Close up of canada thistle weed

Canada Thistles

Controlling thistles in corn

Close up of Canada Thistle 

Canada thistle patch in field 

young canada thistle weed

Thistles are sometimes called “emotional weeds”. It’s not because they feel anything, but because they can spark some strong reactions when spotted in a field.

Classified as noxious weeds in Ontario,1 Canada thistle and sow thistle are incredibly strong competitors for moisture, nutrients and light. Even small populations can reduce crop yields significantly – Manitoba Agriculture reports one study showing that a mere 14 Canada thistle shoots per square metre can reduce wheat yields by 38%.2

Why are they so difficult to get rid of? Mostly because they’re built for survival.

  • Perennial sow thistles have complex, creeping root systems that can grow two to three metres deep, on average, and spread horizontally as far as six metres in a single season.3
  • Canada thistle perennial propagate two ways, which complicates control efforts.
    • Underground rhizomes and roots: New plants germinate directly from the roots or rhizomes, which is the main mode of propagation.
    • Seed: Canada thistle’s distinctive purple flowers and perennial sow thistle’s dandelion-like yellow flowers both produce fluffy seed heads that disperse seed on the wind.
  • Thistles survive winter by driving nutrients and energy deep down into their root or rhizome systems. Cultivation to break up roots only encourages new growth as new shoots can germinate from root or rhizome fragments.

Corteva Solutions

Controlling thistles in corn – indeed in any crop – requires a multi-year approach and a strong focus on an integrated pest management plan that uses multiple modes-of-action to slow resistance, particularly if you’re growing glyphosate-tolerant corn. 

An effective control plan starts with managing thistle top growth to lessen crop competition and prevent seed production. Using herbicides with systemic activity can also help to diminish the plants’ undergound energy stores over time.

Lontrel XC logo

Lontrel XC herbicide from Corteva is a Group 4 systemic product that translocates throughout the plant for more effective, long-lasting thistle control.

  • Higher concentration XC formulation means you can cover more acres with one jug.
  • Lontrel XC alone can be safely applied to all field corn, including herbicidetolerant types, from spike to V6 (8-leaf).*
  • Tank mix Lontrel XC with glyphosate for enhanced control of Canada thistle and perennial sow thistle.**

To sum up

Thistles are tenacious survivors and difficult to control for a number of biological reasons. A multi-year, multi-crop, multi-herbicide approach can help weaken the extensive underground root system and energy storage, but annual efforts to control top growth is key to protecting corn yields.

*Do not apply Lontrel XC to sweet, seed or popcorn.
**Tank mix designed only for glyphosate-tolerant corn hybrids.

1Ontario Ministry of Agriculture, Food and Rural Affairs. Noxious weeds in Ontario.

2Manitoba Agriculture, Canada thistle information page.

3Alberta Agriculture and Forestry. Canada thistle Pest Selector page.