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Research on emerging weed management issues in corn, soybean and cereals

Principal Investigator: Peter Sikkema

Research Institution: University of Guelph (U of G)

Timeline: April 2019 – March 2024  


  • Determine annual rye grass control in corn with glyphosate plus Group 2 herbicides.
  • Determine the effect of time-of-day and adjuvants on the efficacy of Shieldex for weed management in corn.
  • Does the addition of Roundup Weathermax accentuate corn injury with Shieldex?
  • Determine the effect of delayed postemergence herbicide application on yield loss in corn.
  • Determine the benefits of applying a fungicide following broadleaf herbicides applied POST in identity-preserved (IP) soybean.
  • Ascertain if tankmixes of Roundup plus Pinnacle accentuate soybean injury and yield loss.
  • Determine the effect of delayed postemergence herbicide application on yield loss in soybean.
  • Determine control of common chickweed in winter wheat.
  • Determine annual rye grass control in corn with glyphosate plus residual herbicides.
  • Control of suspected Group 4-resistant green pigweed in corn. 
  • Tolerance of corn to Terrad’or applied preplant.
  • Control of suspected Group 4-resistant green pigweed in soybean.
  • Control of putative Group 1-resistant large crabgrass in IP soybean.
  • Tolerance of soybean to Terrad’or applied preplant.
  • Tolerance of soybean to Warrant applied PRE, ePOST and mPOST.
  • Develop weed management strategies in strip-till corn.
  • Determine the efficacy of various approaches to weed management in IP soybean.
  • Determine the benefits of fall weed control in winter wheat.
  • Control of putative Group 14-resistant common ragweed in IP soybean.


  • Identification of the most efficacious strategies for the control of Group 4-resistant green pigweed in corn and soybean, Group 1-resistant large crabgrass in IP soybean, and common chickweed in winter wheat will help farmers select effective herbicides that target the weed problem, resulting in improved crop yield and increased profitability while avoiding unnecessary application of pesticides in the environment.
  • Information on the impact of delayed postemergence herbicide application on yield in corn and soybean will help growers implement weed management strategies that minimize crop yield loss and increase yield and net returns.
  • Development of weed management programs in strip-till corn will support new crop production systems that will help reduce wind and water erosion while also improving soil structure and soil health.
  • Development of weed management practices incorporating new herbicides such as Shieldex, Terrad’or and Warrant and new herbicide resistant technologies (E3, HT3, and HPPD-resistant soybean) will help Ontario growers understand the best biological fit for these new weed management tools.

Scientific Summary:

Ontario corn, soybean and cereal farmers continue to face new and unpredictable weed management issues that need to be addressed with local research. Weeds that were previously being effectively managed are now posing a substantial challenge to producers in Ontario. Some notable examples of this trend include poor control of green pigweed with Group 4 herbicides in Kent County, poor control of crabgrass on a farm in Huron county with Group 1 herbicides in IP soybean and poor control of common ragweed in IP soybean in Lambton county with Group 14 herbicides. Confirmation of these putative resistant biotypes is needed along with the development of solutions to control these putative resistant weeds which, left unchecked, will have a negative effect on crop yield and net returns for affected Ontario farmers (e.g., preliminary research shows corn yield losses of 5 bu/ac for every inch in weed height).

While there have been studies completed on the impact of delayed postemergence herbicide application in corn and soybean, these studies are now out-of-date. With new, high yielding corn hybrids and soybean cultivars these previous studies are no longer relevant. As a result, Ontario corn and soybean producers need up-to date information in order to implement weed management programs based on current data to allow them to maximize their net returns.

New weed control studies are also needed to reflect the increased interest in (and the greater number of acres of) strip-till corn in Ontario. It is anticipated the weed species composition and density will be different in the tilled compared to the non-tilled portion of the field. Consequently, weed management programs will have to be adjusted. 

As a result, this research aims to provide Ontario growers with new knowledge enabling them to address the weed management issues identified above in order to maintain their farm profitability for corn, soybean and cereal production.

External Funding Partners: