Download Land for Wildlife — Notes series Environmental Weeds control

ENVIRONMENTAL WEEDS – CONTROL
METHODS
Land for Wildlife Note No. 11
November1999
LAND
FOR
WILDLIFE
VOLUNTARY WILDLIFE CONSERVATION
Author: Stephen Platt
Adapted by: Darryl Porshe for the Land for Wildlife program south-east Queensland
Weeds can threaten the integrity and long-term survival of wildlife
habitats. Whilst many of the species of plant that are pests to
agriculture have been intensively studied, this is not the case for most
weeds of bushland – ‘environmental weeds’. Thus, few chemicals
have been tested and registered for the control of plants that invade
bushland areas. This situation may improve when chemical
manufacturers and bushland managers realise the severity of problems
caused by some environmental weeds in areas managed for nature
conservation. Nevertheless, there are a variety of options available
for the control of environmental weeds. Thoughtful application of
these techniques to particular problem plants and careful
experimentation to determine the most effective treatment(s) for
particular situations, will allow the majority of these weeds to be
controlled, at least to some extent. As a first step, when managing
bushland areas, ask yourself – is any management action necessary?
If the answer is yes, as it frequently will be in the case of environmental
weeds, then proceed cautiously, test and record your management
action thoroughly before widespread application.
• prevent other unnatural forms of disturbance
unless these are part of the management plan or
of natural occurrence.
Prevention
• the success of treatment. Are suitable control methods
available? To what extent are they successful?
Prevention of environmental weed invasion is the first defence. Weeds
are dispersed by natural and artificial carriers. Natural vectors include
movement by wind, water and by native animals (ie. attached to fur,
deposited in scats). Artificial carriers include vehicles, contaminated
soils, deliberate introductions of plants and soil for ornamental or
land management purposes (eg. soil stabilisation), livestock and
agricultural products (eg. hay). Many other human activities provide
opportunities for environmental weed dispersal. In short, weeds tend
to follow disturbance.
• ease of treatment. This is influenced by many factors including
the abundance of the species, its degree and rate of spread,
whether it is a large or small plant and whether it is rare or
abundant at the site.
In addition to dispersal to a new site, an invading plant must find
conditions suitable for germination and growth in competition with
other species. In the case of weed plants, disturbance, such as soil
cultivation, trampling by stock or fire, can be an important factor in
this establishment phase. Disturbance is a natural part of most
ecosystems and native animals will cause disturbance, such as soil
tillage. This may be to the advantage of some environmental weeds,
as well as being important to some native species.
There are some valuable actions that can be taken by landholders to
reduce the extent of environmental weed invasion:
• use local native species in all planting, including ornamental and
garden plants or use sterile plants of other origin or use species
that, because of their life history and ecological requirements, are
rated as low risk as environmental weeds; advise your local
nursery of your requirements. Consult with your local council for a
list of environmental weeds.
• keep soil of foreign origin and garden refuse (plant cuttings,
unwanted hanging baskets) away from areas managed for native
flora.
• place tracks outside bush areas and across slopes to minimise
soil erosion.
• restrict agricultural produce and products (eg. hay and other
feeds, pasture seeds and fertilisers) to areas away from native
vegetation.
• control foxes, cats and exotic birds.
• keep vehicles away from natural areas.
• protect edges of habitat adjacent to disturbed areas by planting
buffers of appropriate native species.
• prevent soil disturbance by livestock, humans and other animals.
• minimise clearing of endemic species.
Control
Having taken steps to prevent the introduction of new weeds, attention
can be turned toward controlling those that already exist. The first
step is to develop a plan of attack. Factors to consider include:
• the degree of ecological damage being caused by the weed.
Weeds that are causing major ecological changes should have
high priority (eg. domination of exotic species). Weeds that
change the structure or floristics of the area should have high
priority.
• the likelihood of long term control. Is control achievable? How
much time is available to spend on weed control annually,
seasonally?
• whether multiple species can be targeted. Several species may
be susceptible to a single treatment and could be targeted all at once.
