A competitive canola crop can halve grass weed seed set, but in order to achieve that, growers need a vigorous variety, robust pre-emergent herbicide and the best agronomic package.
Trial work across six years in the southern growing region, with investment from the Grains Research and Development Corporation (GRDC), has demonstrated how important crop nutrition and time of sowing are for maximising canola vigour and yield.
EPAG research agronomist Andrew Ware said canola required 80 kilograms of nitrogen per tonne of grain produced.
"Growers will be rewarded if they set a target yield and fertilise accordingly," Mr Ware said.
"The other key factor is to sow early - in April, through to early May for some varieties, so that the start of flowering occurs in the optimal window."
Canola offers growers the opportunity to tick off all the WeedSmart Big 6 tactics for reducing the impact of herbicide resistant weeds - diversity in crops, mix and rotate chemistry, double-knock, competitive crops, stop seed set and harvest weed seed control.
However, growing hybrid canola requires higher management input to gain the full benefits of the higher investment in seed.
Hybrid canola varieties are generally very competitive against weeds, particularly when sown in the correct window and supported with a robust pre-emergent herbicide package to give the crop a head start.
Mr Ware said canola yield was optimised when the time of sowing resulted in the crop flowering and setting pods when there was minimal heat, moisture and frost stress.
"Growers now have the choice of hybrid canola varieties with several new trait combinations for weed control," he said.
"New traits and combinations available now or in the near future include stacked imi + triazine, glufosinate - triazine and glyphosate tolerance for weed control along with varieties with high omega 3 and non-shattering pod traits.
"Hybrid canola is now considered a reliable option for low rainfall areas when adequate nitrogen is applied."
When it comes to Roundup Ready (RR) canola, the key strategies are to use pre-emergent herbicide, sow early and apply the first glyphosate spray when the crop is at one to two leaf stage.
Sowing in the optimal window will often mean there is no opportunity for a pre-sowing knockdown.
"That means the timing of the first glyphosate application is strongly recommended at the one to two leaf crop stage, which is likely to occur while other paddocks are still being sown," Mr Ware said.
"If growers have decided to plant RR canola this season, they will already be aware of the stewardship agreement and the key requirement to a limit of two glyphosate applications per crop and applied before the crop reaches six-leaf stage for Roundup Ready canola and first flower (three applications are permitted) for TruFlex canola.
"Only glyphosate formulations that are registered for use on RR and Trulfex canola are permitted."
The value of herbicide tolerance traits in crops comes from their strategic use in a crop rotation and an understanding of the resistance profile of the weeds present.
Like any tactic, herbicide tolerance traits can be broken if they are over-used in a cropping system.
"There must be a plan in place to control survivor weeds and in RR crops, that means having strategies to take the pressure off glyphosate and preventing weed seed set.
In that instance, crop competition can play a crucial role by providing season-long suppression of weeds.
"Consider the other herbicide options in-crop, such as including a registered pre-emergent grass herbicide and mixing clethodim or Lontrel with the second glyphosate application," Mr Ware said.
"The non-shattering pod trait (Podguard) supports direct harvesting but this is going to be too late to stop weed seed set, and crop topping with glyphosate is not going to control any glyphosate resistant weeds present.
"Windrowing is a reliable tool for managing late germinated and resistant grass weeds, especially when coupled with a harvest weed seed control method such as an impact mill, chaff lining and the like."
Strategies also need to be in place to control herbicide tolerant canola volunteers, most of which will germinate in the following season.
