Detection, surveillance and diagnosis
Risk pathways and vector research
Knowing how the disease spreads, underpins what tactics and tools are required to find where the disease is located.
The disease is soil-borne hence it can spread vast distances by movement of contaminated soil. It also spreads naturally through soil water. We estimate that the natural spread of the pathogen is around 3 metres per year. It can also spread by root to root contact as a lot of kauri grown in kauri stands have their roots interconnected as well as by movement of infected kauri wood. There is no evidence to suggest the disease can be transmitted in kauri seeds or cones unless they are contaminated with soil.
Although we have not detected the pathogen in water bodies such as streams or creeks, it is possible the pathogen can disperse downstream especially in times of flooding.
Laboratory research has found that pigs can also act as vectors to the disease although the level of risk is uncertain at this stage.
As far as we are aware, only kauri has been found to be infected with the disease although laboratory research suggest that other native plant species may be susceptible to the disease as well. Extensive field trials are currently being done to validate these research findings and to determine if other plant species can host or carry the disease.
By far the greatest amount of movement of the disease is attributed to human activities. A number of observational studies imply that the movement of contaminated soil on people and associated vehicles & equipment, represent the greatest risk of spread. Given the high frequency of visitors to the forest and the type of activities being carried out, increases the likelihood of large amounts of contaminated soil being removed inadvertently from within and between kauri forests.
Aerial Surveillance and Ground Truthing
A large component of our operations involve aerial surveillance and ground truthing (via soil sampling). Finding where the disease is, involves locating trees with dieback-like symptoms using aerial surveillance, and confirming whether these symptomatic trees are infected with the pathogen through ground-truthing.
Early research focused on developing tools that enables us to accurately diagnose the pathogen from the soil as well as an understanding of the spatial distribution of the pathogen in and around kauri. This has allowed us to optimise laboratory methods and sampling tactics to increase the likelihood of detecting the pathogen as well as guidelines to manage the risks associated with certain activities in the forest.
We know that the disease has a patchy distribution, across most regions where kauri are found but we are less certain in knowing if a forest or an area of the forest or even an individual tree is completely disease-free. It is impractical to sample and test all soil around kauri due to the time and cost involved. And given there is a lag time (or delay) between when a tree becomes infected to when disease symptoms appear makes it even more difficult to ascertain whether a tree is infected or not. Consequently, we are taking a precautionary approach in disease control and management, in treating all kauri as potentially infected.
Ongoing research aims to test and refine existing diagnostic & surveillance tools and to explore potentially innovative new ones, which are more cost effective and allow us to diagnose the pathogen and find the disease more rapidly. In addition we are exploring other ways in how we define an area free of the disease. The use of epidemiology, remote sensing and Cultural Health Indicators are some examples currently being explored.
If you have any questions in relation to this area of research or the supporting reports please contact the Kauri Dieback team on the details below.
Please note that as more information becomes available on the nature of kauri dieback disease and the pathogen that causes it, some of these papers may be superseded.