Comparison of weed control methodologies for hard edging in local parks and the urban road corridor
Method
Effectiveness
Costs (average)
Environmental Impacts
Human health risks
.
No control
In most situations, no control would result in council’s failure to meet
No immediate direct cost.
In some cases native species may co-exist with weed
Perceived or actual indirect impact from the growth
current level of service.
species if the weed populations do not dominate to the
of weeds:
Where no weed
Unquantified potential longer- term
point of excluding native species suited to the particular
Species like privet can trigger hay fever
control is
No control can be effective in some parts of the rural road corridor for
costs from damage to assets caused
habitat. More commonly weeds do out-compete and
and asthma. 4
undertaken at a
some species. For example, no control of gorse can lead to successful
by weeds (cracks in footpaths, car
therefore eliminate native plant populations3.
Other species can present a physical
particular site.
regeneration of native species1.
parks etc.).
hazard (e.g. moth plant sap is an irritant)5.
In a few other situations where erosion control is more important than
species composition, no control of weeds is an effective option2.
Mechanical
Mechanical control methods are not effective ways of killing the entire
For the road corridor, the costs for are
Some potential impact on biodiversity, via risk of
There is a minor risk of injury to the applicator from
plant including the root system, but they trim foliage and can prevent or
difficult to separate out as mechanical
spreading weeds as fragments can travel on machinery,
equipment, or to passers-by (e.g. from stones being
Weed-eating,
reduce seed production and restrict growth. Mechanical control is used
control is used in conjunction with
or re-sprout from fragments on site.10
flicked up by machinery/line trimmers).
mowing,
most often in combination with other weed control methods in the road
other methods in the different contract
shredding.
corridor (glyphosate, steam and hot water) to increase effectiveness.
areas. The estimated cost for the
The equipment used for mechanical control may use
mechanical only method in the road
some fuel. Fuel consumption and associated carbon
Used on 1,615 km
Mechanical control methods must be undertaken between weekly and
corridor is $2000/km per year8.
emissions have not been quantified.
of hard edges in
monthly, depending on the required level of service, to prevent weeds
local parks6, and
from resprouting from stem and root fragments.
For local parks the average cost is
the road corridor
$1,684/km per year within a range of
in conjunction with
Mechanical control is most effective when it is timed well, e.g. before a
$1,229/km (high use rural park) to
other methods.
plant can set seed7.
$8,553/km (premier park) depending
on location and control frequency9.
Manual
Manual control is not an effective method for most of the hard edges in
Cost for this method is site specific.
This method creates soil disturbance, which can lead to
There is risk to the applicator through injury via
local parks, nor for much of the road corridor. It can be effective against
The need to manually remove weeds
weed invasion15. Manual control on species that re-sprout
over-exertion during operation or injury/illness
Weed control by
small shrubs and trees and herbaceous weeds in small infestations,
makes it generally more expensive
from fragments can lead to weeds spreading further16.
caused by weed itself (e.g. reaction to sap, or injury
hand or hand tool.
removing the whole plant11. It is best suited to small plants without
than alternative less labour intensive
from appendages such as thorns). Personal
extensive root systems that can be removed without breakage. It is not
methods.
Protective Equipment (PPE), such as long sleeves,
recommended for plants with deep underground roots and/or easily
pants and gloves, will minimise risk17.
broken roots.12
Most weeds should be removed from the site entirely to avoid fragments
or seed colonising.13 Careful disposal is important for some species (e.g.
those that resprout from fragments, such as tradescantia)14.
1
High Pressure
Steam is not an effective way of killing the entire plant including the root
$1,561/km per year in the road
This method uses 2000L to 3000L of water per day of
Primarily risk to the operator through direct contact
Steam
system, but it treats the foliage and can prevent/reduce seed production
corridor 23.
deployment24. The environmental impacts of this water
with hot water, equipment and proximity to traffic.
and restrict growth19. The steam destroys the surface foliage of the
consumption will be dictated by whether the water is
Application of high
weeds, leaving the roots primarily untreated as the temperature of the
sourced from the mains supply or from roof supply, and
Exposure to the steam is minimal and the heat
pressure steam.
steam decreases (forming liquid water) rapidly upon touching the
has not been quantified.
dissipates quickly once the steam contacts the
Includes
ground20.
weeds or ground. Risks caused by exhaust have
supplementary
Similarly the environmental costs from heating the water
also potential to cause harm25.
applications of
Steam does not destroy the foliage of some types of weeds (nutgrass
and powering the vehicles used for transporting the
glyphosate or
and kikuyu for example).
heated water to the site, will depend on the sources of the
In the road corridor the treatment operator is
mechanical
energy being consumed. If fossil fuels are used there will
exposed to moving traffic as they walk alongside the
treatment.
