Controlling Eastern Canada's Top 5 Weeds

Weeds affect your crop production by reducing yields – and, ultimately, profits – as they compete with your crops for resources, such as light, nutrients and moisture. Know the weeds in your fields and keep track of populations to stay on top of weed control and ahead of herbicide‑resistant weed development on your farm. To maintain glyphosate’s low risk status for developing resistance, and to prevent other herbicide resistances on your farm, use an effective tank-mix partner with glyphosate for weed control.




Lamb’s quarter is a fast-growing, annual, broadleaf weed that can reduce crop yields. If weeds emerge with the crop at 1 plant/m2, corn yield loss can reach 12%, whereas at 5 plants/m2, corn yield loss can reach 35%. Soybean yield loss can reach 13% at 1 plant/m2 and 38% at 5 plants/m2.1


This weed is a prolific seed producer, and seeds can remain dormant in the soil for many years. Germination usually begins in mid- to late May and continues until August.


Control Tips

  • Scout for weeds early and often.
  • For soybeans and corn, take advantage of the pre-plant, pre-emergence and post-emergence herbicide options with residual activity.
  • Always use an effective tank-mix partner with glyphosate, and apply post-emergence herbicides early, as they are most effective on weeds during their initial growth stages. Control diminishes as plant size increases.




Green foxtail is a shallow-rooted, annual, grassy weed. Green foxtail reproduces by seed, which can remain viable in soil for approximately three years. Germination usually takes place late May or early June and can continue until September. Warm spring temperatures are favourable for foxtail’s growth. A weed population of 5 plants/m2 can reduce crop yields by up to 7% in corn and 8% in soybeans. 2


Control Tips

  • Scout fields frequently for this weed: under hot conditions green foxtail can grow quickly and escape the herbicide application window.
  • At approximately 34,000 seeds per plant, it’s a heavy seed producer; however, it’s a poor competitor. Healthy crop stand establishment will help your crop outcompete this weed.
  • Start clean with a pre-plant burndown, and include a tank-mix partner that provides residual control of green foxtail and other grassy weeds.



Dandelion is a perennial, broadleaf weed, found in almost any habitat. Dandelion flowers from early spring to late autumn.


Control Tips


In corn and soybean crops, pre-plant herbicide applications are effective at controlling established weeds and newly-emerged seedlings. Fall glyphosate applications are excellent for controlling larger, more established dandelions. The active ingredient in systemic herbicides moves to the roots at this time of the year, providing long‑term weed control.





Canada fleabane is an annual, or winter annual, broadleaf weed. The number of seeds produced per plant is proportional to its height. Forexample, a 0.4-metre tall plant produces around 2,000 seeds, whereas a
1.5-metre tall plant produces approximately 230,000 seeds.3

​Fleabane’s seeds can survive in soil for up to three years. Seedlings often emerge from late August to October and overwinter, while others emerge from March to early May. Like many other weed species, yield losses are proportional to time of emergence and weed density.

Control Tips

  • Scouting is essential to weed control.
  • In conventionally-tilled systems, tillage provides weed control in corn and soybean crops.
  • In no-till systems, a pre-plant burndown of glyphosate and an effective tank-mix partner is required.


Canada fleabane juvenile


Recommendations for Control of Glyphosate-Resistant Canada Fleabane

Genuity Roundup Ready 2 Yield® Soybeans Roundup Ready 2 Xtend® Soybeans ​Winter Wheat Corn Hybrids with Roundup Ready® 2 Technology


(Tank mix with Roundup Transorb® HC)

Integrity®, Optill® or Eragon® + Sencor®.

XtendiMax™ with VaporGrip™
Technology + Eragon, Integrity or Optill.
​-- Dicamba, Integrity, Marskman®, or Callisto® + atrazine. 


(Tank mixed with Roundup WeatherMAX®)

-- XtendiMax with VaporGrip
Technology as needed.
Infinity® Dicamba, Distinct®, Marksman,
or Pardner® + atrazine.



Field horsetail is a perennial weed and strong competitor with many crops. This weed reproduces by spores and rhizomes (horizontal underground stems). In early spring, spore-producing cones top leafless
shoots. These cones shed their spores in early May. From late spring onwards, the ash-grey stems die back and second shoots emerge from the ground. These shoots develop whorls of six to eight green, leafless branches. Field horsetail never produces flowers or seed.


Control Tips

  • Herbicides usually only provide top growth control because of the difficulty of placing the active ingredient near rhizomes and tubers. However, repetitive attacks on the above-ground plant with herbicides, shading, mowing and hand weeding may deplete the weed’s reserves to the point that the plant dies.
  • Remove new stands before they spread, and clean equipment between fields.
  • Glyphosate does not provide long-term control of field horsetail.


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1 “Lamb’s-quarters, Chenopodium album.” Agriculture and Agri-Food Canada, n.d. Web. 7 Apr. 2016.
2 “Green foxtail, Setaria viridis.” Agriculture and Agri-Food Canada, n.d. Web. 7 Apr. 2016.
3 “Canada Fleabane Factsheet.” Ontario Ministry of Agriculture, Food and Rural Affairs. Online.