Pre- and post-border biosecurity New Zealand Plant Protection 68: 66-75 2015

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Pre- and post-border biosecurity

New Zealand Plant Protection 68: 66-75 (2015


D.A.J. Teulon


, T.T. Alipia


, H.T. Ropata


, J.M. Green


, S.L.H. Viljanen-



, M.G. Cromey


, K. Arthur


, R.M. MacDiarmid


, N.W. Waipara



A.T. Marsh



The New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, 

Christchurch 8140, New Zealand


The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, 

Auckland, New Zealand


Auckland Council, Bledisloe House, Aotea Square, Private Bag 92300, Auckland 


The New Zealand Institute for Plant & Food Research Limited, Private Bag 11600,  

Palmerston North, New Zealand


Better Border Biosecurity (B3), New Zealand (

Corresponding author:

Abstract Myrtle rust, caused by the pathogen Puccinia psidii, is a disease of plants in the 

Myrtaceae that is currently not known to be present in New Zealand. Its origin is Central/

South America, but it has steadily spread around the world and is now found in Australia. 

All New Zealand Myrtaceae species, including indigenous species, are at risk from myrtle 

rust infection, but the extent of the impact on plant health is not known. While the potential 

economic and environmental impacts of myrtle rust establishment in New Zealand have 

been well documented, this paper explores potential socio-cultural consequences for Māori. 

All indigenous Myrtaceae species can be considered as taonga (or treasure) by Māori, who 

have and continue to use the properties of some species in many ways (both tangible and 

intangible). Preparedness and response plans for a myrtle rust incursion in New Zealand 

should consider the values that Māori derive from these plants.

Keywords myrtle rust, Puccinia psidii, Māori, taonga species, Myrtaceae.

The threat of myrtle rust to Māori taonga plant species 

in New Zealand


There is considerable concern about the likely 

arrival, establishment and impact of myrtle rust 

on introduced and indigenous plant species of the 

Myrtaceae in New Zealand (Clark 2011). Myrtle 

rust, caused by the pathogen Puccinia psidii in 

the Order Pucciniales, is a disease of many plants 

belonging to the Myrtaceae. Its origin is thought to 

be Central and South America (Glen et al. 2007), 

but it has been steadily moving around the world 

in recent years and is now found in New Zealand’s 

close neighbours, Australia (including recently 

Tasmania) and New Caledonia (CABI 2014).

Clark (2011) provided a comprehensive 

review of the taxonomy, biology, host range and 

plant associations, geographic distribution, risk 

of entry, spread and establishment for P. psidii 

into New Zealand and its potential economic 

and environmental impact. In summary, she 

concluded that there is a high likelihood of arrival 

of entry to New Zealand and subsequent climate 

© 2015 New Zealand Plant Protection Society (Inc.)     Refer to


Pre- and post-border biosecurity

modelling identified that much of the North 

Island and a very small area in the north of the 

South Island are climatically suitable for P. psidii 

(Kriticos et al. 2013; Narouei Khandan 2014). 

Clark (2011) identified variable economic and 

environmental impacts and recognised moderate 

to high potential socio-cultural consequences 

for all New Zealanders. However, the socio-

cultural consequences for Māori have not been 

explored in any detail. Similarly, Loope (2010), 

in summarising the risk of additional strains of  

P. psidii to Hawai’i, provided only a short 

paragraph on the threat to Hawai’ian indigenous 

culture. There appears to be no comment in 

the literature on the the impact of P. psidii to 

Australian Aboriginal communities and culture.

The flora and fauna of the bush are taonga 

(or treasure) species and the Māori relationship 

with them is one of kaitiakitanga (guardianship); 

this relationship is multifaceted and intimate, 

developing over more than 40 generations 

(Waitangi Tribunal 2011). Taonga species may be 

part of a defined list (e.g. DOC 2006) or more 

generally any species of importance to Māori, 

and may include both indigenous and non-

indigenous species (e.g. kūmara, taro, kiore, 

wild pig) (Roberts 2009). The WAI 262 claim Ko 

Aotearoa Tēnei (This is Aotearoa or This is New 

Zealand) (Waitangi Tribunal 2011) informs us 

that “iwi have relationships with species which 

are emblematic and have a spiritual element to 

them and their connection to the wider ecosystem 

particularly with regard to native plants such 

as harakeke, koromiko, pōhutukawa, kōwhai, 

puawānanga, poroporo, kawakawa, mānuka 

and kūmara” (Katene 2011). Taonga include 

tangible things such as land, waters, plants, 

wildlife and cultural works, and intangible things 

such as language, identity and culture, including 

Mātauranga Māori (the Māori way of viewing the 

world) (Waitangi Tribunal 2011). 

