Category: forest pathogens

Sudden Oak Death – Bad News All Around

SOD in California;
photo by Joseph O’Brien. courtesy of Bugwood

We know that the international trade in living plants is a major pathway by which tree-killing pathogens are being spread – some of them again and again. According to Grünwald et al. (2019), Phytophthora ramorum, the pathogen that causes Sudden Oak Death (SOD), has been introduced to North America and Europe – probably from Asia – at least five times. One lineage or genetic strain – EU1 – has been established on both continents (strains explained here). There is strong evidence of two separate introductions to Oregon, at least 12 to California.

Jung et al. 2015 state definitively that the international movement of infested nursery stock and planting of reforestation stock from infested nurseries have been the main pathway of introduction and establishment of Phytophthora species in European forests.  

Clive Btasier in Vietnam
photo from UK Forest Research

Jung et al. 2020 have demonstrated that P. ramorum probably originated in Vietnam.  This region appears to be a center of diversity for Phytophtoras and other Oomycetes: baiting of soil and streams resulted in the detection of 13 described species, five informally designated taxa, and 21 previously unknown taxa of Phytophthoras plus at least 15 species in other genera. Noting the risk associated with any trade in plants from this region, the authors re-iterated past appeals that the international phytosanitary system replace the “outdated and scientifically flawed species-by-species regulation approach based on random visual inspections for symptoms of described pests and pathogens” by instituting “a sophisticated pathway regulation approach using pathway risk analyses, risk-based inspection regimes and molecular high-throughput detection tools.”

Pathogen’s Spread Proves U.S. Domestic Regulations Governing Nursery Trade Are Inadequate

Last year I blogged about the most recent spread of Phytophthora ramorum through the nursery trade.  As of now, we know that shipments of potentially infected plants had been sent to 18 states. Infected stock had been detected in nurseries in seven of these (Iowa, Illinois, Indiana, Kansas, Missouri, Nebraska, Oklahoma) plus the source state, Washington [COMTF Newsletter August 2019].

Since then, I learned [COMTF newsletter for December 2019]   that these plants were infected by the NA2 strain of the pathogen. This is the first time that this strain has been shipped to states outside the West Coast. It is unclear what the impact will be if – as is likely – infested plants are still extant in purchasers’ yards. Both the NA1 strain (the strain established in most infested forests of California and Oregon) and the NA2 strain belong primarily to the A2 mating type, so the potential spread of NA2 lineages might not exacerbate the probability of sexual reproduction of the pathogen.

I applaud agencies’ funding of genetic studies to determine the lineage of the pathogen involved. It not only helps narrow the possible sources of infected plants, but also could be important in determining risk and management options.

I have long criticized USDA’s P. ramorum regulatory program – see Fading Forests III and my blogs discussing the most recent revisions to the regulations here and here. I believe that both the earlier regulations and the revisions finalized last May provide inadequate protection for America’s forests. 

The updated regulations do take a couple of important positive steps. First, APHIS is now authorized to sample water, soil, pots, etc. – and to act when it finds evidence of the pathogen’s presence. APHIS also now mandated nurseries found to be infested to carry out a “critical control point analysis” to determine practices which facilitated establishment and persistence of P. ramorum.

However, these improvements are severely undermined by continuing the five-year-old practice of limiting close scrutiny to only those nurseries that tested positive for the pathogen in the recent past. The flaw in this approach was starkly demonstrated by the pathogen’s spread in 2019. The Washington State nursery that was the source of the infected plants had not previously been positive, so it was under routine nursery regulation, not the more stringent federal P. ramorum program.

Too often various iterations of the regulations have allowed infected plants to be shipped. Between 2003 and 2011, a total of 464 nurseries located in 27 states tested positive for the pathogen, the majority as a result of shipments traced from infested wholesalers (Campbell). The number of nurseries found to have infected plants has since declined, but not dropped to zero. These include 34 nurseries in 2010 (COMTF February 2011 newsletter), 21 in 2012, and 17 in 2013 (Pfister). During 2014, state inspectors detected the SOD pathogen in 19 nurseries – 11 in the three west-coast states and eight in other parts of the country (Maine-1, New York-2, Texas-1, and Virginia-4) COMTF newsletter December 2014). Despite the continuing presence of the pathogen in the nursery trade, APHIS formalized existing practices that narrowed the regulators’ focus to only those nurseries with a history of pathogen presence. This approach has been shown to fail – we need APHIS and the states to find a way to broaden their scrutiny.

The most immediate impact of the continuing presence of P. ramorum in the nursery trade is the burden borne by eastern states’ departments of agriculture. They are obligated to seek out in-state nurseries that might have received infected plants; inspect those plants; and destroy the infected plants, test nearby plants, and try to find and retrieve plants that had been sold. The heaviest, and most direct, burden is borne by the receiving nurseries. Anger about bearing this burden for 15 years doubtless prompted the National Plant Board to adopt a tart resolution calling on APHIS to carry out a review of its communications to the states during the 2019 incident. The NPB also questioned whether current program processes and guidance are effective in preventing spread of this pathogen. 

Unfortunately, the NPB had not commented formally on the rule change when it was proposed.

The states’ frustration is exacerbated by the fact that under the Plant Protection Act, when APHIS takes a regulatory action it prevents states from adopting more stringent regulations. While the law allows for exceptions if the state can demonstrate a special need, none of the five applications for an exemption pertaining to P. ramorum was approved (Porter and Robertson 2011). I have been unable to find evidence of petitions submitted in the nine years since 2011.

In Case You Needed A Reminder: P. ramorum is a Dangerous Pathogen – as Proved by the Situation in the West states and Abroad

Continuing Intensification of the Already Bad Infestations in the West

tanoak mortality in Big Sur
photo courtesy of Matteo Garbelotto, UC Berkeley

As of 2014 (see COMTF November 2018 newsletter available here), perhaps 50 million trees had been killed by P. ramorum in California and Oregon. The vast majority were tanoaks (Notholithocarpus densiflorus)  – an ecologically important tree. 

Since 2014, the disease has intensified and spread in response to recent wet winters. In 2016 (see COMTF

November 2016 newsletter here) disease was detected for the first time in a fifteenth California county and new outbreaks or more severe infestations were recorded in seven other counties.  In 2019, SOD was detected in the sixteenth county. Tanoak mortality in California increased by more than 1.6 million trees across 106,000 acres in 2018.

Perhaps more disturbing, the disease has also intensified on the eastern side of San Francisco Bay – an area thought to be less vulnerable because it is drier and where there are fewer of the principal sporulation host, California bay laurel (see COMTF March 2017 newsletter here).

A second disturbing event is the detection in Oregon forests of the EU1 strain of Phytophthora ramorum. The August 2015 detection was the first instance of this strain being detected in a forest in North America. Oregon authorities prioritized removing EU1-infected trees and treating (burning) the immediate area, which had expanded to more than 355 acres – all within the quarantine area in Curry County. The legislature provided $2.3 million for SOD treatments for 2017-2019 (Presentation by Chris Benemann of Oregon Department of Agriculture to the Continental Dialogue on Non-Native Forest Insects and Diseases; reported here).

The EU1 lineage is a different mating type than the NA1 lineage already established in Oregon. Scientists should study P. ramorum populations in Vietnam and Japan, where both mating types are present, to determine whether they are reproducing sexually. There is also the risk that the EU1 lineage might be more aggressive on conifers – as it has been in the United Kingdom (Grünwald et al. 2019).

The EU1 infestation was introduced to the forest from a nursery. The nursery had carried out the APHIS-mandated Confirmed Nursery Protocol, then closed.  I ask, what does this apparent transmission from nursery to forest say about the risk of transmission? Does it raise questions about the efficacy of the confirmed nursery protocol to clean up the area? Remember that a pond at the botanical garden in Kitsap, Washington has repeatedly tested positive, despite several applications of the clean-up protocols.

(For a discussion of the implications of mixing the various strains of P. ramorum, visit here)

These disasters remind us how sad it is that California and federal officials did not adopt aggressive management efforts aimed at slowing the pathogen’s spread at an early stage of  the epidemic. Experts on modeling the epidemiology of plant disease concluded three years ago that the sudden oak death epidemic in California could have been slowed considerably if aggressive and well-funded management actions had started in 2002 (Cunniffe, Cobb, Meentemeyer, Rizzo, and Gilligan 2016).

The Oregon Department of Forestry commissioned a study of the economic impact of the P. ramorum infestation that found few economic impacts to date, but potentially significant impacts in the future. It also noted potential harms to tribal cultural values and the “existence value” of tanoak-dominated forests and associated obligate species.

Situation Abroad

The situation in Europe is even worse than in North America. Two strains of P. ramorum are widespread in European nurseries and in tree plantations and wild heathlands of western the United Kingdom and Ireland. and here and here.  Jung et al. 2015 found 56 Phytophthora taxa in 66% of 2,525 forest and landscape planting sites across Europe that were probably introduced to those sites via nursery plantings.

larch plantation in UK killed by P. ramorum
photo from UK Forest Research

In Australia, Phytophthora dieback has infected more than one million hectares in Western Australia. More than 40% of the native plant species of the region are vulnerable to the causal agent, P. cinnamomi

 and here.  

Barber et al. 2013 reported 9 species of Phytophthora associated with a wide variety of host species in urban streetscapes, parks, gardens, and remnant native vegetation in urban settings in Western Australia. Phytophthora species were recovered from 30% of sampled sites.

