Long and unkempt grasslands around Napier are helping protect the Bay from a pest, not a sign the council is behind on its mowing.
Napier City Council's "No mow" signs are part of a Hawke's Bay Regional Council and MAF programme to eradicates phragmites.
The giant grass invades wetlands and water margins,
crowding out native plants and destroying native birds' habitats.
Council plant pests biosecurity team leader Darin Underhill said the plants phragmites' roots were strong enough to penetrate concrete and could block drains.
"It's only found in two places, around Napier and around Christchurch, and Biosecurity New Zealand is trying to eradicate it from New Zealand," he said.
"It is reducing each year, we will win eventually."
The plants would be left to grow 600 to 800mm and would be hand sprayed with Unimaz herbicide, which had been used successfully over the last decade to control phragmites.
Spraying when the plants had been mowed was not as effective because smaller plants meant less chemical was taken in.
Once the plants were taller they would absorb more of the herbicide.
The plants probably spread and became established after root fragments were spread by mowing or other machinery.
Mr Underhill said the council and MAF would control phragmites plants found in private gardens at no cost to landowners.
Anyone who saw plants they thought were phragmites could call the council on 0800 108 838.