This paper provides information on the 

invasive biology of myrtle rust, a list the 

indigenous Myrtaceae found in New Zealand, and 

a summary of the modest amount of information 

known about P. psidii infection for these New 

Zealand species. The Māori uses, values and 

relationships of these species is explored and the 

possible impact of myrtle rust considered in this 

context if myrtle rust was to become established 

in New Zealand.


Myrtle rust (also known as guava rust, eucalyptus 

rust and ōhi’a rust) was first described from 

Psidium guajava (native guava) in Brazil (Winter 

1884). The native range of myrtle rust was 

reported to be South and Central America and 

the Caribbean (Coutinho et al. 1998; Silva et al. 

2013). In the 1970s, the pathogen caused severe 

damage in nurseries and eucalyptus plantations 

in Brazil (Coutinho et al. 1998). The literature 

reports numerous strains of P. psidii that have 

differential ability to infect different suites of host 

plants (Loope 2010). It is considered that there 

is only a single strain in Australia (Carnegie & 

Cooper 2011). Like many rusts, myrtle rust has 

a complex life cycle (Glen et al.  2007), which 

needs to be understood for the development of 

effective contingency plans for readiness and 

response to potential incursions. The spores are 

easily dispersed and can remain viable in the 

environment for several weeks (Clark 2011).

Since the 2000s, P. psidii has steadily 

spread around the world and is now found in 

Australia (including Tasmania) (Carnegie et 

al. 2010), South Africa (Roux et al. 2013) and 

New Caledonia (CABI 2014). Currently, 346 

species from 57 genera (73 worldwide) from 

the Myrtaceae are reported to be susceptible to 

myrtle rust in Australia and elsewhere (Giblin & 

Carnegie 2014a,b). 

Myrtle rust attacks young, actively growing 

leaves, shoots, fruits and flowers (Glen et al. 

2007). Leaves and stems become deformed and 

in severe infections growing tips (Coutinho et 

al. 1998) and the whole plants (Uchida & Loope 

2009) can die. Previous rust infection can also 

result in defoliation and prolific branching and 

galling. Floral buds and fruits can also be affected, 

with subsequent impacts on nectar production 

and reproduction (Glen et al. 2007). 

Puccinia psidii effects can be variable. It 

is rarely severe on native Central and South 

© 2015 New Zealand Plant Protection Society (Inc.)     Refer to


Pre- and post-border biosecurity

American flora, although can cause occasional 

epidemics on native guava plantations (Ribeiro 

& Pommer 2004). Similarly, over a period of 30 

years, this rust has done little damage to any of 

the scattered native Myrtaceae in Florida (Loope 

2010). Florida’s native Myrtaceae are among the 

roughly 1,100 neotropical species that are largely 

resistant to P. psidii but the 3,000 species of non-

neotropical Myrtaceae of the Pacific, Australia, 

Asia and Africa are expected to prove much more 

vulnerable to P. psidii (Loope 2010). In Hawai’i, 

crown dieback and complete tree death was 

recorded at a landscape scale from stands of the 

non-native Syzigyium jambos (Uchida & Loope 

2009) and the damage to Eugenia koolauensis, a 

federally listed endangered species, is of major 

concern (Loope 2010).  The impact of P. psidii 

on individual trees and shrubs in Australia has 

ranged from minor leaf spots, foliage, stem and 

branch dieback to reduced fecundity. Tree death, 

as a result of repeated infection, has been recorded 

for  Rhodomyrtus psidioides. The full impact of 

this disease in Australia may not be realized for 

some years (Pegg et al. 2014). Puccinia psidii is 

currently not causing serious disease in eucalypt 

plantations in Australia (Carnegie 2015). 