Steam must be repeated on a 6 weekly programmed cycle in
be associated carbon emissions. These have not been
truck. This is minimised by treating the kerb and
combination with or interspersed with mechanical trimming/removal to
quantified.
channel from the berm/footpath.
Used in
achieve the required level of service to meet required service standard 21.
approximately
700km (9%) of the
To achieve required level of service in this contract area, mechanical
road corridor in
control (weed eaters) is used to remove any weeds in the channel or
north-east urban
growing over the kerb before high pressure steam is applied to the
contract area of
remainder of the plant. High pressure steam is used every second cycle
legacy North
with the intervening cycle being mechanical only. Weed eaters are also
Shore18.
used to trim the edges of the footpath. Glyphosate-based herbicide is
used to kill the weeds in the channel on the Level 2 roads as the high
pressure steam system (trucks and application system) cannot be used
safely on these roads, with mechanical control (weed eaters) used on the
road berm. Glyphosate is also used to treat specific weeds such as nut
grass.
The current high pressure steam system is too heavy to be accomodated
on park infrastructure such as footpaths and lawns, and is only used in
the road corridor. Application involves large, slow moving vehicles which
are noisy22, so it is limited to non-peak hours in some areas. Traffic
management is required for high volume roads (L2).
Hot water
Hot water treatment is not an effective way of killing the entire plant
$1,186/km per year in the road
This method uses 5000L to 6000L of water per day of
Primarily risk to the operator through direct contact
treatment
including the root system, but it treats the foliage and can prevent/reduce
corridor 30.
deployment32. The environmental impacts of this water
with hot water, equipment and proximity to traffic.
seed production and restrict growth27. The hot water destroys the surface
consumption will be dictated by whether the water is
Application of hot
foliage of the weeds, leaving the roots primarily untreated as the
The current frequency of application
sourced from the mains supply or from roof supply, and
Exposure to the hot water is minimal and the heat
water.
temperature of the water decreases rapidly upon touching the ground.
does not meet the level of service
has not been quantified.
dissipates quickly once it contacts the weeds or
Supplemented
required. To meet the required service
ground. Risks caused by exhaust have also
with mechanical
Hot water does not destroy the foliage of some types of weeds (nutgrass
standard, the treatment frequency
Similarly the environmental costs from heating the water
potential to cause harm34.
removal of larger
and kikuyu for example).
would need to be doubled with an
and powering the vehicles used for transporting the
weeds.
extrapolated costs is approximately
heated water to the site, will depend on the sources of the
In the road corridor, the treatment operator is at risk
In this contract area, hot water is applied directly to the weed with no
$2,372/km per year31.
energy being consumed. If fossil fuels are used there will
to moving traffic as they walk beside the truck on
Used in
mechanical control undertaken prior to application of the hot water. Some
be associated carbon emissions. These have not been
the road.
approximately
mechanical control is used to trim the edges of the footpaths. No
quantified.
735km (9%) of
glyphosate is used in the area where hot water is used.
road corridor in
Thermal treatment can reduce soil micro-organisms and
north-west urban
Control is repeated within an 8 weekly programmed cycle in combination
invertebrates33.
contract area of
with mechanical trimming/removal. This cycle is not frequent enough to
legacy North
achieve the required level of service28.
Shore26.
The current hot water treatment system (trucks and disposal unit) is too
heavy to be accomodated on park infrastructure such as footpaths and
lawns, and can only be used in the road corridor. Application involves
large, slow moving vehicles which are noisy29, so it is limited to non-peak
hours in some areas. Traffic management is required for high volume
roads (L2).
2
Plant-based
Plant-based herbicides are activated on contact with the foliage of weeds
$1,459/km per year in the road
The vehicles used to apply plant-based herbicides use
Exposure pathways for occupational and public
herbicide
and brown off the foliage thus can prevent/reduce seed production and
corridor for Bio-Safe (within a range of
fossil fuels and generate some carbon emissions. There
exposure are managed by compliance with
restrict growth.
