best practice management guide for south-eastern Australia - Grains ...

Weed management
Burning windrows can kill weed seed and reduce seedbank numbers.
Integrated weed
management
Herbicide resistance has evolved in about 25 weed species
in Australia. It should also be noted that a number of weeds
have evolved resistance to several herbicide mode-of-action
(MOA) groups. Some populations of annual ryegrass have
evolved resistance to all the selective MOA herbicide groups.
The ‘herbicide only’ approach to weed control is not viable
over the long term. Herbicide resistance is forcing a growing
number of producers to look at a longer-term approach to
weed control and introduce a range of non-herbicide tactics
to control weeds.
To maintain or increase the current level of cropping
intensity and diversity, effective herbicides are essential.
In order to keep herbicides effective, producers and
advisers must adopt a more integrated approach to weed
management.
Integrated weed management (IWM) is a system for
managing weeds over the long term, particularly for the
management and minimisation of herbicide resistance.
IWM incorporates the use of as many different weed
control techniques as possible within a farming system, with
a focus on preventing seed set of any weed escapes. In
certain situations, less profitable techniques may have to be
used in the short term to get longer-term control of weeds
and improved returns. An example of this in canola would be
windrowing the crop, followed with a knockdown herbicide
to prevent any weeds from seeding. Windrowed stubble
could also be burned to kill weed seeds.
Essential principles of an IWM program include:
Photo: C. Preston, University of Adelaide
1. Monitor levels of weed control.
2. Stop weeds from setting seed and thus keep seedbanks
small.
3. Use as many weed control tactics as possible, together with
good agronomy to grow competitive high yielding crops.
1. Monitor levels of weed control
As discussed earlier, weed control techniques do not give
complete control when used alone. Weed escapes need to
be identified and controlled before they set seed.
2. Stop weed seed set – keep weed
seedbanks small
The key to keeping seedbanks small is to prevent, or at
least greatly reduce, inputs of fresh seed. To achieve this,
it is important to aim for high levels of weed control using a
combination of control methods.
The ‘double knock’
No one tactic will control 100 per cent of weeds, so
introducing a second tactic (the second knock) to kill the
survivors of the first always gives the best control. The most
common example of this is a pre-sowing application of
glyphosate, followed by full cultivation sowing. The use of
no-till seeders removes this second knock so an application of
Spray Seed ® or paraquat 5–10 days after the glyphosate and
just prior to planting will control the survivors of the glyphosate
application. Using a pre-emergent herbicide followed later in
the season by a post-emergent herbicide can be considered a
double knock if targeting the same weed species.
Canola best practice management guide
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