Johnson County Secondary Roads Tall Thistle Weed

Tall Thistle (Cirsium altissimum)

Description: Tall thistle, also known as field thistle and pasture thistle, is a biennial, reproducing by wind blown seed. The first year it is a rosette of leaves with long petioles, dark green on the upper side and wooly white on the underside. The roots of the rosette may enlarge and develop tubers. The leaves are moderately to coarsely lobed or may be spatulate shaped with almost even edges. The edges have short spines, the upper sides are sparsely hairy, and the undersides are very hairy. The second-year stems are erect, branched, green, and slightly hairy. The many leaves on the second-year plant are also quite variable in shape. Like those of the rosette, one plant may have leaves varying from nearly smooth edged to deeply lobed. The dark green, sparsely hairy upper side, in contrast to the whitish, wooly underside, help to identify this species. Flowers are produced on the tips of the branches. They are rose-purple, about 1 inch in diameter, with round buds and spiny bracts. Although the stem elongates in June and July, the plant does not bloom until August and September. Seeds mature in September and October.

Distribution: Tall thistle is found throughout Johnson County and Iowa. It grows in roadsides, waste places, abused pastures, and idle cropland.

What’s The Problem?: Tall thistle can rapidly infest disturbed areas, CRP ground or other areas through wind blown seed, and seed carried by birds and animals. The sharp, spiny leaves and flowers are painful to contact and the fluffy seeds are easily spread and can be carried long distances to infest new disturbed areas. Tall thistle is a native of the U.S., but can still have negative impacts on agriculture such as lowered forage value of crops, decreased yields, etc.

Management Methods: Tall thistle can be controlled through proper pasture management techniques such as establishment of a competitive ground cover, and avoiding overgrazing. Regular mowing can also help to reduce plant vigor and seed production. Use of herbicides is another viable management alternative, if used properly. Timing of application before the plant sets seeds or is dormant will affect performance. During actively growing or rosette stages, tall thistle is more vulnerable to herbicides. If chemical management methods are chosen, always read and follow label directions closely.

Photo couresy of Weeds of Nebraska and the Great Plains published by Nebraska Department of Agriculture

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