$1,363 - $1,577/km per year)44.
is concern that some plant-based herbicides contain
standards and procedures.
Weed control by
ingredients that contribute to other environmental effects
plant-based
They are usually fast acting38, and they can control some weeds that hot
such as coconut oil. Some of these products are acidic
Meets national health standards when correct
herbicide via foliar
water and steam don’t affect (such as kikuyu)39.
and can be corrosive. These have not been quantified.
application methods and procedures are adhered to.
spray.
The EPA has approved Organic Interceptor and
Includes products
Organic Interceptor is a non-selective contact herbicide that causes rapid
Direct application of Organic Interceptor may kill
Agpro Bio-safe as a herbicide for use under the
like Organic
dehydration by penetrating green tissue and disrupting normal
beneficial insects and bacteria45.
Hazardous Substances and New Organisms Act
Interceptor
membrane permeability and cell physiology40.
(HSNO) Act 1996.
(derived from pine
Bio-Safe is inactivated on contact with the soil and has no
essence35) and
Bio-Safe is a non-selective contact herbicide that causes rapid wilting of
residual activity46.
Correct application methods are described in the
Agpro Bio-safe
the leaves and is most effective on actively growing weeds and when
New Zealand Standard on the Management of
(derived from
applied in hot sunny conditions41.
Agrichemicals (NZS 8409:2004), Proposed
coconut oil36).
Auckland Unitary Plan (part 3.H.4.9.2.2 and .3), and
To meet service standards they must also be used in combination with
product label as registered by the EPA. Application
Used in
other methods, and they require more frequent application compared to
must be in accordance with these standards.
approximately
glyphosate42. Biosafe is used on a 4 weekly cycle and is supplemented
1049 km (13%) of
with glyphosate. Interceptor is used on a 12 day cycle in combination
Agpro Bio-safe carries a health and safety risk to
road corridor in
with mechanical removal.
the operators and others who come into contact with
legacy Auckland
the product. The product is corrosive to eye tissue
City and Waiheke
A 2002 trial into weed control methods by the legacy Waitakere City
and an eye, skin and respiratory irritant. Protective
Island area37.
Council found that Bio-safe was reliably effective only when vegetation is
equipment must be worn47.
young especially kikuyu grass. The same trial looked at Organic
Interceptor and glyphosate, and found it the least effective in the trial at
Biosafe is a coconut derived fatty acid with a strong,
controlling established vegetation especially kikuyu.43
notable odour. This odour persists for some time
after treatment, longer on warm days, and has been
the source of complaint from the public.
Glyphosate-
Effective tool for controlling annual broadleaf weeds, grasses and other
In the urban road corridor the average
Approved for use the New Zealand Environmental
Exposure pathways for occupational and public
based herbicide
monocots affecting hard edges in local parks and found in the road
cost is $562/km per year54 (within a
Protection Agency (EPA).
exposure are managed by compliance with
corridor. It kills the entire plant including its root system50. It requires less
range of $300 - $779/km per year)55.
standards and procedures.
Application of
frequent follow ups than other methods, with an average of three to four
Glyphosate is strongly absorbed into soil and has no
approved
treatments a year.
For local parks the average cost is
residual activity in soil57. This reduces the risk of the
Meets national health standards when correct
herbicide through
$413/km per year within a range of
product being transferred due to rain or irrigation, and the
application methods and procedures are adhered to.
roller ball or foliar
Glyphosate is absorbed through green plant tissue then translocates
$383/km (low use park) to $719/km
risk of the product being taken up by non-target plants58.
The EPA has approved glyphosate as a herbicide
spray.
throughout the plant including the root system to kill the entire plant 51.
(high use rural park) per year
It has a low toxicity to terrestrial animals and wildlife59.
for general use under the Hazardous Substances
Effectiveness requires weeds to be actively growing and not under
depending on location and control
and New Organisms Act (HSNO) Act 1996.
Used on 3,621km
drought stress, with clean foliage for best results.52 Effectiveness is also
frequency56.
Over use can result in increased resistance in some
of hard edges in
enhanced when sites are prepared using mechanical weed control
species, and therefore effectiveness could decline over
Correct application methods are described in the
local parks48 and
methods that reduce or prevent seed production.
time60.
