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, and
newspaper advertisements.
Weed control progress to date
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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
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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 are you spraying in the wetland?
To kill off 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 are also destroying the habitat for native
water-birds.
Where will you be spraying?
We propose to spray in the Mokoroa Arm is private property in the north western
part of Te Henga wetland. It is at the back of three farms in the valley and is
inaccessible to boat and vehicles.
Will you spray over my house?
No, we will not be spraying over any houses. The closest house is more than 600m
away.
Won't the spray drift over my house though?
No. A combination of spraying on windless days, and using advanced spray
equipment directed onto the trees from a helicopter only a few metres above
them, has been specified to ensure that the spray does not drift outside the
spray area. Before we spray we will have tested the system thoroughly to be sure
that it performs in the way described.
What chemicals are you using?
Glyphosate Green " a Glyphosate; the mildest herbicide available for
spraying over water. Neither this - nor the Pulse “surfactant” - are toxic to
aquatic life or invertebrates. A surfactant is a liquid into which the
Glyphosate is mixed and helps the mixture stick to leaves.
When is the spraying going to occur?
November is the appropriate month but we have not yet decided which year -
indeed the final decision to spray at all, has not been taken " which means it
is a year away at the earliest.
The decision will be made once we have resource consents and have completed
tests which assure residents that the system will perform as we have said, in
that area.
Will you notify us when the spraying is going to happen?
Yes, we are required to do this by law. We will put mailers out to local
residents, notices in the paper and also keep up to date information on our
website.
Does the community get any say in the spraying?
We have undertaken extensive community consultation and have received many
submissions from residents and the wider community both in support and in
opposition to the proposal. All of these comments were considered when the
decision to continue was made.
Has Waitakere City Council made this decision on its own?
No, this is a joint project between Rodney District Council, the Auckland
Regional Council, and the Department of Conservation. This work is a part of the
Waitakere River Flood Protection Scheme that has been running for more than ten
years.
How can I get more information about the spraying?
You can contact us.
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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