• rehabilitation requirements. What is known about replacing the
habitat/area occupied by the target weed with suitable native
species? Lack of suitable rehabilitation methods may leave the
site vulnerable to further invasion by weeds.
• topography/landscape (eg. drainage line). Is there a creek or
temporary stream present? Is removing the weed going to cause
erosion of soil.
• potential negative impacts on fauna. Are fauna dependent on the
weed? What suitable native replacements are available? Are
these in propagation? Thickets of weeds may be providing
habitat for small birds and mammals.
• potential negative impacts on land management. Will removal
of the weed create land management problems that may be even
more detrimental to habitat values?
All of these factors will vary according to the range of weed species
on the property. It is probably just as important to begin with some
species that you think you can beat. All good land managers know
that it is an ongoing battle to control weeds, whether they are of
native vegetation or pasture, but that a high degree of control is
achievable with dedication and effort, as is evidenced by many fine
examples of weed-free pasture and native vegetation on properties
throughout south-east Queensland.
Monitoring
New weeds arrive frequently and areas once thought to be under
control may re-establish themselves. Therefore, regular checks are
required. The saying ‘a stitch in time saves nine’ is very true of
weeds (environmental or otherwise).
Advice on declared and environmental weed control can be obtained
from: Department of Natural Resources – Land Protection Officer,
the Queensland Herbarium or your local Land for Wildlife extension
officer.
Published with the assistance of Bushcare — a program of the Commonwealth Governments’ Natural Heritage Trust
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WARNING: For personal safety, and to avoid contamination of the environment, extreme care should always be exercised when using
chemicals. The manufacturers instructions, printed on the chemical label, should be read and followed carefully. Manual methods of
environmental weed control, which avoid the use of chemicals, are preferable if there is a choice of technique. However, in many
situations for practical reasons or maximum effectiveness, chemicals may offer the best assistance.
ENVIRONMENTAL WEED CONTROL – CHECK YOUR OPTIONS
This chart summarises a range of control techniques. Determination of the best technique to apply requires detailed knowledge of the plant’s
life history and ecology. For further information contact the Department of Natural Resources – Land Protection Officer or your local Land
for Wildlife extension officer.
Method
Explanation
Suitable for controlling
Methods not involving chemicals
Mechanical methods
Manual removal
The weed is removed by hand-pulling or grubbing. Implements such
as a broad knife, trowel, secateurs, loppers, hatchet or small saw
may be helpful to remove specimens and underground parts that
may re-shoot. In the Bradley Method, less dense infestations are
treated first. Seedlings may be vulnerable where adults are not.
Undertake during wettest time of the year when the soil is moist. Be
aware that soil disturbance may encourage weeds.
Suitable for a wide variety of life forms.
Trees, shrubs, vines, herbs, etc. (eg.
Broad-leaved pepperina Schinus
terebinthifolia –(seedlings), Balloon
vine Cardiospermum grandiflorum).
Lopping
Weeds are removed with an axe, scythe, chainsaw, brushcutter, saw
or similar cutting implement. Not recommended for species with
underground tubers or bulbs.
Trees, shrubs and vines
(eg. Cocus/queen palm Syagrus
romanzoffiana.)
Ringbarking
The bark is peeled away or cut through and the sapwood (outer,
often lighter-coloured wood) is cut, around the entire girth of the
plant, preventing nutrient and water flow in the stem. Ringbarking
should be done beneath any branches and close to the ground (to
limit re-shooting).
Trees, shrubs and vines. (eg. Pine Tree
Pinus spp.).
Scarifying
The top few centimetres of soil are removed using a suitable tool such
as a fire hoe. The aim is to remove soil-stored seed. Do not leave
disturbed area open for reintroduction of weeds.
For small patches of soil dominated by
weeds. (eg. Singapore daisy Wedelia
trilobata and Fishbone fern
Nephrolephis cordifolia).
Ecological tolerance
methods Fire-sensitive
species
Fire-sensitive species may be killed by burning the vegetation. Some
species may be susceptible for only part of their life or annual cycle.