New Zealand Standard on the Management of
the in
Agrichemicals (NZS 8409:2004), Proposed
approximately
Nutgrass suffers only a knock-down effect from glyphosate due to the
The vehicles used to apply glyphosate use fossil fuels
Auckland Unitary Plan (part 3.H.4.9.2.2 and .3), and
5500km (69%) of
inability of glyphosate to penetrate the plant’s thick cuticle. However
and generate some carbon emissions. These have not
product label as registered by the EPA. Application
the road
experience shows that when mixed with a wetting agent, glyphosate is
been quantified. Similarly the life cycle impacts arising
must be in accordance with these standards.
corridor49.
effective in killing nutgrass53.
from the manufacture, transport and storage of
glyphosate have not been quantified.
There is some community and international expert
The application rate is quick (using a small left-hand steer vehicle).
debate of health risk. In March 2015 a World Health
Organisation (WHO) sub group, the International
Agency for Research on Cancer (IARC) Working
Group, re-classified glyphosate as ‘probably
carcinogenic to humans (category 2A).61 However,
the EPA has noted that another WHO assessment
group, the Joint Meeting on Pesticide Residues, has
determined that glyphosate does not pose a cancer
risk to humans62.
There is also some community concern associated
with use of glyphosate on crops and entry into food
chain however these potential entry points do not
occur in the road corridor and hard edges of local
parks. There is little evidence of this risk in NZ and
appears to be associated with crops that are
3
genetically modified to be resistant to glyphosate -
this means such crops remain unaffected when
glyphosate has been applied. This potential
exposure pathway is not relevant in NZ as no
genetically modified crops are grown commercially
in NZ63.
The EPA notes that the current opinion of relevant
US, Canada, EU and Australian government
authorities is that glyphosate is safe to be used as a
herbicide. The EPA actively monitors the status of
glyphosate and international developments. If
needed it may initiate a reassessment after
reviewing the overseas reports (including WHO, the
US EPA and European Union64.
Biological
Biocontrol is not suited to control weed species typically occurring on
A study into 43 agents released
The risk of adverse impacts to the environment is low.
Biocontrol agents rarely pose any risks to humans
control
hard edges of local parks and many species in the road corridor65.
between 1972 and 2013 showed an
Before a new biological control agent is released,
due to the stringent, pre-cautionary assessment and
average cost of developing an agent
approval from the EPA is needed and all proposed
registration process.
Used to control
It relies on the weed’s natural enemy being free to grow, and in most
for New Zealand was NZ$355,686
agents are rigorously tested to assess the risk of damage
suited species in
areas this would contravene the weed control standards of local parks
(with the average cost per novel agent
to non-target plants. They are also tested for disease and
sites across the
and roads. Biological control might mean that areas are not tidy and
being NZ$475,334, more than double
evaluated for any other unwanted interactions it might
region including
safe, or could cause a nuisance to neighbours or damage to fences.
the average of NZ$202,803 for repeat
have. A comprehensive cost-benefit analysis is also
regional parks.
agents)66.
carried out and the results of all these studies are
included in an application to the EPA. The application
Not currently used
then goes through a public comment period. 67
on the hard edges
of local parks or
All species approved for release must initially come into a
the road corridor.
containment facility until permission to remove them is
granted by MPI pending evidence of their correct identity
and freedom from any diseases or other unwanted
organisms. 68
1 http://www.openspace.org.nz/Site/Managing_your_covenant/Restoration_information/revegetating_gorse.aspx
2 http://www.doc.govt.nz/documents/science-and-technical/sap243entire.pdf
3 Staff experience and in-field observations
4 https://www.landcareresearch.co.nz/__data/assets/pdf_file/0003/77691/Privet_Biosecurity_factsheet_8.pdf
5 https://www.landcareresearch.co.nz/__data/assets/pdf_file/0007/77911/Ecology_pest_status_moth_plant_Araujia_hortorum.pdf
6 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
7 Tu,Hurd & Randall, 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas.
8 Based on current contract analysis by Auckland Transport staff
9 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
10 Tu et al, 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas
11 http://www.weedbusters.org.nz/weed-information/controlling-weeds/controlling-pest-herbs-ground-covers
12 Tu et al, 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas
13 http://www.nzpcn.org.nz/page.aspx?conservation_habitat_protection_weed_control
14 Auckland Regional Council Weed Control Manual 2008
15 https://www.landcareresearch.co.nz/__data/assets/pdf_file/0018/39042/weed_management_handout.pdf.