In New Zealand, the endemic – and huge, long-lived – kauri tree (Agathis australis) is also suffering severe impacts from Phytophtoras and other pathogens (Bradshaw et al. 2020)

See the IUFRO Working Party 7.02.09 ‘Phytophthora Diseases of Forest Trees’ global overview (Jung et al. 2018), which covers 13 outbreaks of Phytophthora-caused disease in forests and natural ecosystems of Europe, Australia and the Americas.

The situation in the Eastern United States is Unclear

After 15 years of the nursery trade carrying P. ramorum to nurseries – and possibly yards and other plantings – in states east of the 100th Meridian, what is the risk that these forests will become infested? No one knows. We do known that the pathogen has been detected from 11 streams in six eastern states – four in Alabama; one in Florida; two in Georgia; one in Mississippi; one in North Carolina; and two in Texas. P. ramorum has been found multiple times in eight of these streams – two steams in Alabama, one each in Mississippi and North Carolina (see COMTF April 2019 newsletter available here). While established vegetative infections have not been detected, the question remains: how is the pathogen persisting? Scientists agree that P. ramorum cannot persist in the water; it must be established on some plant parts (roots?) or in the soil. Still, Grünwald et al. (2019) report that there is little evidence of plant infections resulting from stream splash in Oregon.

Unfortunately, fewer states are participating in the stream surveys – which are operated by the USDA Forest Service. In 2010, 14 states participated; in 2018, only seven (Alabama, Georgia, Mississippi, North Carolina, Pennsylvania, South Carolina, and Texas). Florida and Tennessee recently dropped out. The number of streams surveyed annually also has dropped – from 95 at the highest to only 47 in 2018 (see COMTF April 2019 newsletter available here). This reduced scrutiny makes it less likely that any infestation on plants will be detected. Risk maps (reproduced in Chapter 5 of Fading Forests III here) developed over more than a decade indicate that forests in the southern Appalachians and Ozarks are vulnerable to SOD.

Risks to other plants

The risk from Phytophthoras is not just P. ramorum and trees! Swiecki et al. 2018 report a large and increasingly diverse suite of introduced Phytophthora species pose an ever greater threat to both urban and non-urban plant communities in California. These threats are linked to planting of nursery stock. See also the information posted here.

Jung et al. 2018 cite numerous other authors’ findings of multiple Phytophthoras in Oregon and. California nurseries as well as in nurseries in various eastern states.

Nor is Phytophthoras the only pathogenic genus to pose a serious risk to America’s trees. I remind you of the fungus Fusarium euwallacea associated with the Kuroshio and polyphagous shot hole borers, which is known to kill at least 18 species of native plants in California and additional species in South Africa.   The laurel wilt fungus kills many trees and shrubs in the Lauraceae family. ‘Ohi‘a or myrtle rust kills several shrubs native to Hawai`i and threatens a wide range of plants in the Myrtaceae family in Australia and New Zealand; rapid ‘ohi‘a death fungi (Ceratocystis huliohia and Ceratocystis lukuohia)  [All described here] are killing the most widespread tree on the Hawaiian Islands.

Solutions – complete & implement modernized international and domestic phytosanitary regulations

Clearly, standard phytosanitary practice of regulating pests known to pose a threat does not work when many – if not most – of the damaging pests are unknown to science until introduced to a naïve ecosystem where they start causing noticeable levels of damage. We need a more proactive approach – as has long been advocated by forest pathologists, including Clive Brasier 2008 and later, Santini et al. 2013, Jung et al. 2016, Eschen et al. 2017.

National and international phytosanitary agencies have taken some steps toward adopting policies and programs that all hope will be more effective in preventing the continued spread of these highly damaging tree-killing pests. First, APHIS has had authority since 2011 – through the Not Authorized for Importation Pending Pest Risk Assessment (NAPPRA) program — to prohibit temporarily imports of plants suspected of transporting known damaging pathogens until the agency has conducted a pest risk analysis. However, utilization has lagged: only three sets of species have been proposed for listing in NAPPRA in the eight and a half years since the program was instituted in 2011. The third list of proposed species is currently open for public comment.

Another weakness is that the program still focuses on organisms known to pose a risk.

Second, in 2018 APHIS completed a decades-long effort to revise its plant import regulations (the “Q-37” regulations). APHIS now has authority to require foreign suppliers of living plants to carry out “hazard analysis and critical control point” programs and adopt integrated pest management strategies to ensure that the plants are pest-free during production and transport.

However, implementation of this new authority depends on APHIS negotiating agreements with individual countries that would govern specific types of plants exported to the U.S. APHIS has not yet announced completion of any programs under this authority. Nor is it clear which taxa or countries APHIS will prioritize.

APHIS’ action was anticipated by the international plant health community. In 2012, member states in the International Plant Protection Convention adopted International Standard for Phytosanitary Measure 36 (ISPM#36)  The standard sets up a two-level system of integrated measures, which are to be applied depending on the pest risk identified through pest risk analysis or a similar process. The “general” integrated measures are widely applicable to all imported plants for planting. The second level includes additional elements designed to address higher pest-risk situations that have been identified through pest risk analysis or other similar processes. 

However, the preponderance of international efforts to protect plant health continues to rely on visual inspections that look for species on a list of those known to be harmful. Yet we know that most damaging Phytophthoras were unknown before their introduction to naïve ecosystems.

Furthermore, use of fungicides and fungistatic chemicals – that mask infections but do not kill that pathogen – is still allowed before shipment.

(For more complete analyses of the Q-37 revision and ISPM#36, see chapters five and four, respectively, of Fading Forests III.)

The nursery industry is working with state regulators and APHIS to develop a voluntary program utilizing  integrated measures – the Systems Approach to Nursery Certification (SANC) program. https://sanc.nationalplantboard.org/

SOURCES

Bradshaw et al. 2020. Phytophthora agathidicida: research progress, cultural perspectives and knowledge gaps in the control and management of kauri dieback in New Zealand. Plant Pathology (2020) 69, 3–16 Doi: 10.1111/ppa.13104

Brasier CM. 2008. The biosecurity threat to the UK and global environment from international trade in plants. Plant Pathology 57: 792–808.

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 lateralis

Fungal Biology. Volume 116, Issue 12, December 2012, Pages 1232–1249

Campbell, F.T. Calculation by F.T. Campbell from tables in U.S. Department of Agriculture, Animal and Plant Health Inspection Service – National Plant Board.  2011.  Phytophthora ramorum Regulatory Working Group Reports.  January 2011.

Cunniffe, N.J., R.C. Cobb, R.K. Meentemeyer, D.M. Rizzo, and C.A. Gilligan. Modeling when, where, and how to manage a forest epidemic, motivated by SOD in Calif. PNAS, May 2016 DOI: 10.1073/pnas.1602153113

Grünwald, N.J., J.M. LeBoldus, and R.C. Hamelin. 2019. Ecology and Evolution of the Sudden Oak Death Pathogen Phytophthora ramorum. Annual Review of Phytopathology date? #?

Jung T, Orlikowski  L, Henricot B, et al. 2016. Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora diseases. Forest Pathology 46: 134–163.

Jung, T., A. Pérez-Sierra, A. Durán, M. Horta Jung, Y. Balci, B. Scanu. 2018. Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands. Persoonia 40, 2018: 182–220   Open Access!

Jung, T. et al. 2015. Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora disease. Forest Pathology. November 2015; available from Resource Gate

Jung, T., B. Scanu, C.M. Brasier, J. Webber, I. Milenkovic, T. Corcobado, M. Tomšovský, M. Pánek, J. Bakonyi, C. Maia, A. Baccová, M. Raco, H. Rees, A. Pérez-Sierra & M. Horta Jung. 2020. A Survey in Natural Forest Ecosystems of Vietnam Reveals High Diversity of both New and Described Phytophthora Taxa including P. ramorum. Forests, 2020, 11, 93 https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.mdpi.com%2F1999-4907%2F11%2F1%2F93%2Fpdf&data=02%7C01%7C%7Cfcd843919a3348a4a56108d7974039ab%7Ced5b36e701ee4ebc867ee03cfa0d4697%7C0%7C1%7C637144174418121741&sdata=WayrZsxp3P9Kj0h1aDPZnzu4yjDGA2ZEuH9NZITFQF4%3D&reserved=

Knaus, B.J., V.J. Fieland, N.J. Grunwald. 2015. Diversity of Foliar Phytophthora  Species on Rhododendron in Oregon Nurseries. Plant Disease Vol 99, No. 10 326 – 1332

Pfister, S. USDA APHIS. Presentation to the National Plant Board, August 2013

Porter, R.D. and N.C. Robertson. 2011. Tracking Implementation of the Special Need Request Process Under the Plant Protection Act. Environmental Law Reporter. 41.

Santini A, Ghelardini L, De Pace C, et al. 2013. Biogeographic patterns and determinants of invasion by alien forest pathogens in Europe. New Phytologist 197: 238–250.

