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

Weed management
Thoroughly cleaning
farm machinery can
reduce the spread
of resistant or
troublesome weeds
between and
within farms.
Photo: nicole baxter
Keeping seedbanks small reduces the chances of
resistant weeds being present when herbicides are applied.
This will vary with weed species and herbicide MOA group.
For example, with annual ryegrass the gene for Group B
resistance has an average initial frequency of 1 in 15,000,
making it common in annual ryegrass populations, while
the average initial frequency of the gene for glyphosate
(Group M) resistance is about 1 in one billion, making it rare.
A smaller seedbank also means a smaller potential weed
problem.
3. Use as many weed control tactics as possible
Effective crop competition is the start of good weed control.
Choosing the best adapted variety and sowing quality seed
on time at the optimum depth for the conditions with the
best nutrition gives all weed control tactics a head start.
Tactics suitable for weed control in canola include:
n Burning previous crop residues to kill weed seeds. This
must be planned before harvest of that crop.
n Herbicides:
n knockdown;
n pre-sowing;
n post-emergent; and
n harvest-aid or salvage spray – as long as weed seed
set is controlled.
n Wick wiping – applying glyphosate through a wiper to
control weeds that are taller than the crop.
n After harvest – applying a knockdown herbicide for late
emerging and maturing weeds
n Green or brown manure – where there has been a ‘blowout’
of herbicide resistant weeds.
n On-farm hygiene – sow weed-free seed, clean machinery
Table 8.3 Weed control options other
than selective herbicides
Crop system
1
2
3
4
Additional weed control options
Pre-sowing control, competitive crops, burning header trails
and weed seed collection at harvest.
Pre-sowing control, competitive crops, burning header trails,
weed seed collection at harvest, and crop topping of pulse
crops.
Pre-sowing control, competitive crops, burning header trails,
weed seed collection at harvest, crop topping of pulse crops
and silage/hay production or brown/green manuring.
Pre-sowing control, competitive crops, burning header trails,
weed seed collection at harvest, crop topping of pulse crops,
silage/hay production or brown/green manuring and pasture
topping, grazing management, ‘winter cleaning’ and fallow.
before entering property or from paddock to paddock,
weed-free fence lines and roadsides.
The more diverse the crop system, the more applicable
the cultural options become. Below are four possible crop
systems:
1. Cereal-canola-cereal-cereal-canola
2. Cereal-canola-cereal-pulse-cereal-canola
3. Cereal-canola-cereal-pulse-forage-cereal-canola
4. Pasture-pasture-pasture-canola-cereal-pulse-cerealpasture-pasture-pasture.
Crop system 1 is used more often than the more diverse
systems because of its higher short-term returns. However,
the more diverse systems, especially those including a
forage or pasture phase, have the longer-term benefit of
a lower risk of developing herbicide resistance and more
opportunities to control weeds. Table 8.3 demonstrates that
more diverse cropping systems allow for a wider range of
weed control tactics, particularly non-herbicide tactics.
46 Canola best practice management guide