16 Auckland Regional Council Weed Control Manual 2008
17 Tu et al, 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas
18 Distance provided by Auckland Transport
19 Staff experience and in-field observations
20 Staff experience and in-field observations
21 http://www.regional.org.au/au/asa/1998/6/315hewitt.htm
22 Auckland Transport and their contractors receive complaints from neighbours due to the high noise level during control work using this method – this has resulted in limited hours for operations in residential areas
23 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
4
24 Staff experience and in-field observations
25 Diesel engine exhaust is a category 1 carcinogen (Carcinogenic to humans) and petrol engine exhaust is a category 2B carcinogen (Possibly carcinogenic to human); Agents Classified by the IARC Monographs, Volumes 1–112 and
http://monographs.iarc.fr/ENG/Classification
26 Distance provided by Auckland Transport
27 Staff experience and in-field observations
28 B. De Cauwer et al, Efficacy and reduced fuel use for hot water weed control on pavements, Weed Research, 55(2), 195, 2015.
29 Auckland Transport and their contractors receive complaints from neighbours due to the high noise levels during control work using this method – this has resulted in limited hours for operations in residential areas
30 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
31 Extrapolation by Auckland Transport staff Based on current contract analysis
32 Staff experience and in-field observations
33 http://eap.mcgill.ca/MagRack/JPR/JPR_27.htm
34 Diesel engine exhaust is a category 1 carcinogen (Carcinogenic to humans) and petrol engine exhaust is a category 2B carcinogen (Possibly carcinogenic to human); Agents Classified by the IARC Monographs, Volumes 1–112 and
http://monographs.iarc.fr/ENG/Classification
35 http://www.nzpps.org/journal/55/nzpp_552070.pdf
36 Agpro Bio-safe MSDS
37 Distance provided by Auckland Transport
38 http://www.nzpps.org/journal/52/nzpp_520010.pdf
39 http://www.waitakere.govt.nz/abtcnl/ct/pdf/envrmntl/110602ag.pdf p.51
40 New Zealand Novachem Agrichemical Manual, 2013
41 New Zealand Novachem Agrichemical Manual, 2013
42 http://www.nzpps.org/journal/58/nzpp_581570.pdf
43 http://www.waitakere.govt.nz/abtcnl/ct/pdf/envrmntl/110602ag.pdf p.47
44 PWC – Weed Management Cost Review, Auckland Transport, 15 September 2015.
45 New Zealand Novachem Agrichemical Manual, 2013
46 New Zealand Novachem Agrichemical Manual, 2013
47 Agpro Bio-safe MSDS
48 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
49 Distance provided by Auckland Transport
50 New Zealand Novachem Agrichemical Manual, 2013
51 New Zealand Novachem Agrichemical Manual, 2013
52 New Zealand Novachem Agrichemical Manual, 2013
53 Graeme Bourdot, AgResearch, Auckland Council Weed Management Workshop 18 June 2015.
54 PWC – Weed Management Cost Review, Auckland Transport, 15 September 2015.
55 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
56 PWC – Review of weed control costs for hard edges in parks, 6 November 2015.
57 New Zealand Novachem Agrichemical Manual 2013
58 Glyphosate 360 Material Safety Data Sheet (MSDS)
59 New Zealand Novachem Agrichemical Manual, 2013
60 http://weedscience.org/summary/resistbyactive.aspx
61 IARC Monographs Volume 112: evaluation of five organophosphate insecticides and herbicides
62 http://www.epa.govt.nz/hazardous-substances/pop_hs_topics/glyphosate_learn/Pages/Glyphosate_regulation.aspx
63 http://www.foodsmart.govt.nz/whats-in-our-food/genetically-modifed-food/overview/
64 http://www.epa.govt.nz/hazardous-substances/pop_hs_topics/glyphosate_learn/Pages/Glyphosate_regulation.aspx
65 Staff experience and observations
66 Landcare Research, Paynter QP, Fowler SV, Hayes L, Hill RL 2015. Factors affecting the cost of weed biocontrol programs in New Zealand Biological Control 80: 119–127.
67 http://www.landcareresearch.co.nz/science/portfolios/managing-invasives/weeds/biocontrol/education/biocontrol-information/biocontrol-safety
68 http://www.landcareresearch.co.nz/science/plants-animals-fungi/plants/weeds/biocontrol/approvals .
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