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Tips for managing fall weeds in Ontario
Tips for managing fall weeds in Ontario

Tips for managing fall weeds in Ontario

OMAFRA lists three ways to utilize your window for herbicide application 


By Kaitlynn Anderson

Staff Reporter


In this week’s field crop report, OMAFRA offered a few tips for farmers to use their herbicide application window to the best of their advantage. 

First, farmers should “choose the most effective products, rate and tank mixes for the perennial weed that you are targeting,” according to the field crop team.

A team in the department of plant agriculture at the University of Guelph provided the following table in the report, which outlines the “best herbicide option for each targeted perennial plant”:


Perennial Plant


Product Rate

Average Control (Range in control)


Glyphosate (540 g/L)

1.34 L/ac

90% (84 - 100%)

Perennial sow-thistle

Glyphosate (540 g/L)

1 L/ac

90% (85 – 100%)

Canada thistle

Glyphosate (540 g/L)

1.34 L/ac

90% (85 – 100%)


Glyphosate (540 g/L)+ 2,4-D Ester (564 g/L)

0.67 L/ac + 0.5 L/ac

95% (90 – 100%)

Wild carrot

Glyphosate (540 g/L)

1.34 L/ac

82% (49 – 100%)


Glyphosate (540 g/L)

1.34 L/ac

90% (85 – 100%)

Red clover

Glyphosate (540 g/L)+ Distinct

0.67 L/ac + 200 g/ac

99% (96 - 100%)


Second, farmers may want to consider applying herbicides in the late morning or during the middle of the day, when air temperatures are above eight degrees Celsius for at least two hours following application. This ensures that the “targeted plant is taking up glyphosate during the heat of the day,” according to the OMAFRA team.

Third, the team recommends waiting two to three days after a frost event to evaluate weed growth.

“Depending on how cold (temperatures were), the plants may be damaged and no longer growing,” said Dale Cowan, a senior agronomist with AGRIS and Wanstead Cooperatives. “Plants need to be actively growing to take in herbicide.”

By waiting for the plants to resume growth before applying herbicide, the weeds will then be able to take up the product, he said.

If the plant that farmers are wishing to control looks fine, then they may want to consider resuming herbicide application once the temperatures have again risen above eight degrees Celsius.

The team also encourages producers to wait 72 hours to till the soil after a herbicide application.

“The longer that you can wait after application before making a tillage pass, the more the herbicide will translocate within the plant and do a more effective job controlling the species,” stated the report.


Learn more about weed management in the field guide.


Photo: La Corivo / iStock / Getty Images Plus