Science Media Centre

Science Media Centre

Posted in Expert Reactions

Get RSS of
Expert Reactions

Kauri dieback in the Waitakere Ranges — Expert Reaction

Posted in Expert Reactions on August 10th, 2017.

Auckland Council yesterday released a report stating that infection rates of kauri with dieback disease in the Waitakere Ranges Regional Park have more than doubled in the last five years.

The report shows that the number of kauri within the park has risen from 7.9% in 2011 (with a further 2.7% possibly infected) to 19.0% infected in 2016 (with a further 4.7% possibly infected).

Scientists say the best chance of preventing the spread of kauri dieback disease is compliance: use the cleaning stations, stay on track and don’t go in closed-off areas.

The SMC asked experts to comment on the report. Feel free to use these comments in your reporting.

Dr Nick Waipara, Principal Advisor for Biosecurity at Auckland Council, co-author of the report comments:

“The disease is mostly spread from soil movement. In our latest report, we confirmed something we’d seen in 2011 which was that almost 70% of the distribution [of the disease] in the park is within 50m of a track.”

“Most of this spread is from non-compliance — we know this from surveillance footage, track counters and staff. People aren’t using the spray-stations, they’re breaching closed areas and continuing to use closed tracks. By doing that, they are introducing the pathogen into areas where it wouldn’t have been introduced if they’d stayed out. In some places, 80% of track users are not using the spray, but the compliance is highly variable.”

“We’re heartbroken. But it shows a lack of knowledge, a lack of education: people are genuinely confused. Some people are sceptical that these hygiene stations, or track closures, or messages to stay on track are working.”

“We want to know what people think to help with compliance. We’ve got a big job to do to get awareness up. People don’t realise it’s actually people vectoring the disease and that everyday actions — a bit like turning out lightbulbs to reduce your energy footprint — actually do make a difference.”

Dr Maj Padamsee, mycologist, Landcare Research, comments:

“Kauri dieback, caused by Phytophthora agathidicida, is a soil-borne disease that is devastating our kauri trees. The report from Auckland Council shows that the rate of infection in the Waitakere Ranges Regional Park (WRRP) has doubled in the last five years bringing up the question of whether preventing all public access to the park is needed to protect the trees from continued spread of the disease.

“The main issue is that the pathogen cannot be eradicated once it is present in a particular area. The only possibility is to prevent the spread of the disease to unaffected kauri trees. The final recommendation of the report advocates an independent review to assess whether public access to WRRP should be restricted; the authors of the report are not implementing the prevention of public access but instead suggesting that this drastic step may be necessary if an independent review also finds it is the only way to prevent the continued spread of kauri dieback.

“In the immediate future, the tools that are available to prevent the spread of kauri dieback is avoiding the trees, adequate cleaning stations (and the willingness of people to use them), and the “band-aid” approach of phosphite injections. There are other research projects being conducted in preventing the spread but they are not ready to be implemented. What is needed is financial backing for fundamental research to understand kauri ecosystems and the disease as well as an intergenerational approach to keep kauri standing.”

How does kauri dieback spread?
“Kauri dieback is caused by Phytophthora agathidicida, which is a soil-borne pathogen. This disease produced infective propagules (or cells) that can move through wet soil to infect tree roots. Resting spores (another phase of this organism) can be spread by movement of soil. See here for the lifecycle of the disease.

The council report said the number of trees infected rose from 7.9% in 2011 to 19.0% infected in 2016. Is this surprising based on how the disease spreads?
“No. Since the disease-causing organism is spread through the soil, it can easily be moved from one place to another by people or animals or even water moving through the soil.”

Would the monitoring of these areas had an impact on spreading the disease?
“It is unlikely that the monitoring would have had an impact on spreading the disease as very strict hygiene procedures were followed when monitoring the different areas.”

There has been some success in using phosphite to halt the spread of the disease. Why does this only halt, but not kill the disease?
“Phosphite is a temporary solution (like a band-aid) to halting the spread of the disease. Trees have to be individually and repeatedly injected to halt the spread of the disease. It is not a cure for the disease.”

