page_title: Kauri dieback
section_title: Transmission
hierarchical_section_title: Kauri dieback / Transmission
caption_attribution_description: English: Footwashing station (version 2 design) at Trounson Kauri Park, to stop the spread of Kauri Dieback.
context_page_description: Kauri dieback is a forest dieback disease of the native kauri trees of New Zealand caused by the oomycete pathogen Phytophthora agathidicida. Symptoms include root rot and associated rot in a collar around the base of the tree, bleeding resin, yellowing and chlorosis of the leaves followed by extensive defoliation, and finally, death.
context_section_description: The disease is solely soil-borne and mostly spread in infected soil carried from tree to tree. P. agathidicida spores can be carried in soil the size of a pinhead. The consensus among experts is that the predominant vector for spread of the disease is human activity.  This can be seen as 71% of the infected trees in the Waitākere Ranges are within 50 metres of public walking tracks.
  Phytophthora zoospores require water to germinate from the oospore, and can migrate by themselves through waterlogged soil. P. cinnamomi zoospores remain mobile for up to 10 hours, and can swim at speeds of up to 58 centimetres per hour. However, their direction of travel frequently changes, so they disperse no more than 6 cm by swimming. Consequently, long-distance dispersal of Phytophthora depends on other forms of transport.
  Feral pigs have been blamed for the spread of kauri dieback due to their tendency to gnaw on the roots of kauri trees, and to transport infected soil on their snouts and trotters. Research in 2017 suggests the transport of infected roots via the gut of pigs is a relatively minor vector for the spread of the disease.
  While only kauri trees develop the characteristic dieback disease following infection, it appears that seven other native New Zealand forest plants can act as hosts for the pathogen without showing symptoms themselves. These include Dracophyllum, tanekaha (Phyllocladus trichomanoides), tall mingimingi (Leucopogon fasciculatus), rewarewa (Knightia excelsa) and Astelia trinervia. It is thought that the community of symbiotic mycorrhizal fungi living on the roots of healthy kauri trees may help protect them from Phytophthora infection.
caption: Footwashing station at Trounson Kauri Park, to stop the spread of kauri dieback
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