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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.


Step One: Identification It's important to identify the type of weed you have to make sure that it is actually canada thistle and not some other similar looking invasive weed. Knowing the exact weed you are encountering on your lawn will help you to understand what the weeds tendencies and characteristics are and also which one of our products can best treat that particular weed. This is important because some more stubborn weeds have a high tolerance or resistence to particular herbicides and control methods and are specifically labeled for certain weeds and not for others. If you misdiagnose the weed on your lawn as canada thistle when it's in fact not, you may purchase a herbicide not meant to tackle it and it will lead to disappointing results and overall, a waste of money. We don't want that.  If you are unsure of what weed you have, you can contact us at identification@solutionsstores.com and send us a photo of your weed and we will identify it for you and suggest treatment options.


Step Two: Inspection. Once the plant has been properly Identified, you can then move to the inspection process. Chances are, if you have canada thistle, they are not hard to miss and they stick out like a sore thumb on your lawn amongst your desired grass and vegetation.Canda thistle is a creeping invasive perennial weed that be very difficult to control. Canada thistle not only produces seed much like a dandelion seed head but it also has an extensive root system that goes deep into the ground and can repeatedly return even from a small piece or root left behind. Canada Thistle is a lighter colored green, deeply lobed, leaves which are prickly looking and resemble spears. If they grow enough to flower, the flower is a purple pom-pom shape that will be produced in small clusters at the top of the plant.

Step Three: Control. Canada thistle can be killed with either RoundUp Pro Weed Killer or 2 4-D Amine Selective Weed Killer. These professional quality herbicides will deal damage to the leaves on the plant and mess with the development of the root system. The best time to apply these herbicides are on warmer days when the temperatures are between 65 and 85 degrees F. Because these weed killers are non-selective, any plant that comes in contact with the chemical will be killed, so it would be wide to apply on days where it is not windy . If you need to treat Canada thistle where it is close to your desired plants and grasses, you might be better off using a paintbrush to paint the weed killer on the Canada thistle. Reapplication may be necessary to completely eliminate the plant because canada thistle is very stubborn and persistent.


Step Four: Prevention. The best defense against ground ivy is a thick lawn that is well fertilized and maintained. Implement proper cultural practices such as watering, mowing and feeding to make your yard less conducive to canada thistle making a return and invading your yard.

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Learn More About Canada Thistle

Canada thistle isn't just a problem on home lawns it is also a detriment to farmers and growers in the agricultural industry, especially in Canada as its name implies. Canada thistle can cause greater crop losses than any other perennial broadleaf weed in various regions and it continues to spread. It's the number pernnial broadleaf weeds farmers target.


The success of Canada thistle results from the hardiness of the plant. It's persistent root system and its powerful ability to reproduce. Within 19 days of emergence, at the two leaf stage, seedlings can regenerate after top growth removal. By the three leaf stage, the plant has already developed an extensive root system with numerous buds. Thick fleshy roots grow deep into the soil in search of consistent moisture.


Canada thistle roots being six to ten feet deep is not uncommon and they can grow as deep as 18 feet. Lateral roots extend up to twenty feet in diameter from the plant. The lateral root system produces multiple nodes which helps Canada thistle spread throughout a field or landscape. Breaking up the root system with mowing or tillage can only add to the problem. Root fragmants can survive 100 days in the soil and new thistle plants will sprout from pieces as small as 3/8 of an inch in length.


Canada thistle reproduces mainly by roots but can also reproduce by seed. Merely one canada thistle plant can produce up to 5,000 seeds which can germinate 10 days after reaching maturity. Seeds remain viable for up to six years and when buried may lay dormant in the soil for up to 20 years. Even light infestations of Canada thistle can cause significant yield loss in cereals and canola with losses as a high as 70% have been reported.


Most herbicides suporess Canada thistle top growth only but because of the persistent root system, suppressing the top growth is like giving the thistle a haircut. The only effective long-term control strategy is a herbicide that translocates deep into the roots. A single treatment with a root targeting product can get rid of thistle in the year of application and can reduce the possibility of Canada thistle returning by 73% the following year.


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The Best Herbicides to Control Canada Thistle

Since Canada thistle has such an extensive root system and is so persistent, the best way to kill them is with RoundUp Pro Weed Killer 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.

Better Safe Than Sorry: Equip Yourself With Protective Safety Equipment Before Spraying

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 in the 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.


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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.


Additional Resources:

Canada Thistle - 3.108 - ExtensionExtension


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