In New Zealand the Myrtaceae is represented 

by some of our best-known native plants 

such as the iconic pōhutukawa (Metrosideros 

excelsa), rata (Metrosideros diffusa), kanuka 

(Kunzea  spp.) and manuka (Leptospermum 

scoparium), as well as lesser-known species such 

as swamp maire (Syzygium maire) and ramarama 

(Lophomyrtus bullata) (Clark 2011), and species 

that are considered nationally critical, such as 

Metrosideros bartlettii, with only 29 individuals 

left in the wild (De Lange et al. 2004). The 

Flora of New Zealand database (Landcare 

Research 2015) lists 29 indigenous taxa from the 

Myrtaceae, 27 of which are endemic. De Lange 

(2014a) has recently increased the number of 

New Zealand indigenous Kunzea species to ten, 

further increasing the number of indigenous 

Myrtaceae. New Zealand also has a large number 

of exotic Myrtaceae species, many of which have 

commercial value, such as Eucalyptus  species 

and feijoa (Acca sellowiana (O. Berg.)), and some 

myrtaceous species that grow in New Zealand are 

weeds (e.g. Syzygium smithii) (Clark 2011).

All myrtaceous species (introduced and 

indigenous) found in New Zealand are considered 

to be potential hosts for myrtle rust. Some, 

mostly introduced plant species, found in New 

Zealand are known hosts for myrtle rust overseas 

(Giblin & Carnegie 2014a,b). Nine New Zealand 

indigenous species from four genera are known 

to be susceptible to myrtle rust from observations 

made on these plant species in the laboratory 

and in the field in Australia and Hawai’i (Table 

1). In addition, numerous non-New Zealand 

species from the genera found in New Zealand 

(including  Syzgium) have been recorded as 

myrtle rust hosts (Giblin & Carnegie 2014a,b), 

but little is known about the potential degree 

of susceptibility of New Zealand myrtaceous 

species. All species (including some New 

Zealand indigenous species) listed as myrtle rust 

hosts in New South Wales are considered to be 

susceptible to severe infestation under conducive 

conditions (Anonymous 2012). Loope (2010) 

reported that a few inviduals of pōhutukawa in 

the Lyon Arboretum in Hawai’i were seriously 

damaged by myrtle rust. Even though all New 

Zealand plant species from the Myrtaceae are 

at risk from myrtle rust it is not known which 

myrtaceous species will be susceptible, or how 

susceptible they will be.


A number of New Zealand’s Myrtaceae species 

were extensively used by Māori, including 

for medicine, construction and food, or have 

significant cultural value as summarized 

in Appendix 1 (collated by Scheele 2014). 

Information on the current use of these plants by 

Māori is likely to be iwi- and hapu-specific and 

difficult to obtain and catalogue (Scheele 2014).

A number of plant species from the Myrtaceae 

have been explicitly identified as taonga species 

(e.g. DOC 2006; Waitangi Tribunal 2011), in 

particular, the importance of pōhutukawa and 

mānuka to Māori (the WAI 262 claim; Waitangi 

Tribunal 2011). 

© 2015 New Zealand Plant Protection Society (Inc.)     Refer to


Pre- and post-border biosecurity

Pōhutukawa (New Zealand Christmas tree) 

is one of New Zealand’s most widely recognised 

trees, with brilliant red flowers and is a treasured 

ornamental plant. Pōhutukawa’s deep-red wood 

is exceptionally strong (Metrosideros means ‘iron 

hearted’) with various uses (Appendix 1). The 

flower nectar and bark preparations were used for 

various medicinal purposes (Appendix 1). Pale 

cream-coloured pōhutukawa honey is produced 

commercially. Pōhutukawa also has significant 

cultural and spiritual value to Māori. A specific 

named tree, Te Rēinga (older than 800 years), 

found on a cliff face at Te Rerenga Wairua (Cape 

Rēinga), has a central place in Māori tradition 

as it is said to guard the entrance to the sacred 

cave through which spirits pass on their way to 

the next world (Hawaiki). Another significant 

pōhutukawa is Karewa, in Kawhia Harbour, said 

to be the tree to which the Tainui waka was tied 

after completing its voyage across the Pacific from 

Hawaiki (Waitangi Tribunal 2011). At least 350 

years old, Te Waha o Rerekohu, at Te Araroa, near 

the East Cape, is probably New Zealand’s largest 

pōhutukawa (19.8 m high × 38.5 m wide). The 

pōhutukawa is the subject of numerous stories. 

