Kauri dieback is caused by a Phytophthora fungus that infects and kills kauri throughout its distribution in the north. It spreads through soil contamination, including on footwear, clothing, vehicles and animals. There is no known cure and it is essential to control the spread of the disease.
Symptoms include root rot and associated rot in a collar around the base of the tree, bleeding resin, yellowing of the leaves, extensive defoliation, and death.
Nurseries play an important role. Phytophthora agathidicida can rapidly spread through young kauri. Contaminated plants shipped from nurseries to kauri forests, restoration areas, amenity plantings and home gardens is a risk which can be managed by plant producers.
Key opportunities for Phytophthora to enter a nursery and spread through its production cycle include:
- Contaminated propagules or imported infected (but possibly asymptomatic) plant materials and any associated soil
- Contaminated water, potting and growing media or pots
- Poor sanitation and contaminated equipment