As many native plant associations are adapted to fire (of certain
frequency) and are fire-tolerant, introduced weeds may be selectively
removed. Some native species are fire sensitive. If the frequency of
burning is too high, native plants may be unable to produce seed
before the next fire or juveniles may be killed. Be aware that some
weeds can be promoted by fire. Always trial new techniques before
widespread application. Burn only when a permit has been granted
and consult your local rural fire brigade for information and
assistance.
Lantana Lantana camara – not
recommended in some wooded areas
and use fire as precursor to herbicides.
Fire-seed bank
This method exploits the differences in seed maturation that occur
between plant species. Burning vegetation whilst seed is developing
or semi-ripe on a weedy species may eliminate the weed species
production of seed for that year. Timing is obviously critical. This
technique may severely affect annuals because of their dependence
on a single crop of seed. Perennials and native species that are able
to re-shoot and produce seed later in the season may be benefited. In
practice this technique is limited by the extent of the burn (some
areas can remain unburnt), the amount of soil-stored seed, the variation
in seed maturity within a species and the ability of the species to
recolonise the area. Most annuals have excellent dispersal
mechanisms designed to get around their vulnerable life cycle. Other
desirable species may be affected. Fire frequency is limited by the
capacity of the native vegetation association to withstand fire of the
frequency. For example, native grassland plants may withstand fires
every 2-4 years whereas a dry forest may be intolerant of fires that
occur more frequently than once every 30-60 years (on average).
Obligate seed regenerators. An option
when numbers of weeds are too large for
alternative methods. Note that follow-up
treatments are often required. (eg. Year 1
– burn, Year 2 – chemicals. There may
be insufficient fuel in Year 2 to burn).
Removal of seed heads
Seed can be collected by hand from undesirable species. The aim is to
exhaust the seed supply. A lawn mower, whipper-snipper, sicklebar mower or tractor-driven slasher may be used to remove seed
heads of undesirable species that are exposed by their naturally taller
stance or rapid recovery after fire.
Exotic grasses. (eg. Green panic
Panicum maximum, Johnson grass
Sorghum halpense.)
Produced by the Land for Wildlife program south-east Queensland
November 1999
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Method
Explanation
Suitable for controlling
Methods not involving chemicals
Overlay
Old carpet, carpet underlay, a thick layer of newspapers, steamed
eucalypt mulch or black plastic is used to prevent sunlight reaching
the weed-infested soil. A large number of commercial weed
suppressants are now manufactured to help eliminate weed growth.
Alternatively, the ground is watered and covered with clear plastic,
which is pegged down. The plastic acts as a glasshouse germinating
all seed in the soil. After time the water supply is exhausted and the
plants die. Can be combined with manual removal or chemical
treatment. Only suitable for small weedy patches. All species are
killed in the patch. Has been successfully used to establish a species
by planting the site with a densely spaced stand of the species.
Overplanting
Dense stands of native shrubs and trees are established to shade-out
weeds. Desirable ground flora may also be adversely affected.
Short and prostrate (groundhugging)
plants. (eg. Balsam, Impatiens spp.,
Siratro, Microptilium atropurpureum,
Fishbone fern Nephrolepis cordifolia,
Creeping
lantana
Lantana
montevidensis, Brazillian nightshade
Solanum seaforthianum, Thunbergia
spp.)
Chemical Methods *
Chemicals* can be dangerous to humans, may be directly toxic to wildlife or pass through the food chain and be accumulated to toxic levels.
Care must be taken to avoid contamination of water for human consumption. Direct application techniques can minimise the amount of
chemical used, increases the capacity to directly affect the targeted species and is often more effective in eradicating the undesirable plant.
ALWAYS follow manufacturer’s labels, read warnings and, if in any doubt, seek advice. Always wear protective clothing. Non-chemical
methods avoid these potential risks but chemical methods are widely practised mainly for practical reasons. Detailed information about the
use of chemical methods should be sought from the Department of Natural Resources and is deliberately not given here. Avoid dormant
periods. For example, many northern hemisphere plants of cold climates ‘shut down’ over winter months and, due to limited sap flow, are
less vulnerable to treatment by herbicide at that time. The plant must be actively growing for the most effective results.
Cut stump
The weed plant is lopped and the exposed surface of the stump
painted with a herbicide*. The application of herbicide should occur
within 15 seconds to ensure the absorption of the chemical through
the plant system.
Stem injection (Drill &
Fill)
A hole is drilled at a downward slope into the trunk of the plant.
The hole is filled with (usually undiluted) herbicide* and plugged.
Injection under pressure is sometimes most effective, particularly
for plants containing high levels of sap, such as exotic coral trees.
‘Frilling or Chipping’
The bark and sap-wood are ‘frilled’ (also called chipping) using a
small axe and the cups produced are immediately filled with undiluted
herbicide.
Bark stripping / stem
painting
The bark surface is peeled away and the exposed wood is treated
with an appropriate herbicide*.
Wild tobacco Solanum mauritianum,
Castor oil plant Ricinus communis.
Foliar application –
spray unit
The leaf surface is sprayed with an appropriate herbicide*.
Johnson grass Sorghum halpense,
Green panic Panicum maximum.
Foliar application – wick
wiper
Leaf surface is wiped with a wick soaked in undiluted herbicide*.
Broad leaf privet Ligustrum lucidum,
Camphor laurel Cinnamomum
camphora, Cadaghi Corymbia
torelliana, Chinese elm Celtis sinensis,
Broad leaved pepper Schinus
terebinthifolius.
Other methods
A third method of control involves targeting species interactions. Biological control methods may offer potential to control some environmental
weeds such as Lantana camara. Consult the Department of Natural Resources for further information.
Combined methods / species interactions
Combinations of the above methods may be required to reduce the population of an environmental weed to a satisfactory level. Combined
methods can target several vulnerable stages in the life cycle. Interactions between animals and plants must be considered. Removing all the
Lantana camara from an area may result in a loss of habitat for smaller birdlife. Target a smaller area than you think you can deal with annually
in the first year. Follow-up years may require more effort.
Disposal
Care in disposal of environmental weeds is essential to prevent harvested material becoming a source of new weeds. Composting at high
temperatures and burning can be used. Consult your local council before disposing of weed material at a refuse depot. If allowable, material
taken to a refuse depot should be sealed in a bag. Avoid giving weeds to animals as feed (eg. chooks), since this may be a means of dispersal,
unless you are sure the plants are sterile.
Repetition
Many weeds will survive single treatments and will require follow up treatments. Soil stored seed and propagules blown in by the wind will be
a continuous source of new weeds. Control in unison with neighbours is highly recommended.
Identification
Ensure you have correctly identified the plant as a weed BEFORE you attempt to control it.
*See warning about the use of chemicals on page 2
Produced by the Land for Wildlife program south-east Queensland
November 1999
page 3
Four Environmental Weed Profiles
Lantana Lantana camara
Lantana is a thicket-forming shrub to 3
metres high, with lots of prickly stems.
Flowers can vary from pale cream,
white, pink, orange, red or purple and
can be found during most of the year.
Lantana is native to the tropical and subtropical regions of Central and South
America. It is found throughout most
coastal and sub-coastal areas of eastern
Australia, from north Queensland to
southern New South Wales. Lantana grows in a wide variety of
habitats, from exposed dry hillsides, to wet heavily shaded gullies.
Ripe fruits are fleshy and black, and are usually dispersed by birds.
One single plant can produce up to 12000 seeds per year. Lantana
can be grubbed or pulled, followed by regular mowing or spot
spraying to control seedlings. Adult plants may be eradicated using a
cut stump or basal bark treatment. Fire may be used, however followup herbicide treatment will most likely be required.
NATIVE ALTERNATIVE
Orange Thorn (Citriobatus pauciflorus), Poison Peach (Trema
tomentosa) Wild May (Leptospermum polygalifolium), Hairy
Bush Pea (Pultenaea villosa) or Native Lasiandra (Melastoma
affine).
Madeira Vine or Lamb’s Tails or Potato Vine
Anredera cordifolia
Madeira vine is a native of South America,
introduced into South-east Queensland as
an ornamental plant. A succulent, leafy,
twining vine up to 8 m tall, regrowing from
underground tubers and reproducing by
aerial tubers along the stems. Vegetative
reproducers are dispersed by gravity or
water. Leaves are light-green, 4 to 5 cm
wide, heart-shaped and fleshy. To flower,
the Madeira vine requires high levels of
sunlight. The flowers are recognisable as
small, white, fragrant and in drooping
masses in summer, whilst the fruits are very rarely seen but known to
occur in South-east Queensland. Physical control includes: cutting
and pulling down stems and aerial tubers, dig tubers from the ground
and carry all away for burning or disposal at a council refuse site (not
as green waste). Chemical control includes spot spraying actively
growing plants with herbicide. Follow-up sprays are required to treat
regrowth. There is no registered chemical control.
NATIVE ALTERNATIVE
Tape Vine (Stephania japonica) Wonga Vines (Pandorea
spp.), Native Clematis or Kennedia spp., Native Jasmines
(Jasminium spp.) or Native Hoya or Wax flower (Hoya
australis).
Broad-leaved Privet or Tree Privet Ligustrum
licidum
Broad-leaved Privet is a native of China and
Japan and is a ‘garden escapee’. A perennial
shrub or small tree, it can grow up to 10
metres in height. Its leaves are oval, hairless,
leathery, between 5-13 cm long, has a
pointed tip and appears on opposite pairs on
the stem. Flowers are small, white and occur
in bunches up to 20 cm long. Fruit are black or blue berries
approximately 8 mm in diameter. Privet has a very high reproductive
rate. It flowers only where foliage is exposed to sunlight and can
produce up to one million seeds per plant, of which greater than 90%
are viable. Birds eat the ripe fruit and can distribute seeds long
distances from the parent plant. Seedlings can be hand pulled or
mowed. Plants can be eradicated by either foliar spraying, basal
barking, cut stump or stem injection treatment using a registered
chemical.
NATIVE ALTERNATIVE
Hard Quandong (Elaeocarpus obovatus) Lilly Pilly (Syzygium
spp.), Melaleuca spp., Grevillea spp. or Lemon Myrtle
(Backhousia citriodora).
Chinese Elm Celtis senensis
Chinese elm is a native of China, Korea
and Japan. It is a deciduous tree, which
can grow to heights greater than 10
metres. Its leaves are broad, egg shaped
with an offset base and scalloped
margins. Flowers are inconspicuous and
produced at the same time as the new
leaves in late winter. Fruit are globular,
shiny, dark orange and 7-8 mm in
diameter. Commonly, the seeds are
spread by birds. Hand pulling or
chipping out with a hoe when small are the most effective controls.
Seedlings can be foliar sprayed, whilst older plants can be eradicated
using the cut stump method. Follow-up monitoring should always
be conducted.
NATIVE ALTERNATIVE
Three-veined Cryptocarya (Cryptocarya triplinervis) White
Cedar (Melia azedarach), Native Celtis (Celtis paniculata),
Tulip Wood (Harpullia pendula) or Rose Almond (Owenia
venosa).
Please Note:
The native alternative species listed are a general guide
only. Promote natural regeneration or replant using local
endemic species where available.
Acknowledgment:
Text and selected illustrations relating to this technical note was sourced
from the Department of Natural Resources and Environment, Victoria:
Land for Wildlife Program.
References and further reading:
Australian National Parks and Wildlife Service. (1991) Plant Invasions:
The Incidence of Environmental Weeds in Australia, ANPWS, Canberra.
Bradley, J. (1988) Bringing Back the Bush. Landsdowne Press, Sydney.
Buchanan, R. (1989) Bush Regeneration – Recovering Australian
Landscapes. TAFE NSW, Sydney.
Kleinschmidt, H. and Johnson R. (1987) Weeds of Queensland. DPI,
Brisbane.
Kleinschmidt, H., Holland, A. and Simpson, P. (1996) Suburban Weeds.
DPI, Brisbane.
See Land for Wildlife South-east Queensland Note No. 1 “Reference List”
for further reading and references.
Produced by the Land for Wildlife program south-east Queensland
November 1999
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