Perhaps the best-known tells of the young warrior, 

Tawhaki, and his attempt to find help in heaven 

to avenge his father’s death. The pōhutukawa’s 

flowers are said to represent Tawhaki’s blood, shed 

after he fell to earth. There are numerous stories 

and pepeha (sayings) that tell of the relationship 

between the blooms of the pōhutukawa and the 

plume of red feathers worn as a headdress by the 

Hawaiikian voyagers (Waitangi Tribunal 2011). 

Mānuka (tea tree) is one of New Zealand’s 

most common native trees and Māori use of this 

tree has been extensive (Appendix 1). Mānuka 

wood has been used for firewood, a range of 

tools, building materials and weapons. Leaf and 

bark preparations were used for a wide variety 

of medicinal purposes (Waitangi Tribunal 

2011). Today, mānuka oil is recognised for its 

antibacterial, antifungal and antihistamine 

properties, and is used to treat a number of 

conditions. Mānuka honey is used as a general 

tonic, in wound-care products and in cosmetic 

skincare products. In 2014, New Zealand 

honey exports had a total value of $NZ186.6M 

(Fresh Facts 2014), mostly due to the premium 

price achieved by mānuka honey, which is 

approximately three times higher than that of 

other table honey (Coriolis 2012). 

Table 1 Records of myrtle rust (caused by Puccinia psidii) from New Zealand indigenous plant species. 

Sources: All Australian records are from Giblin & Carnegie (2014a), except for Lophomyrtus obcordata, 

which is from P. Symes (Royal Botanic Gardens, Melbourne, Australia, personal communication). All 

Hawai’ian records are from Loope (2010). There are no additional records of New Zealand indigenous 

plant species being infected by myrtle rust from the rest of the world (Giblin & Carnegie 2014b).

Host taxa

Natural infection = wild, open cultivation 

or greenlife industry


inoculation test

Kunzea ericoides



Leptospermum scoparium


Lophomyrtus bullata

Aust: NSW


Lophomyrtus × ralphii

Aust: NSW& Vic

Lophomyrtus obcordata

Aust: Vic

Metrosideros carminea

Aust: Vic

Metrosiderus excelsa

Aust: NSW & Vic, Hawai’i


Metrosiderus kermadecensis

Aust: Qld & NSW, Hawai’i

Metrosideros thomasii 

Aust: Qld


De Lange (2014a) has recently increased the number of New Zealand indigenous Kunzea species to ten, 

so it is unclear which species is referred to here. 


Abbreviations: Aust=Australia, NSW=New South Wales, Vic=Victoria, Qld=Queensland. 

© 2015 New Zealand Plant Protection Society (Inc.)     Refer to


Pre- and post-border biosecurity



Australia seems the most likely source for a New 

Zealand myrtle rust incursion as it it one of our 

major trading partners and the source of many 

of our tourists. Rust spores are easily carried 

on clothing and this pathway is a very likely 

source of accidental introduction to new areas. 

Additionally, a range of fungal rusts are thought 

to have arrived in New Zealand from Australia 

through prevailing westerly wind currents (Kim 

& Beresford 2008; Viljanen-Rollinson & Cromey 

2002). Therefore all New Zealand myrtaceous 

genera and species are expected to be at risk 

because the Australian biotype has a particularly 

wide host range (see above). Currently, MPI has 

suspended imports of cut flowers and foliage 

from Australian states where P. psidii is present 

(Queensland, New South Wales, Victoria and 

Tasmania; to prevent 

their entry into New Zealand. Once established 

myrtle rust is likely to spread quickly throughout 

New Zealand at least in the North Island. Climate 

matching models suggest that myrtle rust will have 

the greatest impact in the North Island (Kriticos 

et al. 2013, Narouei Khandan 2014) and species 

found predominantly in the South Island, such as 

southern rata (Metrosideros umbellata), may be 

at reduced risk. Which particular New Zealand 

genera and species will be most susceptible to 

myrtle rust is unknown, but greater information 

gathered from New Zealand native species grown 

in Australia (and possibly Hawai’i), especially 

from similar climates, may provide some clues, 

especially on their relative susceptibility.

