David Smith and Ian Smith
a.) Office of the Chief Plant Health Officer, Victorian Department of Environment and Primary Industries
b.) School of Forest and Ecosystem Science, The University of Melbourne
c.) Bushbury Forest Pathology Services.


There are many threats to Australia’s Urban Forests from a combination of native and established introduced insects and pathogens (together defined as pests), and overseas exotic incursions (Tables 1 and 2).  Exotic pests that have become naturalised (established or endemic), have resulted in increased costs for tree management and in some cases placed doubts on their use as shade trees in parks and gardens.  Established introduced pests have also adversely impacted on biodiversity values (e.g. Phytophthora cinnamomi Table 1), and continue to pose a significant threat to the economic and ecological viability of forests in Australia.  Native pests have also caused significant damage in parks and gardens (e.g. Armillaria luteobubalina Table 1).  Due to their proximity to ports, urban forests potentially play a role in the pathway for the introduction of new exotic pests into the Australian landscape.

In the past, Australia has relied on its geographical isolation to provide a degree of natural protection from exotic threats. However, because of rapid transport of imports and exports into and out of Australia, quarantine measures alone are insufficient to protect our urban forests, unique ecology and the productivity of plant industries (PHA 2007).Australia’s reduced isolation in the modern world has been highlighted recently by an increased number of pest interceptions at border entry points (Table2).  Whilst a pest interception at our border does not usually result in the establishment of a pest, and reflects the diligence of quarantine staff and current procedures, it demonstrates potential pathways exist for their introduction, and the need for continued vigilance and support by tree management agencies, industry and the general public to detect those that may escape detection.

Recent trends in climate change also have potential adverse impacts, not only in potentially increasing the area affected and rate of spread of exotic incursions, but also adding to the range of pest species not currently considered as potential threats. A robust and effective biosecurity system is therefore essential to minimise the impacts such exotic pest incursions pose to trees in Australia.

Biosecurity in general can be described as the protection of the economy, environment and public health from the adverse negative impacts of exotic infectious pathogens, insects and other biological organisms (e.g. weeds).  It can be achieved by:

  • implementing measures that prevent new pests from entering Australia that potentially could become established (quarantine: pre-border and border)
  • establishing trapping and surveillance networks for pests so as to ensure early detection for those that break quarantine barriers(surveillance), and
  • preparing a response plan and capacity through appropriate preparedness to act swiftly and accurately to manage incursions with the aim of eradiation where possible, or containment to lessen their impact (response).

Urban forest biosecurity may be achieved through systems that aim to detect and prevent pest introductions or spread, or mitigate an outbreak if it occurs.  It is reliant on national and international policies and plans for dealing with a pest incursion, supportive tree management agencies, vigilant trained staff working in the arboriculture industry and an informed general public.

Stopping the entry, establishment and spread of unwanted pests is vital for protecting our urban landscapes, plant biodiversity and forest industries.This paper describes past, present and futures threats to urban trees in Victoria, Australia and highlights the importance of early detection and response.

Table 1.  Native and endemic*introduced pests of concern to urban forests in Victoria, Australia

Common Name Scientific name/s Biotic agent/damage Potential hosts Potential risk to Urban Trees Origin Native/Introduced
Armillaria root disease Armillaria luteobubalina Pathogen/root and butt rot Gymnosperms and angiosperms High Native
Autumn Gum Moth Mnesampela privata Insect/defoliator Eucalypts Seasonal Native
Chrysomelid Leaf Beetles Chrysophtharta, Paropsis spp. Anoplognathus spp Insect/defoliator Eucalypts Seasonal Native
Cypress Canker Seridium spp Pathogen/branch and stem canker Cupressaceae species High Introduced
Diplodia Diplodia pinea Pathogen/shoot blight and stem canker Pines and other conifers High/ stressed trees Introduced
Myrtle Rust (Eucalyptus rust,Guava rust) Puccinia psidii Pathogen/shoot and leaf death Myrtacae spp. Moderate, restricted by climate Introduced, under local containment
Five-spined Bark Beetle Ips grandicollis Insect/wood borer Eucalypts Moderate/ stressed trees Native
Palm Fusarium Wilt Fusarium oxysporum f. sp. canariensis Pathogen/vascular wilt Phoenix canariensis and other palms High Introduced, under local containment
Gum Leaf Skeletoniser Uraba lugens Insect/defoliator Eucalypts Seasonal Native
Light Brown Apple Moth Epiphyas postvittana Insect/defoliator Wide host range Seasonal Native
Longicorn beetles Phoracantha spp. Insect/ wood borer Eucalypts and other native species Moderate Native
Monterey Pine Aphid Essigella californica Insect/defoliator Pine species Seasonal Introduced
Phytophthora dieback Phytophthora cinnamomi and some other species Pathogen/root and collar rot Wide host range High Introduced
Pine Longhorned Beetle Arhopalus rusticus Insect/wood borer Pine species Low/stressed trees Introduced
Psyllids Psyllid species Insect/defoliator Eucalypts and other native species Seasonal Native
Sawflies Perga species and Phylacteophaga froggatti Insect/defoliator Eucalypts and other trees Seasonal Native
Sirex Wasp Sirex noctilio associated with fungal pathogen Insect/wood borer Pine species Low Introduced, under biological control
Sycamore Lace Bug Corythucha ciliate Insect/defoliator Platanus species High Introduced, not yet in Melbourne
Velvet-top Fungus Phaeolus schweinitzii Pathogen/butt rot Conifers Low/old age related Introduced

