A microscopic water mould called Phytophthora agathidicida. It is new to science and lives in the soil and has two forms. The soil form is in tough spores called oospores that can survive in dried soil on boots and equipment for up to 8 years (and counting). It also has a water borne spore with a tail that can swim called a zoospore. However this is short lived and is killed by seawater, but can move through the water film in the soil up to 3m per year.

Almost exclusively by soil disturbance. The greater amount of disturbance the greater risk of spread. Large animals like humans & pigs move kilos of soil around the forest on feet and equipment (and in pig guts) and are the primary vectors. Small animals like birds, rats, possums etc move only miniscule amounts of soil and are a negligible risk. Dogs are a moderate risk and should be on leads at all times in forest areas. The water borne zoospore can swim downhill in water films in the soil and in watercourses. The “natural” spread of the disease via water is estimated at 3m per year.

By removing the main vector humans from risk areas where there are infected and healthy kauri, in other words keeping people out of kauri forests. This will remove at least 70% of the problem in the Waitakere Ranges. At the same time pigs, the other main vector, need to be eradicated. Fencing off areas of healthy kauri ecosystem to prevent pigs and humans from bringing the disease into them is necessary and a priority.

Upgrading the track infrastructure to make the tracks dry and get them off kauri roots will minimise the risk of moving soil around and spreading the disease. Boardwalks and engineered tracks that are convex and allow water to run off them instead of pooling and creating a mud slurry is what is required urgently. Tracks should be rerouted away from kauri if possible.