Canadian Thistle
The Canadian thistle is a forb with a height of about two to five feet. It has horizontal and wide-spreading roots, and stems that are a bit hairy. It has tapering leaves that are oblong in shape and divided deeply, and margins that are prickly. It has many compact, small white or rose purple flowers that will arrive on the top stems from June through September. Its seeds are fairly small, smooth and light brown in color, and each has a tan hair tuft that is attached to the tip, loosely.
This thistle is different from other types of thistle because it has smaller flower heads, thinner stems and more deep-running roots. If you want to eradicate it in a field or lawn, consult your local extension office, or look the plant up on the internet, to make sure you're getting rid of the right weed.
Canadian thistle originally came from Europe. It can be found in areas around the northern United States, and is mainly seen in areas that are east of the Rocky Mountains. It grows well in old pastures and old neglected fields, where the soil has been disturbed, but not attended to recently. You can sometimes find it in marshy areas where the water level is different from one season to the next. It can also grow in prairies and meadows. If your pastures are established and predominantly weed-free, thistle will normally not invade them. The plants are tall with just a few flowers, and they prefer areas that stay shady most of the day.
Canadian thistle can crowd out and replace native forbs and grasses. It has a negative effect on areas where it pushes in, such as the edges of housing communities, where the earth has been disturbed and not planted with grass or other plants.
If you try to get rid of thistle on your land, use fire only in the late spring; otherwise, the fire can cause more sprouts. You can burn an area of thistle to remove it, but only if you do it in May and June. If you till the area, be sure to plant something hardy in the tilled area, or you will have created the perfect area for a reinfestation. Grazing doesn't normally work to rid a field of thistle, because it has prickles that will prevent the livestock from eating it.
To manage an agricultural area and keep Canadian thistle out, you should develop fields of plants that are hardy and natural to the area. This may prevent infestation. If you hand-cut or pull thistle, this will starve the stems underground, eventually. You will need to cut or pull them at least three times each growing season. If you have a heavier infestation, pulling by hand will probably take too much time, and you will be better off applying the herbicide 2,4-D.