Table 2.  Exotic pests of concern to urban forests in Victoria, Australia (*border interceptions occured)

Common Name Scientific name Biotic agent/damage Potential hosts Potential risk to Urban Trees
Annosus root and butt rot Heterobasidion annosum Pathogen/root and butt rot Gymnosperms and angiosperms High
Armillaria root disease Armillaria spp. incl A.ostoyae and A. mellea Pathogen/root and butt rot Gymnosperms and angiosperms High
Asian gypsy moth* Lymantria dispar Insect/defoliator Wide host range High
Asian Longhorned beetle* Anoplophora glabriqennis Insect/wood borer Wide host range High
Brown mulberry longhorn beetle* Aprona germari Insect/wood borer Wide host range High
Chalara dieback Chalara fraxinea Pathogen/crown dieback Fraxinus species High
Chestnut Blight Cryphonectria parasitica Pathogen/branch and stem canker Chestnut, oak, red maple, shagbark hickory, and eucalypts High
Coniothyrium eucalypt canker Colletogloeopsis zulensis and C. gauchensis Pathogen/stem and branch canker Eucalypts Moderate, restricted by climate
Dutch Elm Disease Ophiostoma spp.i Pathogen with insect vector/ vascular wilt Elms High
Eucalyptus canker Chrysoporthecubensis Pathogen/branch and stem canker Eucalypts High
Emerald Ash Borer Agrilus planipennis Insect/wood borer Fraxinus species High
Eucalyptus leaf blight Phaeophleospora destructans Pathogen/defoliator Eucalypts Moderate, restricted by climate
Eucalyptus (guava) rust (other strains) Puccinia psidii Pathogen/shoot and leaf death Myrtacae species Moderate, restricted by climate
Japanese pine sawyer beetle* Monochamus alternatus Insect carries Pinewood nematode Pine species High
Mountain pine beetle Dendroctonus pondersoae Insect/wood borer Pine species High
Nectria canker Nectria fuckeliana Pathogen/stem canker Conifers Moderate
Nun moth Lymantria monacha Insect/defoliator Conifers High
Pitch canker Fusarium circinatum Pathogen/branch and stem canker Pine species High
Pinewood nematode Bursaphelenchus xylophilus Nematode/wilt Pine species High
Sycamore Lace Bug Corythucha ciliate Insect/defoliator Platanusspecies High
Ramorum dieback
(Sudden oak death)
Phytophthora ramorum Pathogen/shoot blight, stem canker Wide host range High
Phytophthora kernoviae Phytophthora kernoviae Pathogen/shoot blight, stem canker Wide host range High
Western gall rust Endocronartium harknessii Pathogen/stem galls Pine species High
White Spotted Tussock Moth Orgyia thyellina Insect/defoliator Rosaceaespecies High

Past threats

Pine nematode

The importance of early detection and eradication is shown by an incursion of a pine nematode (Bursaphelenchus hunanensis) within Melbourne in late 1999 (Hodda et al 2008, Smith et al 2008).  Local council officers reported a rapid decline of a mature pine tree (Pinus halepensis) in the botanic gardens at Williamstown, near Melbourne’s main port (Figure 1).  It is believed that the nematodes were introduced with wood boring insects that subsequently failed to establish.  The early detection and identification by council officers and DEPI diagnostic staff rapidly led to a nationally coordinated response to undertake surveys and remove all infested trees.

