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Managing Weed Resistance

Perspective On Glyphosate Resistance

Source: Dr. Ian Heap www.weedscience.org
The graph compares the number of resistant biotypes by herbicide group over time. Glyphosate (Glycines) has among the lowest occurrence of weed resistance globally.

• It is difficult to predict when or where weed resistance might occur.
• No weed species in Canada have demonstrated resistance to glyphosate to date. Only 9 weed species in the U.S. (of the 14 globally) have shown resistance to glyphosate after over 30 years of commercial use.
• Where glyphosate resistance has occurred, it has been effectively managed by:
  • use of tank mixes
  • use of residual herbicides
  • tillage
  • mowing
  • good agronomic practices such as crop rotation, herbicide rotation
• When compared to other chemistries such as triazines (atrazine), and ALS inhibitors (Pursuit^®, Classic^®, Pinacle^®, Accent^®, etc.), incidence of resistance to glyphosate (glycines) is low.
• Glyphosate provides an effective alternative to some other herbicides, which have a higher risk of resistance development such as group 1 and 2.

Roundup^® Agricultural Herbicides Have:

• No residual soil activity.
• An active ingredient with a unique mode of action, which reduces the chances of weeds becoming resistant to glyphosate compared to other chemistry classes.
• Proven performance from years of on-farm use.

Dead Weeds Don’t Produce Seeds!

• Use the right rate at the right time.
• Always apply glyphosate at the full-labeled rates – this is essential for effective weed control. Weed escapes are more likely to occur when glyphosate is applied below labeled rates.
• Always apply at the correct weed staging. Rates have been developed in conjunction with weed growth, and are most effective when applied at the proper growth stage. Most weeds are easier to control when small.
• Optimizing weed control means reducing weed seed production and hence weed seed populations. This may lower subsequent weed populations and reduce the potential for development of weed resistance.

Optimize Agronomic And Economic Value

• Roundup agricultural herbicides can be used to unique advantage in combination with Roundup Ready seed technologies.
• Growers recognize and value the economic advantages of Roundup Ready Cropping Systems for unsurpassed weed control, crop safety and optimum yield potential compared to conventional systems.¹
• Grower adoption and use of Roundup Ready Cropping Systems show that growers recognize the need to balance the economic benefits of a production system vs the potential risk of developing a weed resistance problem, which may or may not occur on their farm.¹

Stewardship Recommendations

In order to optimize weed control, follow these weed management steps:

1. Use good agronomic practices and base your weed control programs upon local agronomic needs to provide optimum weed control.
2. Always start clean with a weed-free field – in reduced tillage systems, early emerging weeds should be controlled with an early burndown treatment – don’t allow weeds to get large because control will become more difficult and escapes more likely – this may lead to higher risk of developing resistance.
3. Use the Right Rate at the Right Time - Always use full, labeled rates for best control. The use rate should target the hardest-to-control species in the field. - Apply Roundup agricultural herbicides when weeds are at labeled stages. Annual and winter annual weeds should be small for best results.
4. If initial application is delayed and weeds are larger, a higher rate may be required.
5. Add other herbicides and cultural practices where appropriate as part of the Roundup Ready Cropping System.
6. Scout fields for possible escapes and take appropriate actions for effective control.
7. Report any incident of non-performance to your local retailer or Monsanto Representative or CustomCare^® at 1-800-667-4944.
8. Monsanto continues to support research in the use of Roundup Ready crops in Canada and the US. Research results to date indicate that the use of Roundup Ready technologies, either singly or sequentially, in typical Canadian agronomic rotations, presents low risk of development of glyphosate resistant weeds.

Always consult the current approved label for specific recommendations and details.

Remember...

• Glyphosate has a unique mode of action.
• It is difficult to predict when or where weed resistance might occur.
• Where glyphosate resistance has occurred, it has been effectively managed.
• Monsanto weed control recommendations are based on experience, continuing field research and collaboration with local experts.