Kauri PTA (kauri dieback) disease
Dr Stanley Bellgard heads Landcare Research’s research programme on PTA (kauri dieback). He stresses the importance of sensible plant hygiene practices and the protection of the kauri tree’s sensitive root environment to control the disease. He provides a summary of what is known about PTA and how it is being managed.
The genus Agathis (Araucariaceae) includes about 13 species of tropical to warm temperate trees found from Melanesia through Australia to New Zealand. Kauri (Agathis australis) is found in lowland forests in northern New Zealand. Giant individual trees, which can reach over 4.5 m in trunk diameter and exceed 1000 years of age, are cultural icons.
In 1972 sick and dying kauri trees were discovered in a forest stand on Great Barrier Island. This phenomenon came to be called “kauri dieback”. Early research concluded that a Phytophthora pathogen
(a disease-causing agent) was involved. Recent research has identified the Phytophthora as a distinct and previously undescribed species, now commonly known as PTA (Phytophthora taxon Agathis). PTA is a tiny, fungus-like (water-mould), plant pathogen that only affects kauri.
PTA was declared an unwanted organism in 2008
and in late 2009 the New Zealand Government announced funding for a long-term management programme. Six government agencies (MAF Biosecurity New Zealand, the Department of Conservation, Auckland Council, Northland Regional Council, Environment Waikato and Bay of Plenty Regional Council) are working together with Maori on a programme that manages the threat of the disease. Landcare Research, together with research partners MAF, Plant & Food Research and Scion, are part of the five-year programme covering research into the detection and spread of kauri dieback and methods to control it.
Mapping where the disease is present and putting containment strategies in place is the essential first step in controlling PTA’s spread. Strategies include taking action to restrict activity around the trees and adopting good plant hygiene practices, such as cleaning boots and tyres and equipment thoroughly before entering and after leaving forests with kauri.
Evidence, based on the symptoms observed and the occurrence of PTA in soil samples, suggests PTA is a soil-borne disease with long-lived resistant spores spread by soil movement, and short-lived swimming spores moved in water flow in soil, as well as spreading tree to tree through close contact of the roots. Soil containing the long-lived spores is likely to be transported around on human footwear and by animals such as pigs. This further emphasises the importance of good hygiene practices where at all possible to ensure soil is not transferred from one site to another, inadvertently bringing the disease along with it.
Research has shown that the disease needs a susceptible host, suitable environmental conditions and a disturbance or introduction pathway which brings the pathogen into contact with kauri roots. It is known that the kauri’s root system, which extends out towards the edge of the tree’s canopy or drip-line, is an extremely sensitive environment; disturbing it places the tree under stress and wounds can provide opportunity for infection. While trees can be placed under stress by events that are out of our control, such as flooding or drought, we can help keep kauri in optimum condition by minimising activities that damage and stress the root system.
Control methods for the disease are being researched. Phosphorous acid (= phosphonic acid or phosphite), which is used successfully to manage Phytophthora diseases in avocado, citrus and other crop trees, is one agent being tested for its potential to control PTA. Preliminary results in glasshouse trials carried out by Dr Ian Horner at Plant & Food Research were very encouraging, showing that phosphite provided good control when applied to kauri seedlings inoculated with PTA. Field trials on forest trees are about to commence.
This article was first published by QEII National Trust in its Open Space magazine, issue 82, March 2012.
FACT FILE ON PTA - kauri dieback
This information and more can be found at www.kauridieback.co.nz
What is PTA?
PTA refers to the deadly kauri disease caused by Phytophthora taxon Agathis. This fungus-like disease was formally identified in 2008 as a distinct and previously undescribed species of Phytophthora.
Scientists are currently working to find control tools for this disease. There is no known treatment at this time.
What does it do to kauri trees?
Microscopic spores in the soil infect kauri roots and damage the tissues that carry nutrients within the tree. Symptoms include yellowing of foliage, loss of leaves, canopy thinning and dead branches. Affected trees can also develop lesions that bleed resin, extending to the major roots and sometimes girdling the trunk as a “collar rot”. PTA can kill trees and seedlings of all ages.
Where did it come from?
Its origin is uncertain but it is believed to have been introduced from overseas.
Where is it?
It has been found in the Waitakere Ranges Regional Park, on private land throughout the Auckland region, in the forest plantations of Omahuta, Glenbervie and Russell in Northland, Department of Conservation reserves at Okura, Albany, Pakiri, Great Barrier, Trounson Kauri Park and Waipoua Forest in Northland, home of our most iconic kauri - Tane Mahuta.
At this stage, the disease has not been detected in many areas of Northland forest, the Hunua Ranges, Hauraki Gulf Islands (excluding Great Barrier) and bush in the Coromandel peninsula. It's imperative that we protect these uninfected areas.
How is it spread?
The spores of kauri dieback (PTA) are found in the soil around affected kauri. Any movement of infected soil can spread the disease. Human activity involving soil movement (on footwear, machinery or equipment) is thought to be the greatest cause of spread. Kauri dieback may also spread though ground water and soil on animals.
What is being done?
The current programme of work includes:
- Research that improves knowledge of how to detect kauri dieback (sampling and DNA-based diagnostic techniques)
- Research that shows how the disease is spread i.e. what are in the infective propagules (fungal outgrowths) in the soil
- Development of an effective treatment method
- Surveillance that determines whether the disease is present, and mapping to show spread
- Assessing the risk posed by the organism to individual trees and their ecosystem
- Public education, cleaning tools provided at high risk sites
- Ensuring a co-ordinated approach to PTA including all communications.
What can we do to stop it spreading?
- Make sure shoes, tyres and equipment are clean of dirt before and after visiting kauri forests.
- Clean shoes and any other equipment that comes into contact with soil after every visit, especially if moving between bush areas
- Keep to defined park tracks at all times. Any movement of soil around the roots of a tree has the potential to spread the disease
- Keep your dog on a leash at all times. Dogs can inadvertently spread the disease if they disturb the soil around the trees
- No dumping of garden green-waste into natural bushland.
What should I do if I have kauri on my land?
- Keep movement, including dogs and stock, away from kauri trees out as far as the drip line
- Download a specially designed warning sign available at this website http://www.kauridieback.co.nz/and put it up to alert visitors to the dangers of spreading the disease. This can be laminated to make it more durable.
- If you think your trees have PTA symptoms contact the Kauri Dieback Management Team on 0800 NZ KAURI (69 52874).
- Go to http://www.kauridieback.co.nz/ for information and resources on PTA.
STOP THE SPREAD - CLEAN YOUR GEAR
Kauri PTA spores will die if there is no soil or water for them to live in. Scrub shoes/boots with soapy water (or a mild bleach solution) to remove all traces of soil and then leave to dry. Once dry you can spray with Trigene disinfectant as an additional precaution. Use Trigene before and after entering kauri areas to treat any soil traces that may still be on your footwear even after cleaning.
Landowners with kauri on their property: contact the Kauri Dieback Team on 0800 69 52874 about getting Trigene.
QEII National Trust covenantors
Your National Trust field representative knows know what to do about safeguarding kauri against PTA. Discuss with them any concerns you have regarding the disease.
This fact file was first published by QEII National Trust in its Open Space magazine, issue 82, March 2012.