What is kauri dieback?
Phytophthora agathidicida, the pathogen that causes kauri dieback, was only discovered in 2009, and formally named in 2015 (previously it was known as Phytophthora taxon Agathis). The pathogen can sense a kauri tree’s roots, and swim towards them using a tail-like flagella.
There is no cure for kauri dieback, and the disease kills most if not all the kauri it infects. It can be spread by just a pinhead of soil, and you can't tell by looking whether a tree is infected or not. Kauri dieback is threatening kauri with functional extinction. But kauri will be saved – by people like you.
Kauri dieback infects new trees in seven steps:
1: Oospores (resting spores) are introduced into an area of kauri, typically by human activity, but also by animals such as pigs. It only takes a pinhead of soil to move enough oospores to spread the disease.
2. The oospores germinate to form sporangia (a structure which produces zoospores).
3. Zoospores are released during and immediately after rain.
4. The zoospores swim (propelled by their tails) through moisture in the soil towards a kauri’s roots, where they attach themselves to the outside. They then germinate to produce mycelia, a bacterial colony, which infects the root. The tree’s fate is now sealed.
5. The bacterial colony spreads through the root system to attack the tissues at the base of the kauri’s trunk (eventually stopping the transport of nutrients and water to the canopy).
6. More sporangia are formed from where there are areas of infected root. These sporangia release more zoospores during and after rain, ensuring that it is only a matter of time before any other kauri in the vicinity are infected.
7. More oospores form within the tree's infected tissue. These are released into the soil as that tissue decays.
In its inactive state the pathogen can live for many years without a kauri anywhere nearby. It can also survive for many years above ground. So it’s vital that footwear and other gear is cleaned and disinfected before going near kauri, and again before leaving an area with kauri, regardless of how long it has been in storage. Kauri dieback kills kauri of all sizes and of any age – from seedlings to giants that pre-date human settlement.
There is no cure for kauri dieback, and no evidence that kauri have any natural resistance to the disease.