Kauri dieback

The disease is caused by Phytophthora agathidicida, an oomycete pathogen that specifically attacks the root system of trees. This organism functions similarly to fungi but is distinct in its biological structure, acting as a highly invasive soil-borne parasite that disrupts nutrient uptake.

The primary host for this pathogen is the Kauri tree (Agathis australis), an iconic and ancient conifer species. The infection leads to a severe condition known as Kauri dieback, which has become a significant conservation challenge in New Zealand, threatening the survival of native forests.

Key symptoms include yellowing and premature dropping of leaves, canopy thinning, and distinct lesions or bleeding cankers on the lower trunk. These lesions often exude large amounts of resin, reflecting the tree's physiological stress as the root system fails to function correctly.

Environmental conditions conducive to the pathogen's development include high soil moisture and warm temperatures. The organism produces zoospores that swim through water films in the soil, allowing the disease to spread rapidly when soil is muddy and easily transferred by human or animal foot traffic.

Management focuses on rigorous sanitation and biosecurity protocols. Since there is no reliable cure, the main preventive efforts involve cleaning footwear and equipment at sanitization stations, boardwalk construction to minimize soil disturbance, and restricting human access to infected areas.

• Bleeding resinous lesions on the trunk.
• Yellowing and canopy thinning.
• Dead branches in the crown.
• Root decay and necrosis.
• Stunted growth and premature tree mortality.