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

Weed management
of the herbicide to a depth of 5 cm will improve control.
Full disturbance sowing can be used to incorporate the
herbicide.
n Post-sowing – relies on rain (20–30 mm) following
spraying to move the herbicide into the soil. Weed control
levels will be lower if no rain falls for 3–4 weeks. This
method is often used where large areas of canola are to
be sown and for minimum till situations.
Post-emergence application
An adjuvant is added to atrazine to increase absorption of
the herbicide into weed leaves. The post-emergence split
improves the control of broadleaf weeds.
Effect of dry conditions
Triazine herbicides are primarily absorbed through plant
roots, particularly in grasses. If not incorporated pre-sowing
the herbicide will remain on the soil surface and will gradually
vaporise until rain washes it into the soil. Weed control will
be poor as weeds can emerge through the herbicide.
Dry conditions will also increase the plant-back period
for sensitive crops because soil moisture is needed for the
herbicide to fully decompose.
Plant-back periods
Triazine herbicides are persistent in alkaline soils (pH Ca
> 7.0).
For these soils, limit the total rate of triazine herbicides to
2 L or 1.1 kg granules per ha. Read the herbicide label for
application rates and check plant-back periods as a part of
the rotational plan for the paddock. If the TT canola crop
Effects of accidental spraying of the wrong herbicide on
the wrong variety. Here the Clearfield ® herbicide OnDuty ®
was sprayed onto a conventional variety.
Photo: P. Lockley, NSW DPI
fails following application of the triazine herbicide, only crops
tolerant to these herbicides can be sown. Sowing time
may be too late for lupins or faba beans. In northern NSW
cropping systems fallowing through to sorghum or maize
would be the safest option.
Note that the triazine herbicides will kill conventional,
Clearfield ® and Roundup Ready ® canola. Ensure that
paddocks are correctly identified, particularly for spray
contractors.
Clearfield ® varieties
Clearfield ® (imidazolinone [IMI] tolerant canola) varieties are a
suitable option in some paddocks. Clearfield ® varieties have
a similar weed control spectrum to the TT varieties, although
the main weakness is capeweed. However, caution in their
use is needed because Group B herbicide resistance is
widespread.
In acidic soils, the breakdown of IMI herbicides is slower
than in neutral or alkaline soils. Read the herbicide label and
check plant-back periods as part of the rotational plan for
the paddock.
Note that OnDuty ® and Intervix ® herbicide will kill
conventional, TT and Roundup Ready ® canola. Ensure
that paddocks are correctly identified, particularly for spray
contractors.
Roundup Ready ® varieties
Roundup Ready ® (glyphosate-tolerant canola) varieties
are a suitable option in some paddocks. Glyphosate is a
broad spectrum herbicide providing good control of grass
weeds and of many, but not all, broadleaf weeds. Only
Roundup Ready ® herbicide is registered for use. Glyphosate
can only be applied up to the six-leaf stage otherwise crop
damage could occur. Read the herbicide label and follow the
crop management plan. Remember that glyphosate used
alone will not control Roundup Ready ® canola volunteers
that germinate over summer or autumn after crop harvest.
If using glyphosate for summer herbicide or knockdown
application mix another herbicide at a rate that will control
canola volunteers. Follow the crop management plan.
Note that Roundup Ready ® herbicide will kill conventional,
Clearfield ® and TT canola. Ensure that paddocks are
correctly identified, particularly for spray contractors.
Dry sowing
Only dry sow paddocks with potentially low weed numbers.
Dry sowing conditions prevent pre-sowing knockdown
(for example, glyphosate) weed control. When rain falls after
sowing dry, weeds and crop emerge together and significant
yield loss may occur before it is possible to control the
weeds.
Soil active herbicides will not be effective under dry soil
conditions and have the potential to allow some weeds to
grow through the herbicide layer.
Trifluralin will not activate in dry soil, remaining tightly
bound to soil particles. If the trifluralin has been well
incorporated it will remain in the soil for several weeks until
Canola best practice management guide
43