California county so designated. [Information from the California Oak Mortality Task Force newsletter for December 2020, available here.]

SOURCES

California Oak Mortality Task Force newsletter [http://www.suddenoakdeath.org/news-and-events/newsletter-archive/ ] April 2015.

Coats, K. and G. Chastagener. 2009. Understanding the mechanisms behind detections of Phytophthora ramorum in Washington State nurseries and streams utilizing microsatellite genotype information. Fourth Sudden Oak Death Science Symposium, June 15-18, Santa Cruz, CA.

Goss, E.M., M. Larsen, A. Vercauteren, S. Werres, K. Heungens, and N.J. Grünwald. 2011. Phytophthora ramorum in Canada: Evidence for Migration Within North America and from Europe. Phytopathology. January 2011, Volume 101, Number 1. Pages 166-171

Hansen, E.M., P.W. Reeser, W. Sutton, L.M. Winton, and N. Osterbauer. 2003. First Report of A1 Mating Type of Phytophthora ramorum in North America. Plant Disease, October 2003, Volume 87, Number 10. Page 1267.

Mascheretti, S., P.J.P. Croucher, M. Kozanitas, L. Baker, M. Garbelotto.2009.Genetic epidemiology of the Sudden Oak Death pathogen Phytophthora ramorum in Calif.Molecular Ecology 18: 4577-4590.

Posted by Faith T. Campbell

SOD in the East

At present, sudden oak death (SOD) is killing trees and shrubs in forests along the Pacific coast from far southern Oregon to Monterey County in California – a stretch of more than 400 miles.

However, numerous tree and shrub species native to forests in the East also are vulnerable to the pathogen. These include several oak trees (northern red, chestnut, white, and pin oaks), sugar maple, black walnut; and such shrubs as mountain laurel and rhododendrons.

While no infestations of SOD have been found in the wild in the East, the pathogen is already present in some nurseries and continues to be transported to disease-free parts of the Southeast in shipments of nursery plants – as described in my previous blog.

Nine eastern states monitor streams to detect the pathogen in water. These states are AL, FL, GA, MS, NC, NY, PA, SC, & TX. As of 2013, six states had detected the pathogen in a total of 11 streams and ponds; all were outside nurseries that had previously had infested plants. These positive streams were distributed as follows: AL-4; FL-1; GA-2; MS-1; NC-1; TX-2.

In 2014, only four states (instead of six) detected the SOD pathogen in at least one stream: AL-4; FL-1; MS-2; and NC-2. Two of these streams were new – one each in AL and FL.

One of the AL detections is in a stream associated with a nursery that had not previously been determined to have infested plants. Authorities plans to sample vegetation near this stream. In the past, once a stream had tested positive, it remained positive in all subsequent years. However, the testing methods are not perfect so some variation in findings can be expected.

Infested plants were found growing in the ground (outside a nursery) at three sites: one each at homes in CT and MA; and a commercial business site in LA. These searches were undertaken because officials knew that these residents or businesses had bought plants from an infested nursery in earlier years.

As noted in my previous blog, SOD has been detected in eight nurseries in the East: ME-1, NY-2, TX-1, VA-4). The TX nursery became infested by plants received from a California nursery. I am very concerned about the presence of the pathogen in four Virginia nurseries, because the Commonwealth falls in the geographic region thought to be most vulnerable to the pathogen [see risk maps in the SOD writeup at http://www.dontmovefirewood.org/gallery-of-pests or in Chapter 5 of Fading Forests III.

Is the Government Preventing Movement of Sudden Oak Death (SOD) to Vulnerable Areas in the East?

Are the Rules Working?

APHIS adopted a new approach to regulating interstate trade in SOD hosts in early 2014. One year later, spring 2015, it is too soon to provide a thorough evaluation of whether this approach is effective in ending the risk that the disease will be moved to new areas on nursery plants. But some problems have already shown up, suggesting that the approach has serious weaknesses and will not succeed as intended.

1) APHIS’s new program is unlikely to find either new or cryptic infestations quickly.

When APHIS put its program into force in March 2014, 23 nurseries in California, Oregon, and Washington that had tested positive for the pathogen in the previous three years signed up to participate in the program – thus complying with the requirements for continuing to ship SOD host plants interstate. By the end of 2014, three of those nurseries had dropped out – so they can now ship plants only to retailers/purchasers within their states. A fourth nursery was expelled from the program because of its continuing inability to eradicate the pathogen from its premises. This nursery is no longer allowed to ship SOD hosts out of state.

At the same time, two additional nurseries joined the program. So as of the end of 2014, 21 nurseries were participating. Seven participating nurseries are in California; all have tested free of the pathogen in spring 2015. Ten participating nurseries are in Oregon; four of these nurseries tested positive for the pathogen in spring 2015.

Many more nurseries in the three states that had been tested for the pathogen over the past three years and found not to be infested are now allowed to ship plants interstate without being subject to the new APHIS requirements. (For example, in 2013 California tested plants in 1,575 nurseries; only one positive nursery was found.) The issue now is whether these nurseries are truly clean of the pathogen, and will remain so. Since the SOD pathogen was extremely difficult to detect in plants (the system relied upon before 2014), I am concerned that nurseries that tested “clean” before 2014 might have harbored a cryptic infestation that escaped detection.