Potential impacts of myrtle rust are likely to be 

variable. It mostly affects young plants and young 

tissues including flowers, and although tree death 

has been reported it is not the norm (Pegg et al. 

2014). Thus individual rakau rangatira (chiefly 

trees) such Te Rēinga, Te Waha o Rerekohu and 

Karewa are unlikely to be killed. However, their 

outward appearance, especially during periods 

of bud growth and flowering, might be affected. 

Similarly, uses of pōhutukawa and mānuka 

timber for construction and tools may not be too 

seriously affected; impacts on long-lived trees 

species, such as pōhutukawa, will be less obvious 

in the short term but may be significant in the 

long term. There are also likely to be intangible 

impacts because of the close relationship between 

Māori in their role as kaitiaki of taonga species, 

and for smaller Maori groups who have close 

connections to individual rakau rangatira, which 

have a central role in various pepeha and stories. 

Future regeneration may be at risk as a result of 

increased seed and seedling mortality during severe 

infestations, as has been reported for R. psidioides in 

Australia (Pegg et al. 2014). This may be especially 

apparent for species such as kānuka and mānuka, 

which are important in the development of early 

successional plant communities.

Loss of flowers and new growth has a 

number of potentially significant implications. 

Honey production for both pōhutukawa and 

mānuka may be significantly affected in terms 

of both productivity and quality. Similarly, the 

quality of medicinal (traditional/rongoa and 

modern) products from key species may also 

be compromised. Impacts in this area may very 

much depend on which elite honey and medicinal 

plant biotypes are affected by myrtle rust. 


Two summer students have been hosted by Better 

Border Biosecurity/Plant & Food Research to 

explore the potential impact of myrtle rust on 

plant species of interest to Māori. Alipia (2014) 

focussed more on the invasive biology of myrtle 

rust and its potential impact on New Zealand plant 

species whereas Ropata (2015) focussed more on 

engagement with Māori communities and their 

views of myrtle rust and its potential impact on 

plant species of interest to them. In particular, 

Ropata (2015) developed a focus group facilitated 

discussion process that was trialled with two 

Māori students (summer and post-graduate), 

one Māori scientist and one Māori support staff 

(total n=4) at Plant & Food Research in February 

2015 to understand their knowledge of myrtle 

rust, which taonga plant species were important 

to them, and why and how they would like to be 

involved in an incursion response (Ropata 2015). 

While the makeup of this group was small and 

© 2015 New Zealand Plant Protection Society (Inc.)     Refer to


Pre- and post-border biosecurity

probably not representative of the wider Māori 

community it did provide some insights into some 

of the potential concerns that Māori have over 

myrtle rust. Other commentators have indicated a 

strong interest by Māori in biosecurity issues, e.g. 

Flavell (2010).

One issue that clearly emerged from this 

preliminary engagement was that Māori 

communities and iwi authorities would very 

much like, and prioritise, is early involvement 

in the preparedness and response to myrtle rust 

(Ropata 2015). A tāngata whenua (local people) 

rōpū (group) was established in response to 

the discovery of kauri dieback and a similar 

partnership approach would provide strategic 

insight and knowledge (mātauranga Māori) for 

managing any myrtle rust incursions. Given the 

threat and likelihood of myrtle rust incursion, an 

early engagement approach to establish ongoing 

interactions between practitioners of kaitiakitanga 

(environmental stewards, guardians) and tāngata 

whenua groups, land managers and research 

scientists should be initiated. This approach 

would enable the implementation of mahi (work) 

to survey, catalogue and monitor sentinel plants 

for their growth and health status. Tāngata 

whenua are very familiar with their land and any 

taonga species plants that are present in their 

rohe (area), and can provide the local knowledge 

and expertise for any surveys and cataloguing 

of sentinel plants for their growth and health 

status, or lack thereof, over time and space. This 

knowledge and sentinel plant data could feed 

into a larger repository of information that could 

serve as a national network of plant health status. 

Collectively, this nationwide sentinel network 

may also form an ara (pathway) for two-way 

knowledge exchange, resulting in increased 

preparedness for a myrtle rust incursion and an 

early and successful response. 

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