Origin:
Native to Europe, but found throughout the United States and Canada, and listed as a “Noxious Weed” in several states.
Biology:
A biennial weed that forms a large basal rosette of leaves the first year of growth, and a tall, well branched stem in the second year. Reproduction is from seeds, and the seed pod is a large, spiny bur that persists on the plant into the winter. Plants can be very large and form thick stands, and this is a serious pest in landscape and agriculture, as well as along roadside and in other disturbed areas.
Identification:
Mature plants can grow to over 5 feet in height, and with the many branches spreads to 4 or 5 feet in diameter as well. The thick stems are hollow and covered with hairs. The leaves are very large, up to almost 2 feet in length, and are alternate and generally egg-shaped to elongated oval. Their margins are deeply wavy or scalloped, and the lower surface is covered with short, soft hairs. The flower heads are very thistle-like in appearance, with the purple disc flowers on top of the large, round ball of spiny bracts, the spines ending with a short hook. This plant is separated from true thistles by the large leaves and the hooked bracts.
Characteristicts Important to Control:
Physical removal is effective, but plants have a large, thick taproot that may extend up to a foot deep in the soil. A contact or systemic herbicide will effectively control the plants, and seeds may be prevented from germinating with a pre-emergent product.