Swiecki, T.J., E.A. Bernhardt, and S.J. Frankel. 2018. Phytophthora root disease and the need for clean nursery stock in urban forests: Part 1 Phytophthora invasions in the urban forest & beyond. Western Arborist Fall 2018

Tsao PH. 1990. Why many Phytophthora root rots and crown rots of tree and horticultural crops remain undetected

Sudden Oak Death update

P. ramorum-infected rhododendron plants
Indiana Department of Natural Resources

As you may remember, in June and July I blogged about a troubling outbreak of sudden oak death pathogen Phytophtora ramorum in the nursery trade. The discovery was made by Indiana authorities, who carefully inspected plants being sold in the state. They discovered that rhododendron plants imported from an Oklahoma wholesaler included infected plants.

By the end of May, Indiana state inspectors had destroyed more than 1,500 rhododendrons and prohibited sale of another 1,500 plants  pending determination of their health. [source: Indianapolis Star 29 May, 2019]  Over the next months, APHIS determined that more than 50 rhododendron plants found in Indiana nurseries had been infected [California Oak Mortality Task Force Newsletter August 2019 ].

In the spring and summer, APHIS and state authorities alerted 28 states that they might have received plants from the suspect sources – the suppliers of the Oklahoma wholesaler — one nursery in Washington State and two nurseries from Canada. In the end, APHIS determined that plants exposed to the pathogen had been sent to 18 states – Alabama, Arkansas, Iowa, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Nebraska, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Virginia, and West Virginia. As of late July, P. ramorum-positive nursery stock had been detected in nurseries in seven of these (Iowa, Illinois. Indiana, Kansas, Missouri, Nebraska, Oklahoma) plus  Washington [California Oak Mortality Task Force Newsletter August 2019].

As I pointed out in the earlier blog, this is just the latest of several occasions since 2004 in which infected plants have been widely distributed by the nursery trade, despite federal and state regulations. Also, at the time of this outbreak, APHIS had just formalized several steps relaxing the regulations that had been implemented through Federal Orders adopted in recent years. (See the earlier blog for details.)

APHIS actions

I wonder at APHIS’ delay in explaining to stakeholders the situation– and what it is doing about it!  APHIS provided minimal information to me – by email rather than a public announcement; this email came a month after Indiana announced detection of the pathogen to the public (as reported in my blog).  APHIS issued an official notice even later, in mid-July [California Oak Mortality Task Force (COMTF) Newsletter August 2019]. Neither notice was timely, given the serious risks to both nursery and naturally growing plants from the pathogen.

It is now November and principal questions have not yet been answered. How did the inspection systems in Washington and British Columbia fail to detect the outbreaks before the plants were shipped? This lapse is especially worrisome because APHIS requires testing of soil and standing water, not just visual inspection of plants. Furthermore, rhododendrons are well known to be vulnerable to the pathogen and therefore are a specified focus of detection efforts!

The October COMTF newsletter includes a report by the Washington State Department of Agriculture that a nursery found positive in May will carry out a Critical Control Points (CCP) assessment. An “extensive fall certification survey” will also be conducted. Presumably, these efforts are aimed at determining how the outbreak occurred.

The Canadian Food Inspection Service (CFIA) described – briefly – its nationwide survey program. CFIA reported that one nursery was determined to be P. ramorum-positive in 2018, three in 2019. CFIA says that trace-forwards and trace-backs demonstrate that no Canadian nursery shipped infected plants to the U.S. in 2018 or 2019. So, apparently, none of the infected plants came from the Canadian nurseries.

I hope that Washington State and APHIS will soon determine the probable causes of the outbreak. APHIS should then promptly inform all stakeholders and engage them in developing improved programs and policies to minimize the likelihood that similar problems will occur again.

Phytosanitary officials from the states are apparently also seeking additional information from APHIS about what went wrong and how the agency plans to fix the problems. See the resolution adopted by the National Plant Board here

California Action

A much more positive development is that the California Department of Food and Agriculture (CDFA) has introduced a Voluntary P. ramorum Pre-Quarantine Program. This is a voluntary inspection program specifically for nurseries in California counties that are not currently regulated for the pathogen – but that might be put under regulation in the future. Inspections and sampling will be administered by county regulatory officials and samples will be processed by the CDFA Plant Pest Diagnostics Center. If P. ramorum is detected at a participating nursery, the PQP nursery may become a federally regulated establishment.

Broader Implications

As I pointed out in Fading Forests III, APHIS and the states have struggled to prevent spread of tree-killing pests once they have established in the country. Even regulated pests – such as Phytophthora ramorum and the emerald ash borer — have escaped the regulations. APHIS and/or the states have chosen not to engage on other pests, such as redbay ambrosia beetle and laurel wilt disease and the polyphagous and Kuroshio shot hole borers and associated Fusarium fungus. In other cases, some states have acted – and asked APHIS to not get involved – e.g., thousand cankers disease of walnut. This situation heightens the risk to our urban, rural, and wildland forests. Americans need a hard-nosed discussion of how we can improve coordinated efforts to prevent pests’ spread.

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.

Phytophthora ramorum spreads in nursery trade – again!

Rhodendron infected by P. ramorum
photo by Jennifer Parke, Oregon State University

It might be déjà vu all over again.

Fifteen years ago, in the spring of 2004, officials discovered that the disease called “sudden oak death” or “ramorum blight” was present on camellias at a large California nursery that shipped $30 million worth of plants interstate on an annual basis. The nursery was in southern California, far from the wetter areas of northern California where the disease is established in the wild and where regulatory efforts were focused. By the end of 2004, 176 nurseries in 21 states had received infected plants, 125 of which were linked to the California supplier.  APHIS and the affected states and nurseries had to spend millions to find and destroy infected plants and conduct intensive surveys to try to ensure this situation was not repeated. 

APHIS had begun regulating P. ramorum in nurseries in northern California and Oregon in February 2002. These regulations went through several rounds of change after the 2004 outbreak – discussed in Chapter 5 of Fading Forests III, available here.

Beginning in 2014, APHIS issued two Federal orders that relaxed some of the regulatory requirements for nurseries.

Just this past May, APHIS completed the process of integrating these changes into its formal regulations. (See my blog from May and the text of the new regulations here.)  APHIS stated in replying to comments on the rulemaking that it was confident that the new regime provided sufficient protection.

Even as APHIS was finalizing this rule change, Indiana officials discovered that rhododendron plants imported into the state were infected with Phytophthora ramorum!!

Indiana authorities reported that potentially infested plants were received at more than 70 WalMart stores and 18 Rural King stores. By the end of May, state inspectors have destroyed more than 1,500 rhododendrons and have put another 1,500 other plants on hold [source: Indianapolis Star website 29 May, 2019]

Indiana authorities also said that the same source nurseries had shipped plants to nine other states – unnamed.

In mid-June – more than a month after Indiana’s initial detection [Indianapolis Star website 23 May] – APHIS issued a statement. In an email to me, Evelia Sosa, Assistant Director of Pest Management, reported that potentially infested plants from the original suppliers were sent to 18 states! These states are Alabama, Arkansas, Iowa, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Nebraska, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Virginia, and West Virginia. State officials Agriculture officials in these States are currently visiting nursery locations to sample plants received from the originating nurseries. Plants that test positive for P. ramorum will be destroyed. All plants that are within a 2 meter radius of an infected plant will also be destroyed. Host plants outside the 2 meter radius will be sampled intensively. Other hosts in the impacted facilities will be monitored for signs of the disease.

Homeowners who might have purchased infected plants are advised by APHIS to monitor them carefully for symptoms; a website is provided  — ironically (see below), it is the website of the California Oak Mortality Task Force!

Several of the states which received potentially infected plants have already been through this routine because infected plants were shipped to their nurseries in the 2004 – 2008 period. These include Alabama, North Carolina, and Texas. P. ramorum has been found multiple times in streams or ponds associated with the receiving nurseries (see my blog from May here)

There are several reasons for particular concern. First, the source nurseries were in Washington State and British Columbia. How did the inspection system fail to detect the outbreaks before the plants were shipped? Inspections now include testing of soil and standing water, not just visual inspection of plants. Second, at least some of the infected plants are rhododendrons – which are taxa well known to be vulnerable to the pathogen and the specified focus of detection efforts!

This would seem to verify concerns raised in its comments on the proposal (see the above website) by the California Oak Mortality Task Force, whose members have been studying and managing the outbreak for close to twenty years. COMTF said:

“The revised framework, in many ways, matches the rule structure present in 2004, when the pathogen was inadvertently, potentially shipped to over 1,200 nurseries in 39 states from a few nurseries in Southern California, Oregon and Washington. At that time, the APHIS P. ramorum regulation restricted shipments in the quarantine area, defined as the known infested counties in California and part of Curry Co., Oregon; however, the source nurseries were located in counties where P. ramorum was not present in wildlands. This revised framework does not adequately protect against the reality, that any nursery with host plants, anywhere, is a potential source for infested plants

How is APHIS going to respond – not just in leading efforts to detect and destroy infected plants but also to review its regulatory program? Why did APHIS wait so long to inform me – and presumably others in the public – about this most recent outbreak. (Although as of the time of posting, APHIS had not issued an announcement to the people registered on its stakeholder registry.)

It is not a surprise that APHIS is backing away from regulations. As I document in my blog here, the agency began some years ago to stress collaborative approaches rather than regulations.  But there are risks and costs associated with these decisions.

There are troubling situations applying to other forest pests that I hope to blog about soon.

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.

Recent Developments on Sudden Oak Death (Phytophthora ramorum)

tanoak killed by SOD; photo by F.T. Campbell

In recent months there have been several developments affecting efforts to manage the sudden oak death infestation in West Coast states and to prevent its spread to other parts of the country.

