Aerial spraying could resume to eliminate willows

A proposal is on the table to bring back aerial spraying this summer to wipe out pest plants in a section of Waitakere bush.

But Waitakere City Council is playing down the proposal's apparent parallels to the controversial spraying campaign to eradicate painted apple moth.

The target this time is not insects, but invasive crack willow and grey willow trees that have a grip in parts of Te Henga wetland.

Waitakere City and Rodney District Councils have tried since 1994 to get the pest plants under control with partial success. Now the Waitakere council is keen to launch an aerial spray of the hard-to-reach areas, using a herbicide already in use by other government departments.

The purpose of willow control is mainly to lower the risk of flooding, as the trees commonly block peoples' drains. They also take over areas of native vegetation.

The council's public affairs manager Dai Bindoff says this project and the last one are "like chalk and cheese".

"The painted apple moth spraying was carried out over the entire urban and parts of the rural part of the city, repeatedly, for two years. Mostly, this was applied in 'broad brush fashion' with a fixed-wing aircraft. The willow spray will be delivered at low level, by helicopter.

"It is entirely in a rural area and low, targeted spraying in ideal wind conditions will ensure no impact on humans."

The herbicide is Round Up G2 , designed for use around water. The Auckland Regional Council and Department of Conservation are both known to use it.

Forest and Bird Society planner Mark Bellingham, who has worked on willow eradication projects since 1995 and also lives next to the wetland, says the herbicide will have no effect on most people.

The area in question is used recreationally in the summer, especially by kayakers, but there are few residents. He expects they will have the option of going on holiday when the spraying is underway, and have their roofs washed down afterwards: "If people want an alternative source of water for a while then that is provided."

Willows can regenerate from living twigs or bark that break off and take root.

So far the "drill and inject" method the conservation team has used - get poison into the stem and wait for it to die - has taken too long. A tree is still able to produce new trees in the time it takes to die.

Manual control of the plant, at a cost of $300,000, is seen as "problematic and expensive", according to a report to the city development committee by parks ecology and policy co-ordinator Jacki Byrd.

- THE AUCKLANDER