What are some other scientific methods that have shown promise/what other methods are being trialled?
“Kauri trees are being tested for resistance to kauri dieback. If such trees are found, then seeds from these trees can be used in reforestation efforts. There is a study looking at the (good) fungi inside of kauri roots to see if these could protect trees against the disease. There is also a study to look at other compounds that could stop the growth of the pathogen.”

How do the kauri protection zones work (and why they might have failed)
“Kauri protection zones work by stopping access to kauri trees that are vulnerable because of their proximity to tracks. If people disregard track closures, the protection zone would fail because of the soil movement. The other important piece of knowledge that is needed is an accurate map of infected and healthy kauri trees throughout their range to see where and how the disease can spread.”

Is the disease found overseas, and if so, what are the protection measures elsewhere?
“The disease has not been found overseas. However, many other countries have had to managePhytophthora diseases, such as Phytophthora dieback of Jarrah trees in Australia, Sudden Oak Death in the US, etc.”

Have there been any major successes in defeating plant pathogens in the past (either here or overseas)?

“Yes. There are many plant pathogens that have been managed successfully here and in other countries. However, there are also multiple instances of plants being lost due to plant pathogens. There are multiple types of plant pathogens from rust fungi to viruses. Each disease needs a different management or control strategy and a “one size fits all” approach cannot be used. You have to take into account the peculiarities of each pathogen to successfully control it. In the case of kauri dieback, we need to understand the pathogen, where is the pathogen found, and the ecology (including the microbes) of the tree. The different thing about fighting kauri dieback is that kauri are ancient trees that grow extremely slowly and thus have a very complex relationship with their ecosystem. Additionally they are extremely culturally important and so we must take a cautious approach to treating them and the disease. We want to make sure that kauri are still standing for generations to come. ”


Dr Monica Gerth, Biochemistry Research Fellow, University of Otago, comments:

How does kauri dieback spread?
“Human assisted spread of kauri dieback is the primary factor in New Zealand. P. agathidicida (the causative agent of kauri dieback) produces various spores that can be spread by animals moving from tree to tree, and by human activity. This is why people are advised to clean and disinfect their shoes whenever entering or leaving native forests and to avoid walking on kauri roots. It can also spread via zoospores, which swim through waterlogged soil and seek out kauri roots using chemotaxis (moving towards some chemical cue produced by kauri).”

Once infected, how long will a kauri tree take to die?
“It depends on the size and health of the tree – anywhere from days to years.”

The council report said the number of trees infected rose from 7.9% in 2011 to 19.0% infected in 2016  Is this surprising based on how the disease spreads?
“This is not surprising, given the ease with which P. agathidicida can spread. Resting spores produced by P. agathidicida can lie dormant in soil for months to years, waiting to be picked up by a person’s shoe and spread to a new host. Additionally, there is no cure for kauri dieback; phosphite is used to prevent the death of individual trees, but it does not eradicate the disease from the tree. So, until we can develop better control methods, the rate of infection can only go up.”

Would the monitoring of these areas had an impact on spreading the disease?
“The monitoring procedures are very unlikely to contribute to the spread of the disease. The researchers conducting the monitoring have incredibly strict phytosanitary procedures to avoid cross-contamination – these are people that are passionate about the health of kauri trees and our native bush.

“Members of the public going off-track, and/or not using the footwash stations (compliance has been measured to be as low as 20% in some areas) are much bigger problems at the moment!”

There has been some success in using phosphite to halt the spread of the disease. Why does this only halt, but not kill the disease? 
“Phosphite works in two ways. First, it directly inhibits the growth of P. agathidicida. In the laboratory, it can completely stop growth if used at a high enough concentration (though it is relatively poor compared to other chemicals).

“Second, it induces defense responses in the kauri itself, which helps the kauri tree to limit the infection. The problem, however, is that kauri’s phosphite-boosted ‘immune’ response isn’t enough to completely eradicate the disease, and high doses of phosphite, which might be used to directly kill P. agathidicida, appear to be toxic to kauri.”