Figure 1. (a) Dying Pinus halepensis, (b) nematode extracted from wood, (c) Tree removal (d) load covered to prevent any insect escape (e) stump removal and disposal by either (f)burning or (g) deep burial

The rapid response prevented nematode establishment and potential spread into other urban trees and plantations.  In this case, the trees in the gardens close to the ports acted as ‘Sentinel Trees’ and the diligence of the local officers provided an early warning of the pest introduction enabling the successful response and eradication.

The pathway for the introduction for pine nematodes (Bursaphelenchusspp. and in particular B. xylophilus) still exists, and in 2009 and 2014, two more interceptions of the wood boring insect vectors occured in Melbourne (and Australia) when containers from abroad were opened near the ports (AQIS Nov/Dec 2009, DA 2014).  However, in theses later interceptions the insects were destroyed and no reports of dying trees were received.

Present threats

Myrtle rust

In April 2010 myrtle rust, initially described as Uredo rangelii, a member of the eucalyptus/guava rust complex of Puccinia psidii, was detected on a myrtaceous host Agonis flexusosa ‘After Dark’ by a cut flower grower on the central NSW coast. For many years P. psidii has been considered a high priority quarantine fungus.  Myrtle rust spread rapidly, and was detected in south east Queensland in late December 2010, and in Victoria in late December 2011. The incursion into Victoria was human assistedthrough transport of nursery plants. So far myrtle rust has only been detected in nurseries, private gardens and amenity plantings in Victoria, but is widely distributed in native forests along the east coast from Batemans Bay in southern NSW to the Daintree in far north Queensland. The host range has expanded rapidly to over 240 species from 34 genera of Myrtaceae. Several species are highly susceptible with potentially severe consequences for native fauna.

The fungus was first described on guava in Brazil in 1884 where it rarely caused damage, but by 1912 it had expanded its host range and was observed on Eucalyptus citriodora. Epidemics have occurred on Eucalyptus species planted in Brazil, on allspice in Jamaica (1938), on Melaleuca quinquenervia in Florida (1979) and on Metrosideros polymorpha in Hawaii (2005). It was reported in Japan in 2009 and China in 2011.

Symptoms vary between hosts and may consist of round lesions up to 1 centimetre in diameter, purple to brown in colour, which develop through the leaf to express on both the upper and lower leaf surfaces. The fungus produces bright yellow asexual spores and dark red-brown sexual spores often found together in pustules (Figure 2). Lesions turn dark brown to grey with age. Disease only affect young shoots, flowers, fruits and leaves, causing curling, buckling and distortion of tissues. Heavy infection causes shoot die back and defoliation.  Repeated infection may reduce vigour and result in plant death.

Figure 2. Symptoms and signs of myrtle rust (a) fungal spores, (b) yellow spores on the bottom of the leaf, (c) infected shoots with yellow spores.

Spores are dispersed by wind, rain-splash, animals and humans. Infection requires conditions of high relative humidity greater than 70 per cent, or a 6-8 hour period of leaf wetness, during low light or darkness. The optimum temperature for infection is 15-25 oC with a range of 2-40 oC. Lesions appear within 5-7 days and spores are produced up to 14 days or more after infection. Spores may survive for a week under field conditions. Studies conducted in Brazil on Eucalyptus show infection is favoured by a microclimate found from ground level up to a height of 4 metres. In laboratory studies exposure to light during the initial stage of infection reportedly inhibits infection.

Control of myrtle rust depends on maintaining good hygiene practises, fungicide application and plant resistance and breeding. Glasshouse studies in Australia have identified susceptible and tolerant Myrtaceae genera and species, and only a few resistant native plants.  Currently two fungicides are registered for disease control, while nine are permitted as is one surface sterilizing agent.

Asian longhorn beetle

The Asian longhorn beetle (Anolpophora glabripennis ALB) is a a polyphagous cerambycid native to China, Hong Kong, Korea and Japan where it causes widespread mortality to many tree species including elms, willow, poplar, maple and apple.Unlike many cerambycid species, ALB has enormous destructive potential because it attacks healthy trees and spends most of its life as a larva, boring inside tree trunks and large branches.  This boring activity by the larva compromises the tree’s vascular system, causes severe damage to the wood’s structural properties, and eventually leads to the death of the attacked trees (Cavey et al ., 1998).The adults can also cause defoliation and damage by feeding on leaves, petioles and bark.

