What Can I Use to Kill Canada Thistle?
Canada thistles are creeping perennial weeds that have extensive root systems. These weeds are difficult to kill, because any part of the root system that remains in the soil can produce another plant. Therefore, digging the plant up and leaving parts of the roots in the soil will not effectively kill the plant. Gardeners have optimal success when they combine cultural and chemical control methods against Canada thistle, according to Colorado State University. Does this Spark an idea?
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Post-Emergent Herbicide
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Gardeners typically see Canada thistle weeds invade their lawns in mid-July through August, according to North Dakota State University. To kill off these invading weeds, use post-emergent herbicides. Use a post-emergent herbicide that contains an active ingredient such as MCPP, 2,4-D, dicamba, MCPA, triclopyr, carfentrazone or quinclorac, as suggested by the University of Illinois. Wait until the fall to apply a post-emergent herbicide to achieve optimal results. You also may apply a post-emergent spray between Canada thistle's bud and flowering stages.
Broad-Spectrum Herbicide
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Broad-spectrum herbicides that contain glyphosate are used to control Canada thistle. Glyphosate impedes Canada thistle's ability to produce proteins. Within a few days of spraying the herbicide, Canada thistles die off. Be careful when applying glyphosate to your lawn. This broad-spectrum herbicide kills off any vegetation that comes in contact with the spray. It's helpful to spray the Canada thistle and overseed the lawn a week after the herbicide application to prevent other weeds from growing in the weed's location.
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Landscape Fabric
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Landscape fabric may be used to smother Canada thistle weeds. The fabric works by generating enough heat to not only kill plants, but also seeds. To use landscape fabric, cut the material to fit over your Canada thistle growing location. Secure the edges of the fabric using landscaping pins. Increase the amount of heat generated underneath the fabric by spreading a 3- to 4-inch layer of mulch over the fabric. Use landscape fabric during the hottest part of the summer for optimal results.
Lawn Mower
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Reduce Canada thistle's vigor and energy by mowing. By removing the top portion of the plant, you'll force the root system to exert more energy into top growth. Eventually, the Canada thistle has spent all of its energy and dies out. Mow your Canada thistle plants before they have a chance to spread their seeds over the yard, or in early spring. Continue mowing throughout the growing season to prevent the plant from growing back.
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