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

Weed management
Table 8.2 Common weed management problems
and potential strategies
Example weed(s) Herbicide option(s) Comments
Wild radish, wild turnip and
shepherd’s purse
TT canola
or
Clearfield ® canola
or
Roundup Ready ® canola (see Note 1)
Barley grass, brome grass Selective grass (fop and dim – Group A)
herbicides, many options
or
Roundup Ready ® canola.
Vulpia
Subclover, medics, certain
thistles and capeweed
Trifluralin in standard canola
or
TT canola ± trifluralin
or
Roundup Ready ® canola
clopyralid
Watch herbicide residues
Identify paddocks clearly
Include as part of an IWM plan
Monitor for herbicide
resistance
High risk if already used more
than 6-8 times
Trifluralin efficacy improves
with better incorporation
Subclover and medic can be
very dense in dry sown ley
paddocks
Wireweed / black bindweed trifluralin and/or Clearfield ® canola Use both if weed pressure high,
otherwise avoid paddock
Wild oats
Group A-B resistant ryegrass
Toad rush
tri-allate
or
Roundup Ready ® canola
trifluralin and/or TT canola
or
Roundup Ready ® canola
TT canola
or
Dual Gold ® post-sowing, pre-emergence
Add trifluralin if annual
ryegrass present
Do not treat dense infestations
Consider fallow or forage crop
Competes strongly for available
nitrogen in wet seasons
Note 1: Where TT canola is mentioned, a mix of atrazine and simazine is assumed. Where Clearfield ® canola is mentioned, use of OnDuty ® or
Nufarm Intervix ® herbicide is assumed. Where Roundup Ready ® canola is mentioned, use of Roundup Ready ® herbicide is assumed.
Note 2: See herbicide labels for full spectrum of control, potential for tank mixes and application instructions for each herbicide.
Growing herbicide-tolerant canola is a key
management strategy to manage Group A and
Group B-resistant annual ryegrass in cereals.
Photo: C. Preston, University of Adelaide
on the species present and their resistance status.
Table 8.2 shows examples of some common problem
weeds and options for herbicide control.
Trifluralin
Research has shown that trifluralin can reduce density and
early growth of emerging canola plants if crops remain
stressed over a prolonged period (more than seven weeks
after sowing). However, the advantages in weed control will
normally compensate for any potential early damage caused
by sub-optimal application practices.
Trifluralin can be applied using the ‘incorporate before
sowing’ (IBS) technique which calls for low trash levels
and a fine soil tilth. The herbicide is incorporated with two
cultivations, the second of which is a cross-working.
Increasingly, trifluralin is being applied using the
‘incorporate by sowing’ technique, which enables its use in
no-till, direct drill and minimum till seeding. Plant residues
such as stubble will bind trifluralin and reduce the amount of
herbicide available for weed control. This is one reason why
direct sowing use of trifluralin has higher rates than when it
is used in a prepared seedbed. See label for details.
Continued use of trifluralin has led to the evolution
of trifluralin resistant annual ryegrass and an increase in
weeds not well controlled by this herbicide. Growers and
advisers need to plan carefully to avoid trifluralin resistance
developing, particularly when the weeds are already resistant
to the Group A and B herbicides.
Triazine herbicides
Triazine herbicides are best applied as a split application,
firstly before crop emergence and again when the crop and
weeds have emerged. This lessens the risk of crop damage
that would occur from applying the full rate before crop
emergence and also helps control a wider range of weeds
for a longer period.
Simazine or atrazine
Simazine must only be used pre-emergence, while atrazine
can be used pre and post-emergence. Normally, a mix of
simazine and atrazine (1–1.5 L/ha of each) is used preemergence
to broaden the spectrum of weeds controlled.
Also, simazine is less soluble and therefore less prone to
leaching through the soil. Only atrazine can be applied after
the crop has emerged.
Pre-emergence application
Applying the herbicide before the crop emerges gives better
control of annual grass weeds such as annual ryegrass.
Triazines can be applied up to one week before sowing.
n Pre-sowing – used where good rain has been received
and it is the start of the sowing window. Incorporation
42 Canola best practice management guide