1) APHIS regulations

Most notably, APHIS has formalized revisions to its regulations governing nursery stock. This revision was proposed last June (see my blog about this here). The revisions largely implement changes to practices that APHIS had adopted in 4014 and 1015 through Federal Orders. The final regulation is posted here. The new regulation goes into effect on May 20th.

APHIS received only 10 comments (posted here) on the proposal – from researchers, State agriculture and conservation agencies, environmental advocacy groups, research foundations, and private citizens. I summarized points raised in their comments by CISP and others in an earlier blog.

APHIS responded to most of these comments by reiterating that it has been operating under the current program since 2014 and believes the existing testing protocols and conditions are sufficient to mitigate the risk. The measures to monitor nurseries for infections include testing soil and water, that is, they do not rely exclusively on visual inspection of the plants. This is a step forward. In response to comments by CISP and California Oak Mortality Task Force that all nurseries that grow host plants are a potential source of contamination, APHIS points out that it is not authorized to regulate nurseries that don’t ship plants interstate. This limitation is a serious problem arising from the underlying statute – the Plant Protection Act. APHIS said it would continue to monitor detection of the pathogen, and would reevaluate program protocols “should the need arise” – but it made no promise on how frequently it would  reevaluate the program.

APHIS did make some adjustments, based on comments. It agreed to one state’s request that it clarify the minimum number of samples that must be taken during annual inspection of nurseries that had not previously tested positive for the pathogen when those nurseries are located in counties that have SOD infestations in the environment. (Such counties are found only in California and Oregon.)

The agency also said it plans to restructure the list of host species so that it can be updated more quickly. APHIS plans to remove the lists from formal regulations (which require public notice and comment to amend) and post them on the APHIS website. APHIS also expects to merge the lists of proven and associated hosts into a single host list. However, these plans would, themselves, constitute rulemaking and require another public comment period.

APHIS also agreed to reinstate its quarterly program updates, beginning in April of 2019. I have not yet seen an alert telling me how to find the first such update, though.

2) P. ramorum in California and Washington

According to the most recent (April 2019) newsletter of the California Oak Mortality Task Force, tanoak (Notholithocarpus densiflorus) mortality in California attributed to Phytophthora ramorum increased by more than 1.6 million trees across 106,000 acres in 2018. The dead trees are concentrated west of the coastal range.

In the meantime, P. ramorum continues to be detected in nurseries shipping plants from West Coast nurseries. As of April, the California Department of Food and Agriculture had detected P. ramorum in nine nurseries – six from previous years, three new in 2019. (Sixty-four additional infected plants were found in one nursery that had been confirmed positive in an earlier year – raising questions in my mind about the efficacy of the Confirmed Nursery Protocol for eliminating the pathogen.)

As I noted in a previous blog, Washington is finding it difficult to eliminate P. ramorum from the soil of a botanical garden in Kitsap County. For the third time in less than a year, a pond that is downhill from previously “mitigated” sites has tested positive for P. ramorum.

I remind you that scientists do not believe that P. ramorum persists in water – it must be surviving on some plant tissue in both Washington and the Eastern states (see below).

3) P. ramorum in Oregon

The Oregon Department of Forestry (ODF) commissioned a study of the economic impact of Phytophthora ramorum in the state. The study found that to date, sudden oak death has caused minor impacts on the regional economy. There was  no impact on timber harvest, export or log prices or recreation or tourism revenues and only anecdotal reports of losses to real estate transaction values in some areas. Meantime, the state and several federal agencies are spending $1.5 million per year to try to contain the outbreak.

However, sudden oak death has the potential to cause harm to core values that elude economic quantification, particularly to tribal cultural values and the “existence value” of tanoak-dominated forests. SOD may be an existential threat to tanoak and associated obligate species (e.g., dusky-footed woodrats, Northern flying squirrels, and Allen’s chipmunks – which are important prey items for northern spotted owl, cougar, coyote, and Pacific fisher. More widespread wildlife — e.g., deer, elk, bear, Coho salmon, and a variety of bird species – might also be harmed.)

Immediate termination of the ODF treatment regime might lead to serious impacts due to more rapid expansion of sudden oak death into Coos County, Oregon. These could include Asian governments restricting timber and fiber exports from southwest Oregon and resulting loss of 1,200 jobs and forest products harvest tax. There might also be a collapse of residential property value and real estate transaction revenues. Finally, there might be a decline in recreation and tourism in affected areas. Maintaining the current treatment regime was expected to delay the spread of SOD north of the Rogue River until 2028, and prevent infestation of Coos County beyond 2038. Continued funding SOD treatments for a total cost of $30 million over the next 20 years could offset loss of 1,200 jobs by 2028 and $580 million in wages from 2028 to 2038.

The study authors note that other factors – such as major wildfires or trade wars – could render these impacts moot.

4) P. ramorum in the East

According to the most recent newsletter of the California Oak Mortality Task Force, over the nine years since 2010, the pathogen has been detected from 11 streams in six eastern states – four in Alabama; one in Florida; two in Georgia; one in Mississippi; one in North Carolina; and two in Texas. P. ramorum has been found multiple times in eight of these streams; it is consistently present in two steams in Alabama, one each in Mississippi and North Carolina.

In 2018, seven states participated in the stream survey (which is operated by the USDA Forest Service):  (AL, GA, MS, NC, PA, SC, and TX). This was the smallest number of participating states, which has fallen from14 in 2010 to seven in 2018.

The number of streams surveyed annually has ranged from 45 to 95. The number of streams sampled in 2018 was also close to the smallest number: 47. P. ramorum was detected from six streams – four in Alabama, one each in Mississippi and North Carolina. All positive streams were associated with previously P. ramorum-positive nurseries.

Remember that P. ramorum continues to be detected in West Coast nurseries that ship plants interstate (see the second section of this blog).

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.

2018 – More Bad News on Sudden Oak Death

Tanoak mortality at Big Sur photo by Matteo Garbelotto
  1. Outbreaks intensified in western North America and Western Europe (UK, France).
  2. Outbreaks are increasingly genetically diverse – raising the possibility of sexual reproduction and evolution.
  3. Evidence accumulated that eradicating Phytophthora ramorum from the environment once it is present is extremely difficult, if not impossible.

Meanwhile, APHIS proposed revisions that would weaken its regulation of nursery stock. See my earlier blog. Copies of all comments can be viewed here.

1) Intensifying Outbreaks

North America

According to the California Oak Mortality Task Force’s (COMTF) November 2018 newsletter, about 50 million trees have been killed by P. ramorum in California and Oregon. This breaks down to:

  • 29 – 44 million tanoaks (Notholithocarpus densiflorus) (1.6 – 2.5% of the species’ total population in California and Oregon);
  • 1.9 – 3.3 million coast live oaks (Quercus agrifolia) and Shreve oaks (Q. parvula var. shrevei), combined (0.4 – 0.7% of their populations); and
  • up to 1.1 million California black oaks (Q. kelloggii) (less than 0.17% of their population).

Of course, the oaks face additional threats from goldspotted oak borer and  polyphagous and Kuroshio shot hole borers hin more southern parts of California.

California bay laurel (Umbellularia californica) is not killed by P. ramorum but instead drives the spread of the outbreak in California. The state has an estimated 91.4 million infected California bay laurel trees.

These estimates are considered to be conservative. They are based only on trees that have been confirmed to be infected by direct, cultural isolation during the period up to 2014 — more than four years ago! And before a sharp intensification of infection (see below).

Data from a USDA Forest Service aerial detection survey – reported in COMTF’s September 2018 newsletter — detected a large increase in tanoak mortality in counties California counties reaching from Mendocino south to Monterey. This intensification in tree mortality was expected because the pattern is already well established: two seasons after a wet winter seasons, trees die. Such a wet and extended winter occurred in 2016-2017.

United Kingdom

Outbreaks of the EU1 strain of P. ramorum on larch (Larix kaempferi) in Scotland have also intensified. The infection is now found throughout much of Scotland, not just in the heavily infested zone in the the southwest part of the country. See updated map of outbreaks on Larch sites in woodland settings at https://scotland.forestry.gov.uk/supporting/forest-industries/tree-health/phytophthora- ramorum?highlight=WyJyYW1vcnVtIiwiJ3JhbW9ydW0iLCIncmFtb3J1bSciXQ

–

There is more on the status of P. ramorum in the the UK (England, Wales, Scotland and Northern Ireland) in a situation report posted by Forestry Commission England in 2018. Find it here: https://www.forestry.gov.uk/pdf/PRamorumSituationReport30June2018.pdf/$FILE/PRamorumSituationReport30June2018.pdfh

As in North America, the large number of outbreaks is attributed to favorable, wet conditions in the summer and fall of 2017. (This situation was summarized in COMTF’s September 2018 newsletter.

France

The outbreak on larch in France, first reported in 2015, is also spreading. This is particularly significant because, first, it is the first report of  P. ramorum outside of nurseries and ornamental settings in mainland Europe and, second, because it is a new genotype not tied to any other outbreak. By May 2018, about 80% of the trees in the Saint-Cadou larch plantations in Brittany (Northwest France) were symptomatic or dead in the more infected plots. A second outbreak has been detected a few kilometers away in a mixed forest stand of larch, oak, and sweet chestnut (Castanea sativa).  There, disease prevalence was much lower. Both stands have been removed.

