Bushland Weeds Manual - Environmental Weeds Action Network

Chapter 8 Herbicide Use in Bushland
• Select herbicide and rate most effective at
controlling the weed and with least damage to
environment (selective, non-residual, low toxicity to
humans and other organisms, lowest effective rate).
Residual herbicides (metsulfuron methyl, picloram)
can remain active in the soil for up two years,
which can affect the growth of susceptible native
plants over the period. Soil-mobile residuals could
also contaminate waterways. However, for some
weeds it may be more sensible to use a higher rate
and/or a more toxic or more residual herbicide than
an ineffective treatment that requires repeated
application and does not remove the weed threat.
• Understand the hydrology of the system that is
being treated. The likelihood of run-off into
waterbodies and/or leaching into the water table
must be assessed. If necessary, establish ‘no
spray’ zones. Only use herbicides that have been
specially formulated to have minimal impact on
aquatic organisms. Don’t add surfactants or
wetting agents to such formulations as these are
often more toxic to many aquatic organisms than
the active ingredient in the herbicide. Use
herbicides with low soil mobility where possible.
• Establish a mixing area (easy access, no desirable
species, not subject to erosion or run-off, rarely
visited by public or workers).
• Use a dye to minimise missed areas and avoid
over-spraying.
• Always apply at the most appropriate time
(ineffective application results in failure and
unnecessary use of herbicide in bushland).
• Monitor effects of treatment on the whole plant
community using a transect or quadrat-based
approach which quantifies the number and cover
of native plants. Native plant species include more
than just trees and shrubs. Monitoring must
include annual and perennial herbs, geophytes and
grasses whose loss from the plant community
should not be overlooked.
• Identify mistakes and if necessary improve your
method. Monitor the effects of treatment on the
weed quantitatively. Use the same transects or
quadrats set up for monitoring the plant
community. At the very least, keep a record of
plants/area treated, the herbicides and rate used,
date and conditions.
• Always follow up weed control work. If treatments
are not followed up with further spraying or handweeding
of overlooked or surviving plants, the
initial treatment becomes a waste of resources and
a pointless introduction of herbicide into the
environment.
Using contractors
There is some concern about contractors entering the
field with insufficient training in the application of
herbicides within bushland situations. Contractors
unsympathetic to bushland conservation are more likely
to damage native plants through trampling,
misidentification, or over-spraying. The contractor you
select should have knowledge of the flora and an interest
in bushland flora and fauna as well as an understanding
of the chemicals used, the way they work and the weeds
they control. They should be willing to use backpacks,
hand held sprayers, or wiping devices when required.
Such contractors are rare and in high demand
throughout the peak weed season. At present, there are
few suitable contractors available. The Australian
Association of Bush Regenerators (Western Australia)
(AABR (WA) Inc) has a list of those contractors in the
Perth area that have sufficient experience to undertake
bushland work. This list is available from AABR (WA)
Inc., PO Box 1498, Subiaco, 6904. Ask around, get second
opinions and if you are not happy with someone’s work
be sure to let them know why!
Make sure the spray contractor you hire and their
employees have the appropriate training. Spray
contractors must work for a business registered with
the Pesticide Safety Section (PSS) of the Health
Department of Western Australia (Ph: 08 9383 4244).
A person with a provisional licence can carry out
spraying as long as a person holding a full licence
supervises them. Any person operating a pesticide
spraying company must hold a full licence.
To get the most for your money and the best job
done, it is important to have weed maps and a
contract. The contract (Appendix 1) outlines the work
to be done and ensures that if the job is not done
satisfactorily you are in possession of a written
agreement. The Weed maps are multi-purpose, they
allow you to show the contractor the location of the
weed populations; walk around the bushland with the
contractor and relate populations to those on the
map. By supplying the contractor with the weed map
before the job, they are more easily able to relocate
each population. The map also provides a monitoring
tool that allows you to assess the reduction in
population area and ensure no populations are
overlooked by the contractor. In combination these
two documents are invaluable (Box 8.2).
Some herbicides used in bushland
All applications and concentrations quoted in this
manual are intended as an illustrative guide. They are
covered by minor use off-label permit number
PER4984, which is only valid for Western Australia.
Some useful herbicide terminology:
• Contact – kills only plant tissue to which it has
been applied. Old or well-established annual plants
may grow back after such treatments.
• Systemic herbicide – penetrates plant cells and
moves through the plant from shoots to roots in
the phloem.
• Broad spectrum – kills a wide range of plants.
• Selective – kills only a particular type of plant, e.g.
grasses.
• Non-residual (knockdown) – kills existing plants
but has no effect on subsequent germinants.
• Residual – remains active in soil for some time
(may kill germinating seeds (pre-emergent) and
susceptible plants).
• Post-emergent – applied directly to established
plants and/or soil.
• Pre-emergent – applied to the soil before the weed
germinates, killing germinating seedlings (preemergent
herbicides will also kill susceptible
native seedlings).
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