What are some other scientific methods that have shown promise/what other methods are being trialled?
“Unfortunately there isn’t enough research funding in this space!  There is some great research by Dr. Amanda Black (Lincoln University) looking at how different soil types affect the spread of disease. In addition to this, with funding from the Biological Heritage National Science Challenge, my group is trying to figure out exactly how zoospores seek out their kauri hosts, and how we might be able to stop them from doing so. The Auckland Council has also been trialling the use of naturally occurring beneficial microbial antagonists of P agathidicida to mitigate root damage/infection. There are lots of good ideas out there – but we need more resources.

Is the disease found overseas, and if so, what are the protection measures elsewhere?
P. agathidicida is unique to New Zealand, and appears to only infect kauri. Its origins are unclear, but kauri dieback was first detected on Great Barrier Island in 1972, and has since spread throughout northern New Zealand. There are over 100 described species of Phytophthora worldwide, including at least 30 in New Zealand.

“A comparable disease to kauri dieback is sudden oak death, found in the USA and Europe and caused by P. ramorum. In the USA, the disease is treated similarly to kauri dieback: sanitation of shoes, vehicles etc and treatment of individual trees with phosphite. One major difference is that in the USA, infected (or likely to be infected) trees are removed to stop the spread of the disease. For example, in Oregon, all host trees within 90 metres of an infected tree are removed. This is obviously not an option for the few remaining kauri stands in New Zealand!”

Have there been any major successes in defeating plant pathogens in the past (either here or overseas)?
“There are success stories when it comes to plant pathogens, but these tend to be in commerically-important agricultural plants. For example, squash and papaya plants genetically modified to resist viral infection have been sold overseas for the last 20 years.

“In terms of Phytophthora diseases, total eradication is virtually impossible, but spot eradication has been successful for some species. For example, in Australia, P. cinnamomi (which infects avocado trees in New Zealand) has been successfully eradicated from plants and soil in small areas, but this required fumigation, fungicides and destruction of host plants.”

What about fighting kauri dieback is different?
“Phytophthora diseases are inherently difficult to treat for several reasons. While they resemble fungi, they are actually quite different biologically, meaning that many conventional antifungals and antibiotics are ineffective against them. They also have a complex life cycle and produce resting spores that can remain hidden in the soil for long periods of time. They can also spread remarkably quickly, either through human activity or by producing swimming zoospores (which can move through wet soil at up to half a metre per hour).

“Fighting kauri dieback is particularly difficult because kauri are a relatively rare and long-lived species, meaning that host removal is not an option and treatment options have to be carefully considered, bearing in mind the cultural and ecological significance of the trees and the surrounding environment.”

Does the suggestion to close the Waitakere Ranges to the public have a scientific basis?
“The report shows a close correlation with the Waitakere visitor track network, and the disease has continued to be detected in new areas particularly along the tracks.  The suggestion to close the Waitakere ranges makes sense given the current data — and the lack of a ‘cure’ for infected trees.”

Erik Van Eyndhoven, Principal Adviser Conservation, the Ministry for Primary Industries, comments:

How do the Kauri protection zones work? And why might they have failed?
“Kauri protection zones are areas containing healthy kauri where the disease has not been detected. The aim is to prevent human-assisted spread of kauri dieback into these areas.

“Thirteen protection zones were created by Auckland Council in an attempt to prevent disease introduction to approximately 400ha of kauri forest within the Waitakere Ranges Regional Park.

“However, Auckland Council’s Kauri Dieback Report 2017 does state that observations of feral pig activity, baitlines and off-track human activity has been recorded within four of the thirteen protection zones.

“The report also indicates that current results from monitoring human activity along the closed tracks with in the protection zones is showing that while visitor numbers have been reduced in some instances, overall the usage remains high.”

Does the suggestion to close the Waitakere Ranges to the public have scientific basis?
“As the disease is soil borne and is spread by soil movement between trees, people visiting affected areas are the biggest vector for spreading infected soil.

“If the Auckland Council in consultation with tangata whenua decided to close the Waitakere Ranges to the public, MPI would support this approach.”

The council report said the number of trees infected rose from 7.9% in 2011 to 19.0% infected in 2016. Is this surprising based on how the disease spreads?
“Given the pathogen is soil-borne and only a pinhead of soil is enough to spread the disease, the best way to reduce spread to other areas is to prevent the movement of infected soil. If members of the public are not adhering to our message of making sure they stay on track and clean their footwear before they enter and exit a kauri forest, then the disease will spread, no matter how much research you do or mitigation measures you put in place. Based on the report’s findings this seems to be the case with what’s happening at the Waitakere Ranges.”

