Home' Smart Farmer : February 2012 Contents February 2012
By BRIAN SINDEL and MICHAEL
IVEN the estimated cost of weeds to
Australian agriculture of $4 billion
annually, the focus of weeds profes-
sionals and agencies is largely on the econom-
ic benefits of controlling them and maximising
They also focus on the legal requirements of
controlling prohibited or declared species and
issues of biosecurity.
Weeds constitute a significant cost in terms
of control and lost productivity, however they
also cause problems for the owners of small
Apart from the legal obligation to control
certain weeds, extensive weed outbreaks on
small farms may:
•Impact on biodiversity and human health.
•Spread to neighbouring land, including
production farms, which in turn may strain
•Cut significantly into niche-farming prof-
•Detract from time better spent on other
About 28,000 plant species have been intro-
duced into Australia since European settle-
ment. More than 2770 of these have become
naturalised and weedy, of which about 65 per
cent are considered a problem for natural
ecosystems and about 35pc are considered a
problem for agricultural systems.
Some weeds are declared under legislation
as requiring control by all landholders.
Experience shows that those farmers who
have a plan (deliberation), in which they inte-
grate several control methods (diversity), and
with which they persist over many years (ded-
ication), are the ones most likely to have suc-
cess in controlling weeds.
In applying this 3D approach, the two pri-
mary methods used by the majority of small
farm owners to control new weed outbreaks
are digging or pulling the weed out, and
spraying the weed with a herbicide.
However, there is also a variety of other
options for weed control. The control meth-
ods used will be dictated by the type or types
of weeds you are controlling (hence accurate
identification is important), their growth
stage, the size of the infestation, the situation
Landholders may undertake a variety of
identification measures when they find an
unknown or unusual plant on their property,
including: Asking a local professional, such as
a weeds officer or agronomist for advice, hav-
ing a weed identification book, using a web-
site or other reference materials, use a good
professional identification service or weeds
expert, ask a neighbour (particularly one who
is an experienced farm manager), other land-
holder or Landcare member for advice.
Why is time of year important for weed
•Each weed species has a particular life-
cycle, and time of year when it is flowering or
•It is important to detect and control weeds
early in their life-cycle before they produce
seed (there is a well known saying that 'one
year's seeding is seven years' weeding!').
•Some weed species are more noticeable at
certain times of year.
•Often you will have the best chance of
killing or controlling weeds, at least with her-
bicides, when they are young and actively
•Seasonal and climatic conditions, particu-
larly rainfall, influence the time of year when
Weeds constitute a significant cost in terms of
control and lost productivity, however they also
cause problems for the owners of small area
Legal obligation to control certain weeds
Methods used dictated by varieties
Good farm hygiene practices stop seed-set
weeds are most likely to grow quickly.
•Likewise, major disturbances that create
bare ground, such as floods, fire, cyclones,
drought and overgrazing, and even weed con-
trol activity (such as spraying of herbicide) can
contribute to weed infestation.
Which control methods are suitable for
small farm owners?
The best way to control weeds in a pasture
is to promote the growth of desirable pasture
plants so that they outcompete the weeds for
water, nutrients and light. This may involve
timely fertiliser application and/or irrigation at
the start of the active growth period of the pas-
tures. Where there is bare ground or gaps in
the pasture, weeds will thrive.
Consequently, these areas may need to be
resown with seed of vigorous pasture plants.
While most livestock avoid grazing unpalat-
able and toxic weeds in pastures, they can
sometimes be encouraged to be less selective,
and to eat and trample the less palatable non-
toxic species, by running them in paddocks in
large numbers for a short period of time.
Either a synthetic or natural organic mulch
can suppress weed growth in gardens,
orchards and other areas used to grow a vari-
ety of crops.
Mulches act to cut out light to germinating
seedlings, and provide a physical barrier to
There are two broad categories of herbi-
cides. 'Selective' herbicides will kill certain tar-
get weeds but cause little damage to other
weeds and certain desirable species. In con-
trast, 'non-selective' herbicides, such as the
commonly used glyphosate, will kill most
plants with which it comes in contact.
It is particularly important, therefore, when
using non-selective herbicides, to apply the
chemical only to the target weed to avoid
damage to surrounding vegetation.
• Need to know more?
Near and downwind of previous weed
Watercourses and dams, particularly after
Roadways and traffic areas.
Areas in which earthmoving and other
contractors have been working.
Boundaries with neighbours and along
Livestock camps and feeding areas.
Newly sown crop and pasture paddocks.
In remote or relatively inaccessible areas
(such as remnant bushland).
Near sheds, tanks, stockyards and other
Revegetation areas (e.g. tree plantings) and
gardens (particularly new gardens where
mulch or topsoil has been used).
Where to look
for farm weeds
help control $4b
problem of weeds
*This is an extract from Weed Detection on
Small Farms: A Guide for Owner by professor
of agronomy and soil science Brian Sindel,
from the School of Environment and Rural
Science, University of New England, co-
authored by Michael Coleman.
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