Myrtle rust is a 'big worry' for Auckland's Waitakere Ranges
If myrtle rust makes its way to the Waitakere Ranges the result could be devastating.
The fungal invader that was expected to arrive on the wind from Australia was found for the first time in New Zealand this May next to and at a garden centre in Kerikeri and then in three places in Taranaki.
Waitakere Ranges Protection Society president John Edgar said it was probably just a matter of time until it infected the native forest on Auckland's west coast that he was a guardian of.
"It's a very big worry. We are very concerned," Edgar said.
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"But it's like kauri dieback – what can you do about it, you know? I mean, you can't go around and spray every tree."
The disease affected trees of the myrtle family, including New Zealand natives such as pohutukawa, rata, manuka and kanuka.
As a regenerating forest, the Waitakere Ranges was full of these, especially manuka being a tree quick to take off and that keeps weeds down allowing taller trees to emerge, Edgar said.
The affect on pohutukawa would also be "very, very, serious".
"Pohutukawa grow on cliffs and their roots are very tenacious and they stabilise those cliffs. So if we lose pohutukawa then we are going to have a lot of erosion on the coast."
Edgar said he hoped the outbreaks would be controlled but he said the disease was expected to establish in the country at some stage.
"Because it's a airborne microscopic fungus, you can't do anything to stop it.
"It's spread by wind, and if you went and picked up an infected leaf and got the spores on your hand and then touch another tree 100 metres away, then you've just spread the disease."
Not all infected trees would die, but they would get knocked back.
Edgar said he felt powerless to do anything about it except to spread the word and hope it can be contained.
The Ministry of Primary Industries' website said it is not known how myrtle rust would affect New Zealand species, and its impact had varied widely from country to country and among species.
"Severe infestations can kill affected plants and have long-term impacts on the regeneration of young plants and seedlings," it said.
"The spores are thought to be capable of crossing the Tasman Sea from Australia to New Zealand on wind currents."
People who spotted the yellow fungus should not touch it, but instead take a photo, note the location, and call the Exotic Pest and Disease Hotline on 0800 80 99 66.