It is not native. It arrived on the wind in 2017, likely from Australia, and has since become a permanent resident. Austropuccinia psidii is a fungus that targets the Myrtaceae family, which includes some of New Zealand's most iconic plants. Pōhutukawa, rātā, mānuka, and kānuka are all vulnerable. The infection manifests as bright yellow, powdery pustules on young leaves, shoots, and flowers. These spores are prolific. They ride air currents, settling on any susceptible host within range. The damage is structural. Infected leaves curl and die. Shoots deform. Heavy infections can kill young plants outright and weaken mature trees, making them susceptible to secondary pests. The visual impact is stark. A pōhutukawa that should be vibrant with red summer blooms may instead appear scorched and stunted. This changes the aesthetic of the coastline. It changes the ecology. Many native insects rely on myrtle nectar and pollen. When flowering is reduced, those insects go hungry. The spread is relentless. Unlike soil-borne pathogens, this one does not require physical contact. It travels on the breeze, making containment nearly impossible. Nurseries and growers face strict biosecurity measures, but wild populations are largely exposed. Climate change may exacerbate the issue, as warmer temperatures favour fungal growth. The response has been a mix of surveillance, breeding for resistance, and public awareness. People are asked to report sightings. Scientists are screening for resistant genotypes. The outcome remains uncertain. The rust is here. It will not leave. The question is how much of the myrtle family will survive it.