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Control Canada ThistleHow to Get Rid of Canada Thistle

Canada thistle is a common invasive plant found in a wide range of areas, especially in the upper mid-west of the United States like in Indiana and Wisconsin. Canada thistle is a creeping perennial and so often it is seen in large patches that are spread colonially as this plant progresses in its dominance. It’s typically seen in a wide range of areas although it tends to do better in wetter areas.

How to Identify Canada Thistle

It’s important to differentiate Canada thistle with many of the biennial thistles that are common as its management techniques to treat them are quite different. The creeping perennial roots is one key way to identify it and another way to look at it is its distinct weeds which are usually not hairy at all. The lobes can be quite irregular from leaf to leaf.

Another key characteristic is the stem as there are not spines on the stem. The flowers that the canada thistle weed has are also unique as  the plant has dioecious plants which means they have male and female flowers which are very small compared to other thistles. As they mature, they produce this small light fluffy seeds which can blow off and disperse as much of the seed tends to just drop right where the parent plant is.

Canada thistle also has rhizomes down below ground and they tend to shoot up with new chutes, making for quite a sizable root system. This is what makes the Canada thistle especially difficult control because you have to not only control the growing points in the plant that you see above ground, you have growing points to kill below ground and then maybe even the growing points for the chutes that have sprung up above ground at least ten feet away. That being said, it takes a tremendous herbicide to be able to treat this kind of invasive, out-of-control species.

The Best Herbicides to Control Canada Thistle

2 4-D Amine Selective Weed Killer

RoundUp Pro Weed Killer

RoundUp Pro Weed Killer

Since Canada thistle has such an extensive root system and is so persistent, the best way to kill them is with Roundup or 2 4-D Amine Selective Weed Killer. These herbicides will kill back the leaves on the plant and will kill back part of that massive root system. The best time to apply these weed killers is on sunny days when the temperatures are between 65 and 85 degrees F. (18-29 C.).

When using Roundup, due to it being non-selective they will kill anything they touch, so it is best not to use these on windy days. If the Canada thistle you want to treat is located close to wanted plants, you might be better off to use a paintbrush to paint the herbicide on the Canada thistle just to be on the safe side.

Ideal Conditions For Using Herbicides on Canada Thistle

For best results and to ensure herbicides move foliarly downward through the plant make sure of these conditions:

  1. Adequate soil moisture from the soil surface well into the subsoil.

  2. Green leaves, not wilted and generally free from extensive damage caused by insects, disease, drought, hard freeze, dormancy etc.

  3. Shoot height is at least 10 inches tall in the early June and 8 inches or more inthe fall.

  4. Flowers not fully opened.

  5. The thistle has not been disturbed recently (within 2 months) by tillage.

  6. No mowing or cultivation should be done for 10 days after application.

Lastly, you may need to do repeated applications until you no longer see any more canada thistle. Check back weekly and spot treat as necessary.

For more information on controlling Canada thistle on your lawn and to get personalized advice and a plan of action from experts, contact us at
askapro@solutionsstores.com or call our customer service line at (800) 479-6583.

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