Weed control options for SA grown canola - Elders Rural Services

Weed control options for SA grown canola

Weed control options for the South Australian canola industry have evolved significantly over the last 12 months, following the 2020 approval of TruFlex® and Roundup Ready® canola varieties in the state.

Calling it a landmark event, Tim Murphy, Bayer’s Market Development Agronomist in South Australia said the introduction of this technology means growers have powerful new tools for management of in-crop weeds.

“There are a range of spray programs now available to South Australian canola growers when they choose to use Bayer’s Roundup Ready canola technologies by growing either TruFlex or Roundup Ready canola varieties,” he said.

“The Roundup Ready canola technologies allow for over-the-top applications of Roundup Ready PL Herbicide with PLANTSHIELD® technology, a liquid 540 g ai glyphosate, or Roundup Ready herbicide with PLANTSHIELD, a granule 690 g ai glyphosate for weed control in canola.”

Roundup Ready canola allows for the application of Roundup Ready herbicides from cotyledon to six-leaf, consisting of no more than two applications of a Roundup Ready herbicide in crop.

TruFlex canola allows for an extension of this window beyond the six-leaf growth stage, up to the first flower. With TruFlex canola varieties, growers have the choice of either a two-spray program or a three-spray program, depending on application rates or the weed pressure in the paddock.

With either program the best control is gained when the application of Roundup Ready PL is targeted at young, two to three leaf grasses and two to four leaf broadleaf weeds.

In 2021 Tim tested the flexibility and safety of Roundup Ready canola technologies in six canola systems trials in various locations around South Australia. A good example of how the technology performs was seen at Giles Corner in the state’s mid-north.

This trial included several spray programs that incorporated over-the-top Roundup Ready PL applications and/or the use of pre-emergent herbicides, as well as a traditional conventional spray program.

Planted on 28 April 2021, the trial had a hard start with minimal moisture at the time of seeding and it was nearly three weeks before enough rainfall was received to allow for germination. From that point on there was sufficient rainfall for both canola seed and weed seeds to germinate.

“The Giles Corner trial demonstrated the need to adopt an Integrated Weed Management (IWM) system when using Roundup Ready canola technologies,” Tim said.

Tim explained that there are several considerations for growers when developing an IWM program.

“Firstly, include a pre-emergent at sowing, which could be either propyzamide or newer herbicides like Overwatch®,” he said.

“Even with the dry start to the 2021 season at Giles Corner, the pre-emergent herbicide provided a good level of control.

“Also, target Roundup Ready PL applications at small weeds as the best control is gained when weeds are sprayed early.”

The trial also showed that the addition of clethodim in the tank at the two to four leaf spray helps reduce the potential for metabolic resistance developing to either clethodim or Roundup Ready PL herbicide.

“In most of Australia, we’re starting to see some strains of ryegrass that are showing a metabolic resistance to both clethodim and Roundup Ready PL, and we want to try and stop that becoming more of an issue,” Tim said.

“Work by Plant Science Consulting has shown that when you spray either of those two actives on their own, the plant can recover and grow on from it, but when you mix them in a tank and spray it over the top of a crop, we’re getting nearly complete control.

“So, we’re stopping that resistance spread of either metabolic resistance from the glyphosate, or metabolic resistance from the clethodim.”

The overarching piece of advice Tim had for developing a solid IWM program is to mix and rotate products to maximise the longevity of all herbicides in the industry.

“Just because TruFlex canola and Roundup Ready canola, provides the ability to use a two-spray or a three-spray program, I’d still question whether a spray is always necessary,” Tim said.

“I recommend monitoring crops and tailoring applications based on the weed spectrum.”

The point about crop competition is an important one, with the vigour of hybrid varieties playing a key weed management role in canola growing systems.

“Results from these trials indicate that the increased vigour from hybrid varieties, including those with the TruFlex or Roundup Ready traits, provide the potential for improved yields and crop vigour over the conventional varieties,” Tim said.

“In summing up, these trials have demonstrated Bayer’s Roundup Ready canola technologies are tolerant to over-the-top applications of Roundup Ready PL, providing excellent in-crop weed control and crop safety, helping to maximise yield potential.”

Article written by Bayer for Seasons magazine. 

TruFlex® and Roundup Ready® are Registered Trademarks of the Bayer Group.
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