Top Crop Manager

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Glyphosate use in canola production systems

Growers still have concerns about glyphosate resistance management

November 20, 2007  By Top Crop Manager

Despite research showing a low incidence of glyphosate resistant weeds in North
America and no confirmed cases of glyphosate resistant weeds in western Canada,
growers still have concerns about glyphosate resistance management and how the
use of glyphosate in canola should be managed on their farms.

According to Rob Neyedley, technology manager, Monsanto Canada, Roundup brand
herbicides and Roundup Ready canola are used as part of a diverse cropping rotation
in western Canada. When Roundup Ready canola is grown in rotation with cereals,
pulses and other oilseed crops, herbicides with alternate modes of action are
used (see Figure 3).

"It is these typical crop rotations used in western Canada that help minimize
the probability of glyphosate resistant weeds developing," says Neyedley.


Group 1 product examples – ACCase
Centurion, Select, Fusion, Assure II, Poast, Horizon, Achieve, Puma, Venture.

Group 2 product examples – ALS
Refine, Express, Frontline, Muster, Odyssey, Pursuit.

Note: Glyphosate was used the same number of times in each rotation, though
at different times.

Research also shows that the contribution of glyphosate herbicide resistant
canola to overall glyphosate selection pressure is still relatively low. Less
than 15 percent of total area for all crops treated annually with herbicides
receives an in-crop glyphosate application. In comparison, Group 1 products
are applied to 42 percent of the total area for all crops treated annually with
herbicides and Group 2 products are applied to 38 percent of the total area
for all crops treated annually with herbicides.

And even though glyphosate can be applied at multiple times throughout the
year, these applications often target different weed species and populations,
which reduce overall selection pressure for glyphosate resistance. For example,
pre-harvest and post-harvest applications primarily target perennial weeds in
the fall. Due to the biology of perennial weeds, occurrence of herbicide resistance
is low. Pre-seed applications, which target annual weeds in the spring, are
typically followed by crop competition and an alternate in-crop herbicide application
which further reduce the selection pressure for glyphosate resistance. Glyphosate,
although able to be used throughout the year, is used on different weed populations
based on the time of application.

Neyedley is the first to concede weed resistance to any herbicide should be
taken seriously, but he does not want growers to over-react and make poor choices,
suggesting growers should not shy away from growing Roundup Ready crops or using
Roundup brand herbicides for fear of developing glyphosate resistance.

"In fact, Roundup brand herbicides and Roundup Ready canola have actually
helped manage weeds that are resistant to other herbicide groups for over 10
years now in Canada."

Recommendations to limit the
likelihood of glyphosate resistance*

Agronomic recommendations

  • Always read and follow label directions. Always apply glyphosate at the
    full-labelled rates for effective weed control. Weed escapes are more likely
    to occur when glyphosate is applied below labelled rates.
  • Always apply at the correct weed staging. Rate guidelines have been developed
    for specific weed stages and to be effective, the rates used need to match
    the weed's growth stage. Most weeds are easier to control when small.
  • Studies show that using the right herbicide product at the right rate at
    the right stage of weed development is the most critical action to minimize
    the risk of weed resistance.
  • Add other herbicides and cultural practices where appropriate as part of
    the Roundup Ready cropping system.
  • Always consult the current approved label for specific recommendations and

Glyphosate stewardship in general

  • Monsanto takes product stewardship and claims of resistance to glyphosate
    very seriously.
  • Monsanto continually evaluates its recommendations for weed control efficacy.
  • Monsanto is committed to working with growers to address weed resistance
    to glyphosate. We encourage growers to report suspected cases of resistance
    to Monsanto so the company can investigate and address potential resistance
    and implement recommended control measures if resistance is confirmed.
  • The effective and profitable use of Roundup and Roundup Ready crops has
    continued in areas where glyphosate resistance has occurred. Glyphosate resistant
    weeds have been effectively managed by using tank-mixes and/or cultural weed
    control methods.

*Taken from Monsanto's agronomic and stewardship recommendations.
Report any incident of non-performance to your local retailer or Monsanto Representative
or CustomCare at 1-800-667-4944.



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