(This was also  summarized in COMTF’s September newsletter.

2) Increasing Genetic Diversity

EU1 Strain in Oregon

As I have reported in the past, Oregon now has a second strain of Phytophthora ramorum – the “EU1” strain. This opens the possibility of sexual reproduction between it and the NA1 strain already established in forests in Oregon’s Curry County.

According to a presentation by Chris Benemann of the Oregon Department of Agriculture to the Continental Dialogue on Non-Native Forest Insects and Diseases, in 2018 – three years after the initial detection of one tree in 2015 – the number of trees infected by the EU1 strain has risen to 73. Oregon has prioritized removing these trees and treating (burning) the immediate area – now more than 355 acres. The legislature has provided $2.3 million for SOD treatments for 2017-2019. ODA believes that eradication of the EU1 outbreak is still possible.

3) But Is Eradication Possible?

According to the COMTF September newsletter, P. ramorum was detected by a water bait in a small pond downstream from a previously-infected botanical garden in Kitsap County, Washington. The garden undertook extensive mitigation efforts – including soil steaming –  and the pathogen had not been detected in this managed landscape for about 2 ½ years. Hundreds of samples of host plants were collected in September, with only one warranting further analysis to determine whether it was positive.  Surveys will continue in 2019.

In the East, USDA has baited streams to detect P. ramorum for several years. Seven states participated in the 2018 Spring National P. ramorum Early Detection Survey of Forests: Alabama, Georgia, Mississippi, North Carolina, Pennsylvania, South Carolina, and Texas. As reported in the COMTF’s September newsletter, h292 samples were collected from 48 sites. As in past years, positive samples were collected from streams associated with previously positive nurseries. These included three samples from two locations in Alabama; two samples from one location in Mississippi; and one sample from North Carolina. The Alabama and Mississippi sites have tested positive for approximately a decade.

So, the pathogen is persisting in water – but how? I have been told that P. ramorum requires plant material on which to survive – so how is it persisting without detectable infested plants? Also, does the presence of zoospores pose a threat of infesting streamside plant material? What studies are examining this issue?

Awareness through Art

Artists have transformed a SOD-infected tanoak tree into 7,000 pencils as part of their thoughtful “7,000 Marks” project. They  explore issues around global industrial trade, quarantine boundaries as a conservation tools, and the opposing concern that restricting trade can echo a rising tide of xenophobia. You can learn more (and buy pencils) here.

SOURCES

Cobb, R.; Ross, N.; Hayden, K.J.; Eyre, C.A.; Dodd, R.S.; Frankel, S.; Garbelotto, M. and Rizzo, D.M. 2018. Promise and pitfalls of endemic resistance for cultural resources threatened by Phytophthora ramorum . Phytopathology. Early view.

https://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO-04-18-0142-R

Harris, A.R.; Mullett, M.S.; Webber, J.F. 2018. Changes in the population structure and sporulation behaviour of Phytophthora ramorum associated with the epidemic on Larix (larch) in Britain. Biological Invasions. 20(9): 2313–2328.

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.

Alarming Picture of Phytophthora Threats to Forests World-wide

Phytophthora dieback in West Australia


Prompted by the rising number of Phytophthora-caused diseases in forests on several continents, in 1999 the International Union of Forest Research Organizations (IUFRO) formed the IUFRO Working Party 7.02.09 ‘Phytophthora Diseases of Forest Trees’. Last spring This group published a global overview of Phytophthora diseases of trees (Jung et al. 2018; see full citation at the end of this blog).

The study covers 13 different outbreaks of Phytophthora-caused disease in forests and natural ecosystems of Europe, Australia and the Americas.

The picture is alarming!

Jung et al. state definitively that the international movement of infested nursery stock and planting of reforestation stock from infested nurseries have been the main pathway of introduction and establishment of Phytophthora species in these forests.  

The Picture: A Growing List of Diseases, Species, and Places Affected,

Jung et al. note that, during the past six decades, the number of previously unknown Phytophthora declines and diebacks of natural and semi-natural forests and woodlands has increased exponentially. The vast majority of these disease complexes have been driven by introduced invasive Phytophthora species. In 1996, 50 Phytophthora species were known. In the 20 years since then, more than 100 new Phytophthora species have been described or informally designated. One study (Tsao 1990) estimated that more than 66 % of all fine root diseases and more than 90 % of all collar rots of woody plants are caused by Phytophthora spp. Many of these had previously been attributed to abiotic factors or secondary pathogens. One example – surprising to me, at least – is that decline of mature beech trees in Central Europe is linked to Phytophthora rather than beech bark disease!

Several of the disease complexes described in Jung et al. 2018 are causing heartrending destruction of unique floras, e.g., jarrah, tuart, and other communities of western Australia and kauri forests of New Zealand. The authors expect increasing damage to the Mediterranean maquis in the future. They list these among other examples:

  1. Ink disease of chestnuts worldwide
  2. Oak declines and diebacks in Europe and North America
  3. Decline and mortality of alders (Alnus species) in Europe
  4. Decline and mortality of Port-Orford cedar (Chamaecyparis lawsoniana) in Europe and North America
  5. Kauri dieback in New Zealand link to earlier blog
  6. Decline and mortality of Austrocedrus chilensis and Juniperus communis in Argentina and Europe
  7. Diebacks of natural ecosystems in Australia
  8. Decline and dieback of the Mediterranean maquis vegetation
  9. Decline and dieback of European beech in Europe and the US
  10. Dieback and mortality of southern beech (Nothofagus species) in the United Kingdom and Chile
  11. ‘Sudden Oak Death’ and ‘Sudden Larch Death’ in the US and United Kingdom
  12. Leaf and twig blight of holly (Ilex aquifolium) in Europe and North America
  13. Needle cast and defoliation of Pinus radiata in Chile

Several of the Phytophthoras are causing severe damage on several continents:

  • P. cinnamomi in Europe, North America, and Australia
  • P. austrocedri in South America, Europe, and western Asia
  • P. ramorum in Europe and North America
  • P. lateralis in North America and Europe.

Often, the genetic makeup of the Phytophtoras species varies in these different locations. These differences indicate separate introductions and the existence of sexual reproduction and continuing evolution in response to conditions.

Why Phytophthoras are Spreading via the Plant Trade and Nursery Practices

First, Phytophthora species are able to survive unsuitable environmental conditions over several years as dormant resting structures in the soil or in infected plant tissues. When environmental conditions become suitable, the resting spores germinate – often prolifically. Since visible symptoms might not appear for considerable time after infection because the mechanism is progressive destruction of the fine root system, detection of the disease is delayed, further undermining control.

Second, most of the Phytophthora species causing  disease complexes were unnoticed as co-evolved species in their native environment. Often they were unknown to science before their introduction to other continents – where they become invasive on naïve plant species. Consequently, these species are not captured by the international plant health system, which is based on lists of recognized “pest” species.

Third, the common nursery practice of applying fungicides or fungistatic chemicals masks the presence of pathogens – another way plants pass unnoticed through phytosanitary controls. These chemicals do not, however, kill the pathogen. 

Fourth, the importation into receiving nurseries of plants from around the world provides ample opportunity for the introduced Phytophthoras to hybridize. The interspecific hybrids may differ in host range and virulence from the parent species, thus making predictions about the potential effects of an ongoing invasion even more difficult.

Fifth, the nurseries or plantings in gardens or restoration projects also provide suitable environments for prolific germination and spread.

All of these risks were first enumerated by the eminent British pathologist Clive Brasier a decade ago! (See Brasier et al. 2008 citation at the end of the blog.)

As Jung et al. 2018 point out, the scientific community has repeatedly urged regulators to require the use of preventative system approaches for producing Phytophthora-free nursery stock (see references in the article). Scientists have provided research-based guidance to reduce the risk of infestation. Such measures are being implemented by only some nurseries in the US. For example, USDA APHIS has specific requirements for nurseries that ship hosts of P. ramorum in interstate commerce after the nurseries or the plants have tested positive.  More broadly, APHIS, the states, and the nursery industry are in the second round of pilot testing of an integrated measures approach to managing all pests under the Systems Approach to Nursery Certification (SANC) program

At the international level, the International Plant Protection Convention has adopted ISPM#36, which also envisions greater reliance on systems approaches.  However, the preponderance of international efforts to protect plant health continue to rely on visual inspections that look for species on a list of those known to be harmful. Yet we know that most damaging Phytophthoras were unknown before their introduction to naïve ecosystems.

Furthermore, use of fungicides and fungistatic chemicals is still allowed before shipment.

As pointed out by several experts beginning with Dr. Brasier but including  Liebhold et al. 2012, Santini et al. 2013, Jung et al. 2016, Eschen et al. 2017, this approach has failed to halt spread of highly damaging pathogens. (I note that the list of such pathogens is not limited to Phytophthoras; see the description of ohia rust in Hawai`i, Australia, and New Zealand).

Jung et al. 2018 also call for increasing the genetic resistance of susceptible tree species. The authors regard this as the most promising sustainable management approach for stabilizing declining natural ecosystems and for reintroducing susceptible tree species at sites with high disease impact. See my blogs about efforts to enhance U.S. tree-breeding posted earlier this year.


SOURCES

Brasier CM. 2008. The biosecurity threat to the UK and global environment from international trade in plants. Plant Pathology 57: 792–808.

Jung T, Orlikowski  L, Henricot B, et al. 2016. Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora diseases. Forest Pathology 46: 134–163.

