What is kauri dieback disease?
- Kauri dieback disease is caused by a microscopic spore which lives in the soil.
- These tiny spores are fatal to our iconic kauri trees.
- The spores cause root rot and the trunk of the kauri to bleed sap, lose leaves and eventually die.
- Kauri dieback disease infects trees in seven steps:
- Oospores (resting spores) are introduced into an area of kauri, typically by human activity, and probably by animals such as dogs, possums, and rats. It only takes a pinhead of soil to move enough oospores to spread the disease.
- The oospores germinate to form sporangia (a mass of threads which produces zoospores - live swimming spores).
- Zoospores are released during and immediately after rain.
- 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 (branded tubular structure) which infects the root. The tree’s fate is now sealed.
- The mycelia spread 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.
- 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.
- More oospores form within the tree’s infected tissue. These are released into the soil as that tissue decays.
How is it spread?
- By water running across or through soil.
- In soil on people’s or animals’ feet or on tools and equipment.
How long does it take to appear?
It may take some time for the symptoms to appear so care is needed not to walk past kauri trees because you can unknowingly carry spores from a tree that is sick, but doesn’t show it yet, to other trees.
Can it be cured?
We have no known cure for kauri dieback disease and once a tree is infected, it dies. The injection of phosphite can boost a tree’s resistance to the disease, but is not a cure.