In 1996, the beetle was first discovered in the United States, as well as Canada, Trinidad, and several European countries including Austria, France, Germany, Italy and the UK. The species is believed to have been accidentally introduced into these countries in solid wood packaging material (dunnage). ALB poses a significant threat to a range of deciduous hardwood species, including chestnut, ash and birch species and is the subject of costly eradication programs in many of these countries.  The full range of potential host species is yet to be elucidated.Due to extensive trade links with Asia, the risk of ALB interception  within Australia is high, with the most likely means of entry being through imported timber and wood products, including packing materials at major seaports.

An adult beetle is approximately 20 to 35 mm long and 7 to 12 mm wide. Its body is jet black in colour with white spots (Figure 3). The antennae are black with whitish-blue rings and can be up to two and a half times the body length (males have longer antennae). Beetle eggs (5 to 7 mm long) are laid under the bark within small oval pits that the female chews.  A single female beetle can chew between 35 to 90 individual depressions.  Once the eggs hatch, the larvae tunnel through the tree’s sap layers, effectively ringbarking the trees if enough larvae are present. The larvae can grow up to 50 mm long and can take up to 3 years to emerge as beetles. Adults emerge in summer, mate and subsequently lay eggs in a host tree’s bark. Adult beetles can live for up to 50 days. Because of the length of time that adult beetles may take to emerge, potential resources for surveillance is significant.

Figure 3. Asian longhorn beetle: (a) depressions chewed by a female beetle during egg laying (Donald Duerr, USDA Forest Service, Bugwood.org) (b) adult beetle (c) life cycle. (Joe Boggs, Bugwood.org) (d) life-cycle(http://asianlonghornedbeetle.com/spot-it/ )

Brown mulberry longhorn beetle

Brown mulberry longhorn beetle (Aprona germari,BMLB) is a polyphagus wood-boring insect, recorded as feeding on 65 known host plants, including a large number of hardwood trees such as apple, elm, fig, mulberry, poplar, pear, citrus, rosewood, hawthorn, lagerstroemia, mulberry, walnut, and willow (CABI, 2014).  BMLB occurs naturally in the Asian region, including Myanmar, China, Japan, Korea, Indochina (Vietnam, Laos and Cambodia), Malaysia, West Pakistan, North India, Taiwan, Thailand, and Nepal (NMA, 2010). It is reportedly a major pest of Morus spp., Populus spp., Pyrus spp. and Salix spp. with particularly severe damage in India and China on mulberry and poplar plantations (NMA, 2010, DA,2014, Huang, 1996 in Shui et al., 2009, Huang et al., 1994, Ma et al. 1997, Huang et al., 1997).Brown mulberry longhorn beetle is particularly damaging in arid situations (Ji et al., 2011).The potential impact of brown mulberry longhorn beetle on Australian native plants is not known.

An adult beetle is large being about 26 to 50 mm long. Its body is black and covered with tawny brown to slightly greenish hairs (Figure 4). The antennae are brownish black with whitish grey rings and can be up to one third longer than the body.

BMLB attacks only living trees. Like other longhorn beetles, brown mulberry longhorn adults lay eggs under the bark on host trees. The eggs are about 8 to 9 mm long, with a brown tinge and are laid in slits made in the bark by the female adult beetle. After eggs hatch, the developing larvae feed under the bark forming tunnels or “galleries”. Later larval stages also bore into the woody tissue and can grow up to 70 mm long. Over time, the feeding activity of the larvae can cause a decline in the health of trees and ultimately death.

Figure 4. Adult brown mulberry longhorn beetles(http://www.timesofmalta.com/articles/view/20121031/environment/An-unfriendly-squeaking-beetle.443379)( http://sinobug.aminus3.com/image/2011-08-01.html).

