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Ontario Grain Farmer Magazine

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

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  

Objectives:

  • 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 tank mixes 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 putative Group 4-resistant green pigweed in corn. 
  • Tolerance of corn to Insight applied preplant.
  • Control of putative Group 4-resistant green pigweed in soybean.
  • Control of putative Group 1-resistant large crabgrass in IP soybean.
  • Tolerance of soybean to Insight applied preplant.
  • 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.

Impacts:

  • 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 and Insight and new herbicide-resistant technologies (E3, HT3, and HPPD-resistant soybean) will help Ontario growers understand the best biological fit for these new herbicide-resistant soybean seed offerings.

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 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 identity preserved (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.

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. 

This research aims to provide Ontario growers with new knowledge enabling them to address the weed management issues identified above to contribute to profitable production of corn, soybean, and cereals in Ontario.  

Results:

Waterhemp with a Serine264Glycine amino acid substitution has been confirmed in Ontario. This resistance mechanism confers resistance to both atrazine and metribuzin. This biotype is present in at least 3 Ontario counties.

Control of putative Group 4-resistant green pigweed with eleven Group 4 herbicides was <85%. Based on preliminary data, effective control strategies in corn and soybean, applied PRE or POST, have been identified. In corn, Engarde and Acuron, applied PRE provided good control of green pigweed, and Distinct, dicamba, alex, Marksman and atrazine, applied POST, provided good to excellent control. In soybean, Sencor, Bifecta, TriActor, and Fierce, applied PRE, provided excellent control of green pigweed, and Flexstar GT and Roundup provided good and excellent control of green pigweed in Roundup Ready soybean, respectively.

Control of Group 1-resistant large crabgrass was < 45% with Poast, Assure, Venture, Achieve, Puma Advance, and Simplicity. Very interestingly, Select, applied POST, controlled this large crabgrass biotype 81%.

The delayed postemergence herbicide application in corn in high weed density environments until weeds are 5 cm in height results in a yield loss of 5.0 bu/ac or $32/ac. When herbicide application is delayed until weeds are 10 cm in height there is a yield loss of 17.4 bu/ac or $111/ac.

The delayed postemergence herbicide application in soybean in high weed density environments until when weeds are 5 cm in height results in a yield loss of 1.8 bu/ac or $27/ac, when herbicide application is delayed until weeds are 10 cm in height there is a yield loss of 5.1 bu/ac or $75/ac.

The two-pass programs of Boundary, Authority Supreme, or TriActor applied PRE followed by Basagran + Reflex + Assure applied POST controlled annual broadleaf weeds 62-100% and annual grasses 94-99%, respectively. Weed interference reduced soybean yield 40% in this study. Reduced weed interference with the two-pass programs of Boundary, Authority Supreme, or TriActor applied PRE followed by Basagran + Reflex + Assure applied POST resulted in an increase in soybean yield of 16 -19 bu/ac.

Refine, Refine M, Barricade M, Luxxur, and Luxxur M, applied POST, provided excellent control of common chickweed in winter wheat.

GR Canada fleabane control with the fall compared to spring herbicide applications was 89 and 99%, respectively. The control with the sequential herbicide application of a fall application followed by a spring application was 100%. Although GR Canada fleabane control was better with the spring herbicide application, winter wheat yield was higher with the fall application due to reduced weed interference.  Across all herbicides evaluated, winter wheat yield with the fall compared to spring herbicide applications control was 58 and 51 bu/ac, respectively.

Recommendations:

Weed management in corn and soybean needs to be planned on a field-by-field basis. Farmers should plan to use a two-pass weed control program of an effective soil-applied herbicide followed by a postemergence herbicide.

The soil-applied herbicide should be selected based on:

  1. Weed species composition in each individual field,
  2. Soil characteristics including soil type, OM, CEC, and pH, and,
  3. Future crops in the rotation.

The use of postemergence only herbicide programs can result in substantial yield losses when herbicide application is delayed due to:

  1. Multiple rain events
  2. Windy conditions
  3. Large acreages
  4. Equipment breakdowns

Ontario farmers are encouraged to introduce more diversity into their weed management programs including cultural, mechanical, biological, and chemical weed control tactics. The over-reliance on chemical weed control to the exclusion of other weed control tactics has resulted, and will result, in the continued selection of herbicide-resistant weed biotypes.

External Funding Partners:

BASF

Bayer