Jung, T., A. Pérez-Sierra, A. Durán, M. Horta Jung, Y. Balci, B. Scanu. 2018. Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands. Persoonia 40, 2018: 182–220   Open Access!

Liebhold AM, Brockerhoff  EG, Garrett  LJ, et al. 2012. Live plant imports: the major pathway for forest insect and pathogen invasions of the US. Frontiers in Ecology and Environment 10: 135–143.

Santini A, Ghelardini L, De Pace C, et al. 2013. Biogeographic patterns and determinants of invasion by alien forest pathogens in Europe. New Phytologist 197: 238–250.

Tsao PH. 1990. Why many Phytophthora root rots and crown rots of tree and horticultural crops remain undetected. Bulletin OEPP/EPPO Bulletin 20: 11–17

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.

APHIS’ Strategic Plan – Focus on Deregulation & Trade Facilitation

APHIS’ headquarters building

USDA APHIS released its Strategic Plan for fiscal years 2019-2023 just after Thanksgiving. The report is 21 pages long. There is no evidence that any stakeholders were asked for input or review.

The Plan has a disappointing – but not surprising – emphasis on deregulation and “customer service”. A second – and more surprising weakness is the lack of attention to plant pests – even those of agriculture, much less natural resources. The emphasis is clearly on animal pests and diseases – including zoonotics.

APHIS’ mission is “To safeguard the health, welfare and value of American agricultural and natural resources.” To accomplish this mission, APHIS has set three goals:

  • Deliver efficient, effective, and responsive programs.
  • Safeguard American agriculture.
  • Facilitate safe U.S. agricultural exports.

Most references to protecting natural resources relate to finding more environmentally sensitive approaches for the program under which APHIS reduces human-wildlife conflicts (e.g., birds being struck by airplanes).

In the Plan, APHIS Administer Kevin Shea writes in his opening message that achieving APHIS’ difficult mission of protecting the health and value of America’s agriculture and natural resources cannot be accomplished by APHIS alone. Instead, the agency must work collaboratively with other government agencies and industry, and consult regularly with partners and stakeholders regarding programs’ effectiveness. Administer Shea also highlights the importance of “delivering our programs and services efficiently, effectively, with integrity, …” The agency promises to modernize information technology, data management, methods of communication with collaborators, exporters and importers, etc., in order to give good return on expenditure of taxpayer resources. APHIS also pledges to make decisions based on science. There are seven references to basing decisions on scientific data.

Fair enough. Such emphases were to be expected from Trump Administration and prefigured by USDA Secretary Sonny Perdue during his nomination hearing, e.g., facilitating exports, supporting better information technology.

However, the Plan refers to “customer service” or “customer experience” 34 times. An additional seven references are made to reducing regulatory burdens. The Plan also speaks of the need to “protect the health, welfare, and value of American agriculture and natural resources. … at a reasonable cost. … Easing regulatory burdens makes it easier to create jobs and promote economic growth.” (Emphasis added.)

Perhaps the recent proposal to deregulate the emerald ash borer is driven in part by the emphasis on minimizing costs to regulated industries and seeking alternative approaches? (Although the deregulation has been under discussion for several years, predating the Trump Administration.)

from APHIS PPQ website

The imbalance in attention to animal versus plant pests and disease is striking. Each of the 14 goals is supported by a number of specific tactics. There are a total of 100 “tactics” under the two goals most directly relevant to preventing or managing pest introductions. These goals are: “Protecting America’s agriculture” and “Promoting U.S. agricultural exports.” Of the 100 tactics, only ten are clearly related to plant pests; 19 are pretty clearly activities that apply to both plant and animal pests and diseases; and five are unclear as to whether they include plant pests as well as animal diseases. Thus, only a third of the tactics apply!

[In making this calculation, I did not include 43 tactics listed under the first goal (“Deliver efficient, effective, and responsive programs”) or three objectives under the goal of “Protecting American agriculture” that apply explicitly to wildlife management, regulating genetically engineered organisms, or ensuring humane treatment of animals.]

Specific examples of such lack of balance include the six examples illustrating the declaration (on p. 4) that “Pest and disease events are more frequent, more complex, and less predictable.” Five of the examples are animal diseases, the sixth is the insect-vectored human disease caused by the Zika virus.

In discussing its efforts to balance its safeguarding efforts against increasing requests for market access by international trading partners, APHIS mentions some activities pertinent to plant as well as animal pest management, e.g., examining disease and pest risks and inserting mitigation strategies into international agreements and interstate movement protocols. However, the only specific action it mentions is helping countries to build capacity to implement the Global Health Security Agenda.

The only reference to forest pests is under one of the 24 tactics associated with Goal 2. Safeguard American agriculture, Objective 2.1: Prevent damaging plant and animal pests and diseases from entering and spreading in the United States to promote plant and animal health. This tactic calls for strengthening the North American perimeter against pest threats from outside the region to prevent introduction of agricultural, forest, and other invasive pests.

Why are Plant Pests slighted?

Perhaps plant-related efforts were left out because they are less “sexy”? Or because they are more distantly linked to human health? The Plan does state that “The tactics in this plan represent only a portion of APHIS activities and by no means embody all the important work APHIS does to fulfill its mission.”

Who knows what was left out?

How will adoption of this strategy affect future efforts to address tree-killing insects and pathogens – both those already present in the country and those yet to be introduced?

Might PPQ Fill in the Gaps?

In 2014 APHIS Plant Protection and Quarantine issued its own strategic plan. This supplementary plan made frequent mentions of safeguarding natural resources. Indeed, the third of the plan’s seven goals stated:                              

Goal 3: Protect forests, urban landscapes, rangelands and other natural resources, as well as private working lands from harmful pests and diseases

Several “tactics” under each goal also directly applied to protecting natural resources. I list them below:

1) Prevent the entry and spread of ag pests and diseases.

  • Coordinate with Canada to implement an effective multi-national system that reduces the threat of tree pests arriving from Asia and other parts of the world (e.g. AGM).

3: Protect forests, urban landscapes, rangelands and other natural resources, as well as private working lands from harmful pests and diseases

  • Maintain EAB regulatory framework to focus on the leading edge of infestations while minimizing impacts on regulated businesses in quarantined areas.
  • Evaluate the effectiveness of biocontrol releases in states and combining both regulatory & outreach activities to address the risks of moving logs, firewood, and nursery stock.
  • Examine detection technologies and partnering with states to determine and apply the most effective strategies to survey & eradicate the Asian longhorned beetle
  • Partnering with federal and state agencies to enact measures such as a public outreach campaign to mitigate the movement of forest pests through firewood.
  1. Ensure the safe trade of ag products, creating export opportunities for U.S. producers
  • play a leadership role in revising ISPM#15
  1. Protect the health of U.S. agricultural resources, including addressing zoonotic disease issues and incidences, by implementing surveillance, preparedness and response, and control programs
  • Strengthen partnerships with Tribal Nations to develop a robust surveillance and early detection system for detecting and reporting invasive species.
  • Work with all stakeholders to coordinate all-hazards agriculture and natural resources response support.
  • Develop science-based programs in collaboration with industry and academia to jointly identify practices that will mitigate pest damage. E.G., SANC program http://sanc.nationalplantboard.org/ [a Systems Approach to Nursery Certification] implemented jointly with the National Plant Board and nursery industry

Dare we hope that PPQ adopts an updated strategic plan that fills in some of the gaps in the overall APHIS plan?

 

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.

 

Report Lists Non-Native Species in the U.S.

Ailanthus altissima

Several scientists at the United States Geological Service (USGS) have published a report and accompanying datasets that attempts to provide a publicly accessible and comprehensive list of non-native species established in United States.

Led by Annie Simpson and Meghan C. Eyler, a team of six scientists worked six years (2013–2018). They reviewed 1,166 authoritative sources to develop a list of 11,344 unique names – most of them binomials (genus and species), a few genera, plus some viruses.

This was a Herculean effort that produced very valuable products. We are all in their dept!

Simpson and Eyler point out that knowing which species are non-native to a region is a first step to managing invasive species. Lists compiled in the past were developed to serve a variety of purposes, including watch lists for preventing invasions, inventory and monitoring lists for research and modeling, regulatory lists for species control, and non-regulatory lists for raising awareness. As a result, they are not comprehensive.

Among the sources these authors consulted in preparing the list were peer-reviewed journal articles, books, brochures, circulars, databases, environmental assessments, technical reports, graduate theses, and websites.

Data – by Region

The report also notes which non-native species were established in each of three regions: the “lower 48” states, Alaska, and Hawai`i. Not surprisingly, more than half the non-native taxa are established in the vast area (nearly 7.9 million km2) comprising the “lower 48” states – 6,675 taxa. Almost half of the total number of non-native taxa have established in the tiny geographic region (only 28,311 km2) of Hawai`i – 5,848 taxa.  One-tenth as many non-native taxa – 598 – are reported as established in Alaska (1.7 million km2).

This report includes taxa that are not native to any part of the specific region, but established (naturalized) somewhere in the region. An “established” species must have at least one population that is  successfully reproducing or breeding in natural systems. The list includes domesticated animals and plants introduced for crops or horticulture when the taxon has escaped cultivation or captivity and become established in the wild. Species listed range from feral hogs (Sus scrofa) to plum pox virus and citrus canker to ohia rust (Puccinia psidii).

Of the total 11,344 taxa, 157 are established in all three regions. These included 125 vascular plants (especially grasses and asters); 13 arthropods, 11 mammals; 6 birds; 3 mollusks; 1 bryozoan. One of the ubiquitous plant species is tree of heaven (Ailanthus altissima). I find it entirely appropriate that the cover photo shows this tree – the photo was taken 8 miles from my home in Fairfax County, Virginia.

Nearly three-quarters (71.4%) of the non-native species in Alaska are plant species. More than half (59.7%) of the non-native species in the “lower 48” region are also plants. Nearly all the remainder of the non-native species in both regions are some kind of animal. Fungi constitute only 1.8% of the non-native species in the “lower 48” region; all the rest of the groups (Bacteria, Chromista, Protozoa, Virus) constitute less than 1% of the non-native species recorded in either region.

By contrast, in Hawai`i, animals make up 69.7% of the listed non-native species; most are invertebrates. Plants constitute 29.8% of the Hawaiian list.

Gaps, by Taxon

The authors recognize that invertebrates and microbes are under-represented because species are still being discovered; non-charismatic and difficult-to-identify species tend to be overlooked; and the species composition of any nation in this era of globalization is constantly subject to change.

I have noted some gaps among the pathogens: the absence of some of the Phytophthora that have been detected infecting shrubs and herbaceous plants in California,  e.g., Phytophthora cambivora, siskiyouensis, tentaculata;  and the “rapid ohia death” pathogens, Ceratocystis huliohia and C. lukuohia. Dr. Simpson is aware of these gaps and is soliciting sources to help add these organisms – especially the various Phytophthora species – to the next version of the list.

Simpson and Eyler note that the relative geographic distribution of the list at its current state seems to reinforce three well established premises: that tropical island systems are particularly vulnerable; that higher latitudes host fewer but are not invulnerable; and that species diversity in general decreases with increasing latitude.

 Comparisons to Other Databases

After standardizing the names in the list by comparing them to the Integrated Taxonomic Information System (ITIS), Simpson and Eyler also reviewed the USGS BISON database, which has more than 381 million occurrence records for native and non-native species in the U.S. and Canada, covering 427,123 different taxa. (The BISON database contains significantly more species occurrences for the U.S. than the largest invasive species database, EDDMapS, which contained 4.4 million species occurrences as of June 2018.) Simpson and Eyler had to evaluate which of these taxa met their definition of non-native, since most species occurrence records in the USGS BISON are not labeled as non-native in the original records.

Comparing the BISON and non-native lists, Simpson and Eyler found that the BISON list contained a larger number of occurrence records for non-native taxa: a total of 13,450,515.However, the BISON list does not provide complete coverage of non-native species: it includes records for 77% of list of non-native species Simpson and Eyler found in Alaska, 75% of the “lower 48” sublist, but only 37% of the Hawaiian sublist.

Simpson and Eyler state their intention to continue updating the list of non-native species, they welcome contributions to it from area experts, and they urge integration of new occurrence data into invasive species database such as EDDMapS.

Indicators of Non-Native Species Richness

Figure 3 in the report (above) maps the number of non-native taxa in BISON at the county level. Figure 4 displays the proportion of non-native to native species in BISON. Higher percentages are generally evident in coastal areas and other regional hotspots. For example, the proportion in Hawaiian counties is greater than 33%. Additional data are needed to perform a more in-depth analysis of non-native species richness and abundance.

UPDATE! New Report in the Works

In June 2021, USGS announced that it was updating its Comprehensive List of Non-Native Species Established in 3 Major Regions of the U.S. so that the document more closely aligns with the parameters of the Global Register of Introduced and Invasive Species. The new USGS dataset is to be called the US Register of Introduced and Invasive Species. The list in the current draft includes 15,364 records. About 500 of these records are in Alaska, 6,000 in Hawai`i, and 8,700 in the conterminous 48 States.

One of the lead authors, Annie Simpson, contacted invasive species experts seeking feedback and suggested additions – based on authoritative resources such as peer reviewed journal articles, pest alerts, databases, books, and technical bulletins. She sought input by 25 July, 2021.

The published version of this dataset will be made freely available on USGS’ ScienceBase (https://www.sciencebase.gov), and all reviewers will be acknowledged in the dataset’s abstract.

SOURCE

Simpson, A., and Eyler, M.C., 2018, First comprehensive list of non-native species established in three major regions of the United States: U.S. Geological Survey Open-File Report 2018-1156, 15 p.

The report and accompanying data tables are available here.

South African report

In an unrelated but similar development, South Africa has issued a report on its invasive species — 2017 The Status of Biological Invasions and Their Management in South Africa. The report analyzes pathways of introduction and spread; number, distribution and impact of individual species; species richness and abundance of alien species in defined areas; and the effectiveness of interventions. The report notes that 775 invasive species have been identified to date, of which 556 are listed under some national regulatory program. Terrestrial and freshwater plants number 574 species; terrestrial invertebrates number 107 species. (This total does not include the polyphagous shot hole borer, which was detected too recently.) 107 species are considered by experts to be having either major or severe impacts on biodiversity and/or human wellbeing. Alien species richness is highest in the savanna, grassland, Indian Ocean coastal belt and fynbos biomes, lower in the more arid Karoo and desert biomes. South Africans are particularly focused on the reductions in surface water resulting from plant invasions. The decades-old “Working for Water” program has two goals: providing employment and development opportunities to disadvantaged individuals in rural areas, and managing invasive alien plants.

The Status of Biological Invasions and Their Management in South Africa is available here.

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.

Worldwide – and U.S. – Proliferation of Phytophthora via the Nursery Trade – an Update

Phytophthora cinnanomi killing Ione manzanita in California; photo from Swiecki and Garbelotto, Distribution of Phytophthora cinnamomi within the range of Ione manzanita (Arctostaphylos myrtifolia).   Agreement between the California Department of Fish and Game and University of California

Phytophthora species are plant pathogens in the oomycote group (water molds, closely related to brown algae). More than 160 species have been described; new species are continually being isolated. Many Phytophthora species are deadly to naïve hosts; examples in the United States include sudden oak death, Port-Orford cedar root disease, disease on chestnuts and oaks.

Forests in Europe – especially the United Kingdom – and Australia are also suffering high levels of mortality associated with one or more Phytophthora species.

In recent years, several studies have documented the role of nurseries in spreading non-native Phytophthora species. Two strains of P. ramorum are widespread in European nurseries and in tree plantations and wild heathlands of southwest England, Wales, parts of Scotland, and Ireland. (See here and here.)

In April 2016 I blogged about the situation in Europe described by Jung et al. 2015 (see references at the end of the blog). Jung et al. concluded that diseases caused by Phytophthora pose a substantial threat to both planted landscapes and forest ecosystems across Europe. They found 56 Phytophthora taxa in 66% of 2,525 forest and landscape planting sites that were probably introduced to those sites via nursery plantings.

Barber et al. 2013 reported nine species of Phytophthora associated with a wide variety of host species in urban streetscapes, parks, gardens, and remnant native vegetation in urban settings in Western Australia. Phytophthora spp were recovered from 30% of sampled sites.

A new summary confirms that the threat is similar in North America. In British Columbia, Dale et al. (2017) found more than two times as many Phytophthora species were detected in soil and water samples in urban areas (23) than in natural areas (11). Urban samples also showed a much higher diversity of Phytophthora per site than natural environments. These Phytophthora species had been introduced initially into urban areas and had subsequently spread into native vegetation, particularly in areas near developed sites (wildland-urban interface areas).

Swiecki et al 2018 cite several sources and their own studies to show that the large and increasingly diverse contingent of introduced Phytophthora species pose an increasingly important threat to both urban forests and surrounding native forests and plant communities in California. It is clear that shrubs and herbaceous plants as well as trees are also at risk. These scientists have repeatedly found multiple non-native Phytophthora species at individual sites in northern and southern California sites where nursery stock had been planted. Sampling in 2014 identified about 60 different Phytophthora taxa in restoration planting sites and native plant nurseries. The sampled restoration plantings were mostly located in urban riparian corridors and peri-urban parks, open spaces, or protected watersheds.

I first discussed this issue in a blog in July 2016.

Swiecki et al (2018) have also found that Phytophthora species persist in drier ecosystems. When conditions are too dry for sporangium production, Phytophthora hyphae produce resistant survival structures that can tolerate drying and persist in dead root fragments or soil. In the presence of appropriate stimuli, e.g., moisture and root exudates, resistant structures germinate to produce sporangia or hyphae, leading to new infections. Even relatively short wet periods associated with rain or irrigation can be sufficient to stimulate zoospore release. Swiecki et al (2018) list examples of numerous Phytophthora infestations that developed in dry sites, such as dry foothills of the Sierra Nevada in Amador County, and the Oakland Hills of Alameda & Contra Costa County. Swiecki et al. (2018) also  note that P. cinnamomi has persisted in Australian forests in the absence of known primary hosts.

