Kauri Killer on the Loose
by Jo Ritchie

We have victims and a chief suspect but the modus operandi of Phytophora taxon agathis is still much of a mystery.
 

 

One of Northland’s iconic forest giants is under mortal attack from a fungus-like microbe fungus known as Phytophthora taxon Agathis. It’s hard enough to spell let alone remember—hence the abbreviation to PTA.

Phytophthora is Greek for plant killer and Agathis is part of kauri’s Latin name (Agathis australis. Unlike traditional forest pests like rats and possums which you can see, PTA is invisible and often only detected when trees are in an advanced state of decline.

Folige dieback. Photo courtesy of ARCSparse crowns - photo courtesy ARC


A number of trees have already died and to date we have no known cure. The biggest problem is that very little is known about PTA and this makes it very hard to come up with a solution. However there is a lot we as regular users of kauri forest can do to help those trying to manage it as well as to prevent its spread so read on.

What is PTA?
PTA is a microscopic fungus-like plant pathogen (a disease causing agent) that is believed to be soil borne. It is specific to kauri and can kill trees and seedlings of all ages. Recent research has identified PTA as a distinct and previously undescribed species of Phytophthora.

What does it do to Kauri? Bleeding resin - photo: IslandStay
PTA infects kauri roots. 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. This is known as ‘collar rot’. The resin flow has also been identified in the crown; this makes it more of a problem as the spores that spread the fungus can now be dispersed via air as well as soil and water.

Where did it come from?
Great Barrier has a dubious claim to fame as it was first recognised on the island in the early 1970’s by Dr Peter Gadgill but unfortunately it was not formally identified in April 2008. PTA’s closest known relative is a chestnut pathogen from Korea (P. katsurae). The assumption is that it is an exotic pathogen. The scary part is that nothing is known about this particular species overseas.

How is it spread?
PTA is believed to be a soil borne species spread by air, soil and water movement, plant to plant transmission through underground root-to-root contact (hence the reason stands of trees get infected at the same time), and human and animal vectors.

Feet are a key source… Feral animals, e.g. pigs, dogs and in soil on shoes or tyres.

Where is it?
In order to define the extent of PTA, regional councils and D.o.C are conducting delimiting surveys. To date it is been found in Northland, Auckland and Great Barrier. Sites include a number in the Waitakere Ranges, on the Awhitu Peninsula and in Trounson Kauri Park and Waipoua, forests. These surveys extend over private as well as publicly owned land.

Who is managing it?
This disease is considered a really big deal. In October it was declared an ‘unwanted organism’ under the Biosecurity Act 1993. This formalises the status of PTA as a serious threat to our natural environment. An interagency response team has been formed and includes representatives from MAF Biosecurity NZ, D.o.C and the 4 regional councils in the area where Kauri is naturally found – ARC, Northland Regional Council, Environment Bay of Plenty and Environment Waikato.

What are they doing?
Delimiting surveys to identify how widespread PTA is. A technical advisory group is working to find answers to key questions including how to detect it, how to limit its spread and whether it can be controlled and if so by what. Field officers are responding to calls from concerned people and undertaking visits. A public awareness programme is also being implemented.

How you can help?
At this stage access to public reserves where kauri is present is not being restricted in any way. To allow this to continue there are some simple preventative measures you can take to prevent spreading the disease.

Be better informed by accessing the website: www.kauridieback.co.nz or call 0800 NZ Kauri (0800 69 52874). The website contains excellent information including how you can prevent spread. You can also report diseased trees to the 0800 number.

When you visit Kauri forests
• Read and abide by warning signs
• Walk over the mats at track entrances if they are in place. These contain a fungicide and work on the same principle as used in foot and mouth epidemics
• Stick to defined tracks in parks and reserves
• Clean footwear, tyres, any equipment in contact with soil before & after leaving kauri forest
• Minimise movement & disturbance around kauri tree roots
• Keep dogs and animals away from trees
• If you are pig hunting — do it legally with a permit and check with who you get a permit from whether they want any specific information and/or whether there are any specific precautions you can take.

What should I do if I have Kauri on my land?
Implement the same procedures as above for visiting kauri forests.

• Download a warning sign from the website and put it up to alert visitors to the dangers of spreading the disease. Laminate the sign to make it last longer
• If you think your trees have PTA symptoms call 0800 NZ Kauri
Preventing the spread of PTA and the loss of an iconic species and all the native species that rely on it requires everyone’s help. It’s not hard to play a part so get in behind it.
Thanks to Nick Waipara, ARC, (www.kauridieback.co.nz) and Martin Herbert, Treescape Ltd for assistance with writing.