Myrtle rust could be here to stay ministry warns

Myrtle rust is a fungal disease that is found on plants such as pohutukawa and manuka and could be in New Zealand to stay.
Miri Schroeter

Myrtle rust is a fungal disease that is found on plants such as pohutukawa and manuka and could be in New Zealand to stay.

Taranaki could see an explosion in myrtle rust as the temperature warms up, the Ministry for Primary Industries has warned.

Winter weather has so far kept the disease - which attacks myrtle species, including pohutukawa, manuka, and rata - in check, and the ministry is looking at various scenarios to see how it would manage an extensive outbreak.

But it said it's still too early to accurately assess what a widespread infection would mean for the region.

Myrtle rust controlled area in Taranaki.
SUPPLIED/MPI

Myrtle rust controlled area in Taranaki.

"We do not yet have a full idea of how extensive the outbreak could be," MPI incident controller, myrtle rust response David Yard said.

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There's been large scale restrictions put in place for moving myrtle species plants in and out of north Taranaki after the disease was discovered in May.

Manukorihi golf club was temporarily closed due to positive tests for myrtle rust in June.
SIMON O'CONNOR/Fairfax NZ

Manukorihi golf club was temporarily closed due to positive tests for myrtle rust in June.

There are now 78 confirmed sites in the region, mostly around Waitara, and Taranaki is the country's key infection area.

MPI would get a better idea of how far reaching the problem was in the coming months, Yard said.

"Being realistic, we do anticipate that myrtle rust will be quite widespread, given our belief that the disease arrived here from Australia in one or more significant wind events.

Brent Rogan of the Ministry for Primary Industries checks trees in Taranaki for myrtle rust.
SIMON O'CONNOR/Fairfax NZ

Brent Rogan of the Ministry for Primary Industries checks trees in Taranaki for myrtle rust.

"Spores may have been deposited across large areas of the North Island and possibly even the upper South Island."

Yard said along with the Department of Conservation MPI had been carrying out surveillance across the area which resulted in the discovery of four new confirmed infected properties in Otorohanga on September 8.

MPI was developing its options for future management of the disease based on various scenarios, he said.

"It may be that full eradication from New Zealand is not feasible and this could result in a longer term management programme which may attempt to slow the spread of the disease, manage biodiversity and heritage/taonga trees at important sites, and invest in the science and tool development necessary to allow future management of the disease."

Yard said it was too soon to accurately evaluate what an extensive infection would mean for Taranaki.

"We still have to wait and see what the impacts on biodiversity, culture, heritage and economic values would be, as it is just too early to tell how the disease will affect native and exotic species in the region."

Myrtle rust forced the closure of Waitara's Manukorihi Golf Course in May, where a number of trees were cut down, and other courses have been on alert for signs of infection.

Yard said MPI continued to run activities in Taranaki from a field headquarters and was still investigating new reports of suspected infections.

"Activities include surveillance of all host plants [myrtle species] in the area within a 50 metre radius extending out from each confirmed infected site. We are removing any affected trees and plants that are found.

"Our focus right now is building an accurate picture of where myrtle rust is present in New Zealand to enable us to make the best decision on how the disease is managed in future."

Movement restrictions on myrtle species remain in place, however feijoa plants were removed from the list last week.

"Based on evidence collected as a result of the biosecurity response and advice from international experts, MPI has concluded that feijoa does not appear to be susceptible to myrtle rust or carry any significant risk of transmitting the disease to uninfected myrtle plants," Yard said.

The restricted zone stretches from Omata in the west, to Uruti in the north and south to lake Ratapiko and it's illegal to move any plants or trees belonging to the myrtle family and any garden waste or prunings from those plants out of the area.

 - Stuff

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