Japanese Pine Sawyer Beetle / Pine Wilt Nematode

The genus Monochamus contains several species of cerambycid beetles commonly known as longhorn beetles or pine sawyer beetles, which are native to temperate regions of North America, Asia, Africa and Europe. Adult pine sawyer beetles are secondary invaders of recently cut timber and felled, stressed, dying or dead coniferous trees. While they damage freshly cut timber by feeding and creating tunnels in the wood, Monochamus spp. in their own right are not generally considered to be serious forest pests. Their significance as a pest lies primarily due to their role as a vector of the pine wilt nematodeBursaphelenchus xylophilus, the causal agent of pine wilt disease. The beetle carries the nematode from an infested tree to a new host tree either when it feeds on the bark and phloem of twigs of susceptible live trees, or when the female beetle lays eggs (oviposits) in freshly cut timber or dying trees (Plant Health Australia 2007).

Pinewood nematodes, and in particular Bursaphelenchus xylophilus, are members of the pinewood nematode species complex (PWNSC) that are associated with pine wilt disease. Pine wilt disease manifests as a rapid wilt of susceptible pine species and causes extensive mortality in softwood plantations and forest environments(Figure 5). Bursaphelenchus xylophilusis pathogenic on a number of pines, as well as larch, spruce and fir. While other species of Bursaphelenchus have also been associated with death of pines, many are thought to be saprophytic.

Bursaphelenchus xylophilusis native to North America. It is an introduced pest in China, Japan, South Korea, Taiwan and Portugal where it has caused extensive mortality in pine plantations and forests. (Plant Health Australia, 2007). The likely pathway into Australia is via insect vectors introduced in bark, lumber and wood packaging material including dunnage.

Figure 5. (a) Pine wood nematode (L.D. Dwinell, USDA Forest Service, Bugwood.org), (b) damage and (c& d) Monochamus beetle vector (Christopher Pierce, USDA APHIS PPQ, Bugwood.org).

Detection of longhorn beetles in Australia 2014.

In early 2014, the Department of Agriculture investigated consignments of timber pallets imported from China that were associated with non-timber building material (Figure 6). Some of the timber pallets were found to contain exotic timber pests.The pests of biosecurity concern included the Asian longhorn beetle, the Brown Mulberry longhorn beetle and the Japanese sawyer beetle. Nematodes species were also detected in one of the Japanese sawyer beetles (DA 2014).

These beetles could cause serious damage to our forestry industry, natural environment and urban parks and gardens. Ongoing surveillance continues to demonstrate that the beetles were confined to the immediate site of the infestation and have not entered the environment. To date no evidence that any of the beetles or nematode species have become established in Australia.All infested pallets were fumigated and tracing activities were used to account for all timber pallets imported.  Fumigation kills any beetles present, as well as any eggs, larvae or pupae inside the timber.

Figure 6. Timber pallet showing damage and longhorn larvae in situ and galleries within the wood (DA 2014)

Future threats

Dutch Elm Disease

Dutch elm disease (DED) is one of the most serious threats to elms within Australia. DED has killed tens of millions of elms in Europe and North America over the past 50 years. It is caused by the fungal pathogen Ophiostoma ulmi that infects and grows through the water conducting system of elm trees blocking the flow of water.  Symptoms of DED include yellowing, curling, wilting, death of leaves (flagging) and brown longitudinal streaks in the sapwood of infected branches (Figure 7).  The pathogen can be vectored from tree to tree through spores adhering to Elm bark beetles(Figure 7),and infects through wounds created during their feeding within the branches. The fungus can then spread through the branches into the main trunk and root systems of a tree and infect other trees in close proximity through root grafting.

One of the bark beetle vectors of the pathogen is the smaller European elm bark beetle (Scolytus multistriatus) This beetle vector is already well established in Australia, and could rapidly spread the fungus throughout the elm population. The detection of the disease in New Zealand in 1989 is of particular concern to Australia due to its geographic proximity to Australia and their inability to eradicate the pathogen (http://www.biosecurity.govt.nz/pests/dutch-elm-disease). While eradication was unsuccessful, the containment program initiated through the removal of all known infected trees reduces the possibility of an infected beetle accidentally being introduced to Australia. In 2012, about 50 elm trees were removed due to a DED outbreak on private properties in the Whitford area of Auckland.

A National DED contingency plan has been developed and includes pre-introduction measures to reduce the impact of the pathogen should it be introduced. This includes a surveillance program to pick up early symptoms of disease, improvement in the current health of elmsand removal of any unwanted elms so as to reduce potential beetle breeding sites.