There has been some success in using phosphite to halt the spread of the disease. Why does this only halt, but not kill the pathogen? 
“Phosphite works by boosting the plant’s own natural defences and thereby allowing susceptible kauri to fight the pathogen. It does not kill the pathogen directly.”

What are some other scientific methods that have shown promise and what other methods are being trialled?
“Apart from phosphite, we are also currently trialling a number of alternative treatments such as the use of natural products & biological control agents as well as looking into genetic resistance of kauri to the pathogen. We also plan to undertake research in the use of temperature to kill the disease as well as determining whether traditional Maori medicines can be effective.

“There are also a number of other research projects that are currently occurring such as (1) the use of remote sensing tools to detect kauri and the disease (2) determining whether dogs can detect the disease (3) using cultural health indicators in monitoring the health of kauri forests and disease impact (4) the creation of a geodatabase that informs abundance, composition, distribution, and maturity of kauri trees as well as the creation of additional GIS layers that informs the level of risk of a number of vector pathways.”

Is the disease found overseas, and if so, what are the protection measures elsewhere?
“At present, the disease is not known to occur overseas, it’s only in New Zealand.”

Have there been any major successes in defeating plant pathogens in the past (either here or overseas)?
“The pathogen that causes the disease is called Phytophthora agathidicida. The genus Phytophthora are difficult to control and countless overseas studies have indicated that it is virtually impossible to completely eradicate this group of pathogens from a natural ecosystem. The best way is to have an integrated approach to reduce the spread of the disease and hence its impacts on kauri.”

Dr Cate Macinnis-Ng, plant ecologist, University of Auckland, comments:

“This report is very distressing to read. The Waitakere Ranges are a national treasure yet they have the worst concentration of kauri dieback in the country. There has clearly been a substantial increase in the numbers of infected kauri over the last five years and this tells us the current measures to protect kauri are not effective.

“Kauri dieback is spread when the microscopic pathogen that causes the infection is spread in soil. The high concentration of infected trees close to tracks compared to lower rates in less accessible parts of the regional park indicates that human activities are the most likely factor spreading infected soil.

“There are two issues that need to be addressed here. First, it is vital that people entering the park scrub their boots and other equipment to remove soil before and after entering areas with kauri in them. This is particularly important at this time of year when the tracks are thick with sticky mud. Usage rates of cleaning stations are quite low on some tracks. We all need to take responsibility for cleaning.

“The second issue has to do with the design of the cleaning stations. The report indicates that some of the cleaning stations are not fit for purpose. Contaminated soil isn’t properly removed from the track. The new cleaning station at Tane Mahuta is designed in such a way that it is impossible to enter the track without going through the easy to use and highly effective cleaning system. We need more robust cleaning stations like these on all tracks.

“If these two measures are not implemented quickly, we will lose more trees to this horrible disease, so we need to start thinking about other approaches to protect the forest. Mana whenua have been advocating for a rahui (exclusion zone) for some time. By keeping people out of an area, there is potential to decrease the spread of the kauri dieback, buying time to find treatments and breed resistant trees.

“Enforcing an exclusion zone would be challenging in an area so close to a large city but they are used elsewhere in the world to conserve special areas. For instance, the NSW National Parks and Wildlife Service has ‘wilderness areas’ that are pristine environments or contain sites of cultural significance to Aboriginal people. These areas have restricted access but are often in remote places.

“There is never going to be a quick-fix for kauri dieback. The report doesn’t mention the size or age of trees that are dying but without doubt, some of the trees will be centuries old. Even if we found a cure tomorrow (highly unlikely), these trees will not be replaced in our life time, our children’s lifetime or even our grandchildren’s lifetime. Auckland Botanic Gardens, Auckland Council and MPI are to be commended for this important research, but we need to be working faster and smarter on this. We need more money for fundamental research and to find treatments.

“Until that happens, people need to clean, clean, clean and stick to the tracks.”

Print Friendly, PDF & Email
Copyright 2017 Science Media Centre (New Zealand)

Disclaimer | Privacy Policy