Glyphosate Resistance in Manitoba

Are there really glyphosate resistant weeds here in Manitoba? According to research conducted by Stratus Agri-Marketing in an on-line survey, the 281 Manitoba farmers that responded believe there are more than 43,000 acres infested with glyphosate resistant weeds, an estimated 23,000 with resistant kochia.

These occurrences have not been scientifically proven but they very well may be actual cases of resistant weeds. Results of a herbicide resistance screening survey done by Manitoba Agriculture this fall are expected early this year and it is expected that there will be evidence of resistance found since both Saskatchewan and North Dakota have confirmed incidences of resistant weeds.

According to the Manitoba Agriculture website, herbicide resistance in kochia develops on fields where there is repeated use of Group 2 herbicides over several seasons. The best way of delaying resistance development is to rotate the use of broadleaf herbicides, using different Groups of herbicides as part of a long-term weed management strategy.

Instituting changes in weed management practices is the key in improving the overall level of weed control but the bottom line is reducing the intensity of glyphosate use to lower the potential for resistance. Manitoba Agriculture suggests using different agronomic practices to manage weeds so the reliance on any one type of weed control technique is reduced. Weeds are less able to adapt to a constantly changing system that uses many different control practices.

Some of the management practices suggested for lessening the potential for developing glyphosate resistant weeds are:

  • Rotate between Roundup Ready and conventional crops;
  • Rotate glyphosate with herbicides that have different modes of action;
  • Use different application windows during the year, pre-seeding, in-crop, pre-harvest, or post-harvest;
  • Place the fertilizer where the crop has access to it;
  • High seeding rates can give the crop the edge;
  • Narrow row spacing allows the crop to be more competitive;
  • Shallow seeding for fast crop emergence;
  • Use high quality seed for vigorous seedlings;
  • Annual weeds will grow where annual crops are frequently grown, so vary the life cycle of the crops grown;
  • Crop rotation is the foundation to keeping the weeds off balance.

Repeated use of the same chemicals and practices every year is the factor that contributes to the adaptability or resistance of weeds. A constantly changing system using different practices in rotation has a greater chance of preventing and/or minimizing the occurrence of the difficult to control weeds.