Phytophthora infections can also persist for decades in soil. In California, Swiecki et al. (2018) mention several examples:

  • Residual cinnamomi inoculum killed young sprouts of susceptible manzanitas (Arctostaphylos myrtifolia and A. viscida) planted on sites that were infected many years earlier.
  • A street planting of cork oaks (Quercus suber) apparently died due to Phytophthora root rot that had occurred 21 years earlier.
  • Both cinnamomi and P. cactorum were recovered from roots and soil beneath affected trees at least 60 years after the site had been a municipal woody plant nursery and adjacent residence.
  • A 7-acre area of native vegetation showing decline & mortality of multiple plant species was infested with multiple Phytophthora spp, including cactorum, P. cambivora, P. crassamura, P. ‘kelmania’ & P. syringae. The site was apparently infected 22 years earlier during a planting of a habitat restoration project using Ceanothus nursery stock. Subsequent spread was primarily downhill from the planting sites, facilitated by water flow, with additional spread along and near trails.

 

The Risk from the Nursery Trade

While Phytophthora-infested soil and plant debris can be transported on tools, vehicles, and shoes, or moved in large quantities when infested soil is excavated, graded, or imported, the principal threat is the nursery trade.

  • Jung et al. (2015) state that widespread contamination of nursery stock was the primary means by which these pathogens were introduced and spread in Europe. They found 49 Phytophthora taxa in 670 European nurseries. Phytophthora species were recovered from more than 90% of the sampled nurseries.
  • Swiecki et al. (2018) say that most of the common Phytophthora species detected in California are distributed globally, moved about with live plants or other infested materials. None is native to California.
  • Swiecki et al. (2018) cite studies reporting that thirteen species of Phytophthora were found in a survey for leaf spots in California nurseries in 2005 and 2006. Sampling of plants in or originating from Calif native plant nurseries alone has yielded about 60 Phytophthora At least eight species of Phytophthora were found in shipments of symptomatic and asymptomatic plants sent from west coast nurseries to Maryland. Parke et al. (2014) identified 28 Phytophthora taxa in four Oregon nurseries.
  • Not all infections are on the West Coast. Swiecki et al. (2081) reports that a survey in Minnesota nurseries of plants with symptoms – primarily on aboveground plant parts – found eleven species of Phytophthora.

Are scientists in other parts of the country looking for Phytophthora? I see no reason to think the situation in California is unique.

The damage caused by Phytophthora infections can be significant. In California and Oregon, sudden oak death,  and Port-Orford cedar root disease, have killed well over a million trees and disrupted the ecosystems of which they are a part. There are multiple locations in Northern California where introduced Phytophthora species, especially P. cinnamomi and P. cambivora, have caused localized to extensive decline and mortality in native forests and shrublands.

Phytophthora dieback has infected more than one million hectares in Western Australia. More than 40% of the native plant species of the region are vulnerable to the causal agent, P. cinnamomi.

Phytophthora dieback in Western Australia

 

Dieback in native forest in Western Australia; photo copyright Western Australian Department of Parks and Wildlife

In the United Kingdom, several Phytophthora species are causing widespread mortality of native shrubs and trees and commercial plantings.

In nearly all the studies, scientists have detected previously unknown pathogen-host relationships.

The threat from spreading pathogens with wide host ranges is not limited to the genus Phytophthora. The fungus Fusarium euwallacea associated with the Kuroshio and polyphagous shot hole borers  is known to kill at least 18 species of native plants in California and additional species in South Africa.    The laurel wilt fungus kills many trees and shrubs in the Lauraceae family. ‘Ohi‘a or myrtle rust kills several shrubs native to Hawai`i and threatens a wide range of plants in the Myrtaceae family in Australia and New Zealand. Some insects also have wide host ranges, including the Kuroshio and polyphagous shot hole borers; and Asian longhorned and citrus longhorned beetles.

When are national and international phytosanitary agencies going to adopt policies and programs that are effective in preventing the continued spread of these highly damaging tree-killing pests? At the national level, APHIS needs to aggressively use two authorities to curtail importation of plant taxa from countries of origin which present a risk of transporting additional species of pathogens:

  • NAPPRA, which allows APHIS to prohibit risky imports until it has conducted a pest risk analysis.
  • Programs under the revised “Q-37” regulations allowing APHIS to work with exporting countries’ phytosanitary officials to implement integrated pest management strategies to ensure that plants are pathogen-free before they are exported.

I have blogged about both programs before – NAPPRA here;  the Q-37 regulation strengthening here.

At the international level, the members of the International Plant Protection Convention (IPPC) must recognize the failure of the international phytosanitary system and explore ways to strengthen it. See my numerous blogs on this topic (beyond those linked to here!) by visiting www.cisp.us or www.nivemnic.us and searching under the category “forest pathogens”.

 

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.

 

 

SOURCES

 

Jung, T. et al. 2015 “Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora disease” Forest Pathology. November 2015; available from Resource Gate

Swiecki, T.J., E.A. Bernhardt, and S.J. Frankel. 2018. Phytophthora root disease and the need for clean nursery stock in urban forests: Part 1 Phytophthora invasions in the urban forest & beyond. Western Arborist Fall 2018

Apparently can’t access current (2018) issues of “Western Arborist” on web unless subscribe

 

South Africa’s unique flora put at risk by polyphagous shot hole borer

The polyphagous shothole borer (PSHB) and its fungal symbiont Fusarium euwallaceae are killing trees in South Africa as well as in California.

File:Erythrina humeana, blomme, Manie vd Schijff BT, b.jpg

Erythrina humeana in the Manie van der Schijff Botanical Garden, Pretoria

The pest complex’s presence was detected in August 2017 through an international sentinel tree program – the first detection of a tree pest under the program. Under the ‘sentinel plantings’ program, staff at botanical gardens and arboreta monitor their holdings – often exotic species growing outside of their natural range – and alert program partners when they detect damage caused by insects or pathogen not previously known to pose a risk. The International Plant Sentinel Network (IPSN) was launched in 2013. Botanical gardens and arboreta in South Africa joined the international effort in 2016 (Paap et al. 2918 – see list of sources at the end of this blog).

PSHB-caused tree mortality was initially detected in the KwaZulu-Natal National Botanical Gardens in Pietermaritzburg in August 2017. Affected trees were London Plane (Platanus x acerifolia) (Paap et al. 2018).

A beetle collected in 2012 in Durban, 50 km away from Pietermaritzburg, has now been determined to belong to the Euwallacea fornicatus species complex – indicating that the invasive insect and fungal species have been established in South Africa for several years (Paap et al. 2018). [Interestingly, 2012 is also the year that Dr. Akif Eskalen detected PSHB in a backyard avocado in southern California – setting off the detection, research, and slow-the-spread efforts now under way there.]

 

2018-10-01 PSHB - South Africa

locations of PSHB detections in South Africa; map from http://polyphagous-shot-hole-borer.co.za/

South African authorities were immediately concerned because the beetle-fungus complex attacks such a broad range of trees (species in 58 plant families).  Hosts include several species native to southern Africa – including cabbage tree (Cussonia spicata), common calpurnia (Calpurnia aurea), monkey plum (Diospyros lycioides),  two species of coraltree (Erythrina humeana and E. lysistemon), huilboerboon (Schotia brachypetala), honey flower (Melianthus major), two alders (Cunonia capensis and Nuxia floribunda), and red orchid bush (Bauhinia galpinii). Also at risk are several commercial crop trees such as avocado (Persea americana), macadamia nut (Macadamia integrifolia), pecan (Carya illinoinensis), peach (Prunus persica), orange (Citrus sinensis) and grapevine (Vitis vinifera) and several ornamentals, including maple, holly, wisteria, oak and Camellia (Paap et al. 2018).

South Africa is home to a highly unique flora. Indeed, the “Cape Floral Kingdom” is the smallest of the six floral regions on Earth. For more about South Africa’s botanical importance, go here or here.

Rapid spread of the beetle-fungus complex appears likely because one of the most important reproductive hosts, castor bean (Ricinus communis) is a widespread woody weed in the KwaZulu-Natal region (Paap et al. 2018).

By July 2018, it was clear that PSHB was established in several parts of the country (see map). In George — a city along the southern coast, due east of Capetown, the beetle and fungus are affecting a wide range of indigenous and exotic trees in the botanical garden and the region‚ including box elder‚ Chinese and Japanese maple‚ oak‚ plane trees‚ Kapok trees‚ paper bark acacia‚ wild plum‚ dwarf corral and common corral (Chambers 2018).

In Johannesburg, a concerned citizen tracking the pest complex’ spread thinks that the beetle-fungus combination has already infested well over 100,000 of Johannesburg’s trees and is on track to damage or kill millions more (there are an estimated 6 – 10 million trees in Johannesburg, nearly all exotic) (Weltz 2018).

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.

SOURCES

Chambers, D.  “A 2mm beetle is laying waste to George’s trees” Sunday Times. 30 May 2018 https://www.timeslive.co.za/news/sci-tech/2018-05-30-a-2mm-beetle-is-laying-waste-to-georges-trees/

Johannesburg Urban Forest Alliance. The Shot Hole Borer Beetle is destroying our Urban Forest http://www.jufa.org.za/pshb.html

Paap, T., Z.W. de Beer, D. Migliorini, W.J. Nel,  M.J. Wingfield. 2018. Australasian Plant Pathology https://doi.org/10.1007/s13313-018-0545-0 https://link.springer.com/article/10.1007/s13313-018-0545-0

Weltz, A. Beetle Mania The Nasty Insect that is Killing the Trees of Johannesburg. Yale Environment 360; Published at the Yale School of Forestry and Environmental Studies. https://e360.yale.edu/features/beetle-mania-the-nasty-insect-that-is-killing-the-trees-of-johannesburg