Figure 7. Dutch elm disease symptoms in USA including (a) flagging (Petr Kapitola, State Phytosanitary Administration, Bugwood.org), (b) streaking in wood (North Carolina Forest Service Archive, Bugwood.org),(c) galleries of beetle vector (Beat Forster, Swiss Federal Institute for Forest, Snow and Landscape Research, Bugwood.org)and (d) adult beetle vectorScolytus multistriatus (Pest and Diseases Image Library, Bugwood.org)

Asian gypsy moth

Asian gypsy moth (AGM) (Lymantria dispar (Linnaeus)) is an exotic lepidopterous defoliating pest that is native to the Russian Far East and is found throughout China, Korea, Japan, as well as being detected in the United States, Canada and New Zealand (Pitt et al. 2007). AGM underwent a successful eradication program in New Zealand.

AGM is one of the most significant exotic insect pest species of concern to Australia as it has an extensive host range (over 650 tree and plant species), enabling the potential for rapid establishment and long distance spread. It poses a significant threat to commercial and native forests, parklands and trees in other public use areas. Examples of trees at risk in the moth’s larval phase include pine, apples, oaks, elms, cherries, acacias and eucalypts. Feeding trials have indicated that important commercial and amenity species including Corymbia maculata, Pinus radiata, Eucalyptus grandis and E.camaldulensis are at potential risk from AGM defoliation (Matsuki et al. 2000,Commonwealth of Australia, 2001).In North America, gypsy moth (European form) has caused considerable damage to several important tree species in the 120 years since its initial introduction (Figure 8a). While single defoliations do not usually result in tree mortality, repeated events have the potential to severely weaken trees leading to eventual death.

Adult moths (Figure 8c) emerge in summer where they mate, with the females laying egg masses on tree bark, cliff faces or on infrastructure such as metal containers and ships superstructure (Canadian Food Inspection Agency 2006). The eggs hatch and the larvae (Figure 8b)that emerge form a fine silken thread that may be picked up on the wind allowing the tiny larvae to spread to new potential hosts. Larvae grow as they consume foliage prior to pupating and recommencing the lifecycle as an adult.

Since 1980, the US has spent in excess of US$30 million annually on gypsy moth control with a further US$34 million spent so far on an eradication of an AGM incursion from Russia (Matsuki et al. 2000). In the 1990’s, incursions of the European and Asian forms (including hybrids of both race) have been intercepted along the east coast of the United States and over the past 25 years, repeated incursions of the Asian form have been detected along the west coast of Canada and the United States. Although these incursions have not led to establishment, they indicate the ongoing detection and eradication effort required over sometimes prolonged periods to ensure areas remain pest free. In early 2002, quarantine inspectors at the Port of Brisbane intercepted an AGM egg mass on machinery imported from Japan. While in March 2003, an adult female AGM was trapped in Hamilton, New Zealand resulting in an extensive monitoring and eradication program in late 2003 at an estimated cost of $11 million. As part of a Federal Government initiative in 1996, monitoring traps were located at major shipping ports around Australia as these were considered the most likely point of entry for AGM. The program serves as an ‘early warning system’ to detect and identify incursions of exotic Lymantrid species entering through Australian ports.

Figure 8. Asian Gypsy Moth (a) defoliation (Robinson,M.E. – USDA Forest Service), (b) caterpillars (Ghent,2014) and (c) adults (USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org)

Sentinel Tree Plantings

Sentinel tree plantings are a monitoring and surveillance technique that uses specific tree species to keep watch for anticipated pest events either within the country of potential threat, or in the country of the pest’s origin.  Thus there are two main uses of sentinel tree plantings:

Post-Border surveillance:

Tree species known to be susceptible to exotic pests may be planted surrounding high hazard sites (e.g. ports and their environs), to provide early detection of pests entering a country.  Trees already established in gardens surrounding hazard sites may also be used (e.g. as with the Williams town Botanic Gardens for detection of pine nematode). It is important in quarantine biosecurity situations such as with pine nematode, that the local flora be well sited, described and monitored. Established and well-mapped trees across a city may also be used in the response phase of an incursion to rapidly survey the spread and extent of an incursion. The monitoring may be as simple as arranging for regular and routine reporting of damage by botanic garden, council and professional arborists.