Such cryptic pre-existing infestations – and any new infestation that establishes in a nursery not currently subject to the regulation due to a previous infestation – will probably escape detection for months because, under the current APHIS program, the presence of SOD in these nurseries will be detected only under one of the following conditions:

The nursery owner reports symptoms of infestation;
The state detects symptomatic plants during a routine state inspection; or
The nursery is identified as the source of infested plants purchased by someone (this is called a trace-back investigation).

Some nurseries that had been shipping SOD host plants interstate under the previous APHIS regulations chose to stop shipping host plants interstate and so did not agree to abide by the new requirements. I know that five Oregon nurseries opted out; APHIS has not told me how many nurseries in California and Washington also opted out.

picture of infested rhododendron plant;

courtesy of Jennifer Parke, Oregon State University

The risk that nursery plants will spread SOD continues.

How large is this risk? One measure is how many nurseries are infested with the disease – either through a new introduction or as a result of an earlier infestation that was not detected.

During 2014, state inspectors detected the SOD pathogen in 19 nurseries – almost the same number as in 2013, and slightly more than half the number in 2012. (For a discussion of the SOD pathogen in nurseries in recent years, read Chapter V in Fading Forests III. Eleven of these nurseries were in the three west-coast states that have been regulated most tightly in the past (CA-1, OR-8, WA-2); eight nurseries were in other parts of the country (ME-1, NY-2, TX-1, and VA-4).

Fourteen of the 19 nurseries had tested positive for the pathogen during the previous three years. Consequently, they had been subject to the new regulation from its implementation.

However, two nurseries had tested positive before 2011, but not during the key 2011-2013 period. Under the terms of the 2014 regulation, these nurseries were not subject to APHIS’s new regulation and they continued to ship plants. This raises concerns about whether infestations in some nurseries might not be detected under the new regime before they ship plants to disease-free areas.

Eight of the 19 infested nurseries were interstate shippers (CA-1; OR-4; WA-1; TX-1; VA-1). Six had shipped plants in the previous six months.

Five of these infested interstate shippers stayed in the new APHIS program, carried out Critical Control Point Assessments, and adopted specific mitigation actions that were approved by APHIS and state officials. They continue to ship SOD host plants interstate.

Four of the eight infested nurseries left the program, either voluntarily or by compulsion. Nurseries not in the APHIS program may now ship SOD host plants only to destinations within their states; they are subject to regulation by their state agencies (usually, departments of agriculture).

Eleven of the nurseries detected to be infested by the SOD pathogen in 2014 shipped only to retailers within their own states; these nurseries are regulated by the appropriate state rather than by APHIS.

Strengths and Weaknesses of the New Regime

So, what do I see as the strengths of the new regulatory regime? Most important, inspectors test the soil, water, and pots, not just symptomatic plants. This approach, recommended by scientists for years before APHIS adopted it, is paying off: inspections detected the pathogen twice in potting media, six times in a nursery’s soil, and 15 times in water on nursery premises.

The greatest weakness is the three-year cutoff for including nurseries in the APHIS program; as demonstrated already, nurseries can be clean for three years and then again be found to be infested. It has always been difficult to determine whether these “repeat” nurseries were infested all along, but somehow escaped detection; or have become infested through a new introduction of the pathogen.

Questions also arise because of the reliance on state regulation of nurseries shipping only within the state. Some state agencies appear to be much more aggressive than others in searching for symptoms of infestation and requiring cleanup.

Another possible problem is that the regulatory inspection effort focuses on five genera — Camellia, Kalmia, Pieris, Rhododendron, and Viburnum — but plants in other genera are also hosts. During 2014, detections were made on the following genera that are not among the “high-risk” hosts — Gaultheria, Prunus, Syringa and Vaccinium; and seven new host species were detected in the forest or in nurseries. One of these apparently new hosts, Vinca, is a widely planted ground cover (“periwinkle”) shipped in flats of often sad-looking rooted cuttings.

One good sign is that the nursery trade and state agricultural agencies are seeking ways to decrease the movement of plant pests via the nursery trade. Examples of such pest movement are not limited to SOD or other tree-killing pests; for example, boxwood blight was first detected in the United States in 2011; by 2013 it was known to be in nine eastern states and Oregon.

The nursery trade (through their trade associations, AmericanHort and the Society of American Florists), state agencies, and APHIS have developed a voluntary program called Systems Approach to Nursery Certification, or SANC. The collaborating organizations devoted several years to developing an agreed-upon set of standards and procedures aimed at making their facilities as free of disease and pests as possible. Now they are testing whether the program works in practice. Eight plant growers from across the country – and the appropriate state agencies – have agreed to:

Assess the facility for situations and practices that create a risk of pest infestation;
Identify best management practices that will mitigate those risks; and
Develop new facility-management manuals that apply those practices.

The SANC managers expect the pilot program to take 3 years (2018).

The principal sources for the information in this blog are the monthly newsletters prepared by the California Oak Mortality Task Force (COMTF), found at http://www.suddenoakdeath.org/ and the USDA APHIS program updates found at http://www.aphis.usda.gov/wps/portal/aphis/ourfocus/planthealth/sa_domestic_pests_and_diseases/sa_pests_and_diseases/sa_plant_disease/sa_pram/ct_phytophthora_ramorum_sudden_oak_death/