Te Henga Wetland Weed Control
As part of the weed control work that has been underway for 10 years in the
Te Henga Wetland Waitakere City Council has proposed to use a helicopter to
spray an area of dense crack willow in an area of the wetland called the Mokoroa
Arm.
Purpose of the Work
For over ten years work has been undertaken to control and eradicate
environmental weeds, especially willow from the Waitakere River and Te Henga
Wetland.
The purpose of this work is long term flood control.
If left unchecked, willows will take over the wetland, clogging the waterways
and potentially exacerbating flooding This reduces the quality of the habitat
for birds and fish and threatens the natural vegetation of the wetland
threatening, in turn, the very high ecological and scenic values of both the
wetland and the Waitakere River.
Methodology and reasoning
As all woody parts of Crack Willows (branch and trunk fragments, etc) can
sprout when in contact with the ground, they should never be felled while still
alive. Rather they should be killed with herbicides and then left standing to
allow native vegetation to grow underneath them. The dead willows break down and
become humus over time.
Limitations to the current work programme
In most of the affected area we have been using the drill and inject and
direct foliar spraying methods to achieve excellent results However, both
requires good access to each tree trunk. With drill and inject for example holes
need to be drilled all around the trunk. Direct foliar spraying is used on
younger trees with stems too small to drill and inject.
These processes have been successful except in the inaccessible Mokoroa Arm
where they cannot be used for practical and safety reasons. This 153 hectare arm
on the north-western side of the wetland has 18 hectares of dense crack willow.
This is the limited area that we propose to spray by helicopter provided we can
demonstrate that the spraying will pose no threat to any other part of the
wetland or the surrounding area.
Glyphosate Green will be used for this operation. It is approved and
recommended for use over water and is the same herbicide currently used in the
wetland (without adverse effects) for the foliar spraying programme.
It is already widely used throughout New Zealand by environmental agencies "
such as the Department of Conservation and the Auckland Regional Council - for
precisely this kind of situation. The Auckland Regional Council has recently
sprayed pampas on the coastal cliffs of the west coast. The Department of
Conservation used helicopters to spray weeds in several wetlands in the Waikato
and Hawkes Bay, with no unforeseen adverse effects. The proposed work in the
Mokoroa Arm is comparable with these instances.
The helicopter pilots are experienced in the application of the spray directly
onto the trees, without wind drift elsewhere, by hanging the machine only a few
metres above the targeted vegetation.
Target spraying is not being considered in unsuitable areas, for example where
there is a tall native bush under-story, or any sites near houses
The stem inject and other spray methods will continue to be used in
accessible areas.
Removing environmental weeds allows native plants to re-establish so the natural
character of the wetland is restored.
Consultation with landowners and the
community
For the helicopter spray option to be considered the agreement of landowners
is the essential first step. The Mokoroa Arm is completely on private property
and all of these landowners have given their full support to the project.
Public consultation occurred in October 2006 and an open day was held for the
community. The community members that responded have been very helpful in
providing feedback, both on the proposed spraying and the weed control work that
has been done to date.
If Waitakere City Council decides that the adverse environmental effects of the
spraying will be avoided or mitigated sufficiently to protect the health and
safety of residents, then spray dates will be decided. Once this occurs,
Waitakere City Council is required by law to notify when the proposed spray
dates will be. This will occur through direct mail drops to local residents.
Weed control progress 2010
In February 2009 a trial was undertaken to control crack willows using a
helicopter. This trial was undertaken at 7am, on a fine still morning in a
remote area of the wetland. The work was carried out by Helisika Helicopters,
and involved six minutes of flying time to control 1.5 hectares of willows.
Waitakere City Council monitored the willows and native plants within the trial
area before the control work, at one month afterwards, three months afterwards
and eight months afterwards. A report has been completed based on the monitoring
which is available from Waitakere City Council or on this website.
The trial was a great success, with willows showing signs of die back within one
month, and with good results from the native understorey. Many cabbage trees
that were poking through the canopy survived the work, and the flaxes are
looking very healthy. There was no spray drift, and very little spray dripped
through the tops of the trees to fall into the water.
With the great success of the trial we will expand the treatment area for this
summer, to the remainder of the Mokoroa Arm. This will require landowner
approvals and a consent with the Rodney District Council which have been
obtained.
It is planned to control another 23 hectares of willows in the Mokoroa Arm of
the wetland (please see map below) with a helicopter. This will enable
approximately 50,000 trees to be controlled in the space of a few hours.