Pre-Border surveillance:

Tree species of unknown susceptibility may be planted and monitored in an exotic region to assess the potential that native pests of that region may have to the species under investigation. For example Australian native species may be planted amongst native forest in North America to assess the potential of North American pests (both native and established exotics), to Australia’s forests. Existing gardens and arboreta may also be used for this purpose.  For example the extensive arboretum of Australian native species planted in Santa Cruz in California (UC Santa Cruz), could provide an opportunity to monitor for potential exotic pests to Australia. These plantings were used to assess Australian tree species for their susceptibility to Phytophthora ramorum (Ireland et al. 2012a & b).  In this manner the susceptibility of the different tree species can be determined, and potential pathways for their introduction closed and/or monitored.Alternatively the extensive planting of eucalypts across the world if monitored,could provide Australian authorities with an early warning of potential new incursions (e.g. Eucalypt rust in South America).Conversely, Australia’s extensive plantings of exotic trees can equally provide an important early warning system for countries of their origin,should Australian species become pests.Individual countries could enter into agreements to monitor and report on the trees on their behalf. The monitoring may be as simple as arranging for regular and routine reporting of damage by botanic garden, council and professional arborists, and thecurrent forest health surveillance activities carried out in each State.

In developing a sentinel plant network for the production of an early warning system for exotic pests, it was identified that linking with local councils that maintain detailed Geographic Information System tree information around high risk areas such as Melbourne ports and airports, to be key to a quick response system. A pilot sentinel plant program has been with four Melbourne councils (City of Melbourne(COM), City of Port Phillip Council (COPP), Hobsons Bay City Council (HBCC) and Hume City Council (HCC)).  All councils are enthusiastic about the program and have provided their tree databases for examination.

During the program, known pest host interactions are examined to provide a list of the tree species that are at risk from the 24 exotic pests of known concern to Victorian Forestry.  This investigation required a thorough literature search that identified 77 tree genera and over 100 species of trees that are at risk from an exotic pest incursion. Tree databases around the Melbourne port and airport and the local councils were supplied in ArcGIS format (geo-reference database) and analysis of the COM tree data has been initially investigated to test its feasibility. Each tree within the databases has a latitude and longitude so tree distribution can be displayed.  The database provided by COM contains 49,818 trees with 55 genera.  Within these 55 genera there are over 100 tree species that are susceptible to the 24 exotic pests of concern.

The benefit of geo-referenced tree databases is that risk modelling that can be performed showing the distribution of the trees that are most at risk to a specific pest and maps produced quickly for incursion surveillance.  This strategy was tested in 2010 and again in 2014 when exotic pests were detected in Australia (as previously described).  The data enabled the Department of Environment and Primary Industries and Councils to analyse their risk and prioritize the emergency response. Tree data can also be used to prove area freedom.


Protection of our valuable urban trees and plant industries is a joint responsibility of government (Federal, State and Local), industry and the general public.  The increased number of pest interceptions with increased trade has highlighted the need for continued vigilance and support by tree management agencies, industry and the general public to detect those that may escape detection at border entry points.

The supply of geo-referenced tree databases by local councils to agencies responsible for surveillance activities, has greatly improved the ability to detect pests and rapidly respond to incursions. However, this is dependent on the maintenance of these databases, provision of good identification material and training of those who are at the front line of detection, and the allocation of sufficient resources to adequately cover detection and response activities.

This paper has highlighted the threats to urban trees in Australia from exotic pests, and the importance of early detection and a rapid response.

Reporting suspect pests

Any unusual plant pest should be reported immediately to the relevant state or territory agriculture agency through the Exotic Plant Pest Hotline (1800 084 881). Early reporting increases the chance of effective control and eradication.

Reporting an exotic plant pest should be done only via the Exotic Plant Pest Hotline. Careless use of information, particularly if a pest has not been confirmed, can result in extreme stress for individuals and communities, and possibly damaging and unwarranted trade restrictions.

If you suspect a new pest, call the Exotic Plant Pest Hotline

Calls to the Exotic Plant Pest Hotline will be forwarded to an experienced person in the department of agriculture from the state of origin of the call, who will ask some questions about what you have seen and may arrange to collect a sample. Every report will be taken seriously, checked out and treated confidentially.

In some states and territories, the Exotic Plant Pest Hotline only operates during business hours. Where this is the case, and calls are made out of hours, callers should leave a message and contact details and staff from the department of agriculture will return the call the following business day.

Suspect material should not generally be moved or collected without seeking advice from the relevant state/territory department, as incorrect handling of samples could spread the pest or render the samples unsuitable for diagnostic purposes. State/territory agriculture department officers will usually be responsible for sampling and identification of pests.


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