Glyphosate resistance on the rise

Grain Central, October 1, 2019

NEW research from Bayer has revealed 85 per cent of cotton growers surveyed in 2019 suspect they have glyphosate-resistant weeds on farm, an increase of over 10 per cent since 2016.

Despite increasing levels of resistance, glyphosate continues to perform well in the Roundup Ready Flex system, with 93 per cent of growers rating the level of weed control achieved as ‘excellent’ or ‘good’.

Bayer says glyphosate is a critical herbicide for the cotton industry, and for agriculture in general, so protecting the longevity of the product is important.

Concern over herbicide resistance has prompted Bayer to initiate a program to help the cotton industry better understand glyphosate usage and integrated weed management (IWM).

“Over the last 20 years, over-reliance on glyphosate has seen a marked decrease in residual chemistry use within cotton systems and has also been a key contributor to the development of glyphosate resistance,” Bayer brand manager Kate Connors said.

“In 2016, insights gathered from 200 farmers and consultants led to the development of several initiatives to assist cotton growers in implementing their on-farm IWM program.

“Bayer now offers free herbicide resistance testing, the Roundup Ready PLUS program, which rewards cotton growers who use herbicides sustainably, and the Mix It Up website, to help growers manage herbicide resistance.”

Bayer conducted further research in 2019 to understand any changes in prevalence of glyphosate resistant weeds and IWM practices.

Key findings from the 2019 research program:

1. Glyphosate resistance is increasing

In 2019, 85 per cent of growers surveyed suspect they have glyphosate resistant weeds on-farm, up from 74pc in 2016. In each valley surveyed, the number of growers with glyphosate resistant weeds on farm has increased from the 2016 base.

2. Fleabane, Feathertop Rhodes Grass and Annual Ryegrass are the biggest weed challenges

3. Non-glyphosate herbicide resistance is increasing

Group J and K herbicides featured in the survey for the first time, showing growers’ increasing concern, particularly in controlling Fleabane, Annual Ryegrass (Group J) and Feathertop Rhodes Grass (Group K).

4. Glyphosate continues to perform well in the Roundup Ready Flex system

93pc of growers rated the level of weed control achieved as Excellent or Good.

5. Growers use an average of 4.9 applications of glyphosate per cotton season

This equates to an average of:

  • 9 applications during fallow (compared to 2.1 in 2016)
  • 6 applications at sowing (compared to 0.5 in 2016); and
  • 4 applications over-the-top of cotton (compared to 2.7 in 2016)
  • Pre-emergent herbicide use is increasing

Since 2016, pre-emergent herbicide use has increased by 13pc. This increase may be due to several factors, including Bayer’s Roundup Ready PLUS program, with an increase in the use of program herbicides.

6. Cultural practices are being used to control surviving weeds

Growers are implementing cultural practices in-crop to manage surviving weeds. 84pc of growers took action to control surviving weeds, the majority through inter-row cultivation (51pc) and chipping (32pc).

Source: Bayer. Visit for further details. 





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