The exact timing and agreement to proceed with this work will be a decision for
the Auckland Council and no further helicopter work in Te Henga wetland will be
undertaken until at least 2011.
Weed control progress 2009
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Helicopter applying herbicide over willows in Te Henga wetland |
The Auckland Regional Council, Rodney District Council, the Department of
Conservation, local landowners and Waitakere City Council recently undertook a
trial of target spraying willows in Te Henga Wetland.
The work was carried out in February 2009 over a small 1.5ha area at the top of
the Mokoroa Arm. A helicopter was used to apply Glyphosate herbicide to the
willows and stringent monitoring has been undertaken over three months to see
what effects there have been.
The trial appears to have been a resounding success so far, with no spray drift,
little damage to native plants but with the willows looking decidedly sickly.
The helicopter company has over 30 years experience with the Department of
Conservation controlling willows in wetlands using helicopters and its expertise
has been invaluable.
The pilot was careful about flying near the edges of the wetland so as not to
damage neighbouring native trees keeping the spray within the centre of the
trial area.
Because of this careful method, willows on the outside edge of the area will
need to be drilled and injected by hand to ensure they die.
The consent for the work requires that vegetation monitoring continues for one
year.
The partnership may look to extend the trial to cover a greater part of the
Mokoroa Arm but will need permission from landowners and to go through a full
consent process.
A full report on the trial and the monitoring results is available. For more
information please contact
council's 24-hour call centre.
Download further information:
Note: You will need to have 
Adobe Acrobat Reader
installed on your computer in order to view and print these documents. For
help opening PDF files or tips on copying information see Helpful
Tips.
Trial Willow Control Monitoring Report (Size
2915K) - A summary of the results of a trial to control willows using a helicopter in the Mokoroa Arm of Te Henga wetland
Te Henga Wetland September Update (Size
1131K) - The latest community update for Te Henga wetland projects
Te Henga Wetland Map with Trial Area (Size
736K) - A map of the general Te Henga wetland area showing the trial willow
control area
Willow Control Best Practice Methods (Size
209K) - Best practice advice for control of willows, demonstrating the range
of methods used by contractors in the wetland
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| Mokoroa arm - Willows prior to control |
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| Mokoroa arm - Willows after one month |
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| Mokoroa arm - Willows after 3 months |
Frequently asked questions
Why will there be spraying in the Te Henga wetland?
To kill crack willows in the Mokoroa Arm of Te Henga wetland.
These willows are environmentally invasive weeds that block the flow of water
and increase the flood risk.
They also destroy the habitat of native birds
Where will the spraying take place?
We will be spraying 23 hectares of willows in the Mokoroa Arm, the north-western
part of Te Henga wetland.
When will the spraying occur?
Weather permitting; the operation will take place one morning in February, 2010.
It is expected to take approximately three hours.
Will we be notified of when the spraying is going to occur?
Yes.
We will put mailers out to local residents, notices on the local notice boards
and also keep up to date information on our website.
Will there be spraying over my house?
No, it is highly targeted spraying.
There will be no spraying over houses, nor will the helicopter fly over any
houses.
How will the spraying operation work?
By spraying on windless days and using advanced spray equipment which sprays
directly onto the trees' canopies from a helicopter only a few metres above them
it ensures no spray drifts outside the intended area.
This method will allow approximately 50,000 willows to be sprayed in
approximately three hours.
Previous trials have been a great success with the willows showing signs of
death within a month and the native plants below the willows' canopies
flourishing.
What chemicals will be used?
Glyphosate Green 510 - a Glyphosate; the mildest herbicide available for
spraying over water.
It is non-toxic to aquatic life or invertebrates.
What organisations have been involved in this decision?
This is a joint project between the Department of Conservation, Rodney District
Council, Auckland Regional Council, and Waitakere City Council.
How can I get more information about the spraying?
Visit our website www.waitakere.govt.nz, or phone our Call Centre on 839 0400. Note: You will need to have
Adobe Acrobat Reader
installed on your computer in order to view and print this document. For
help opening PDF files or tips on copying information see Helpful
Tips.
FAQ Information Sheet (Size
15K)
Make comments and ask questions
You are welcome to contact
staff or send comments on the proposed spraying.
Parks Ecology and Policy Co-ordinator
Waitakere City Council
Private Bag 93109
Henderson
Waitakere 0650
or by email to
info@waitakere.govt.nz.
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