A winter annual, Carduus pycnocephalus has stems ranging from 8 inches (20 cm) to 6.6 feet (2.0 m), glabrous to slightly wooly.

[3] Flower heads are 2–5 per cluster, densely matted with cobwebby hairs at the base of the phyllaries and spiny towards the tips.

[8] Mowing and slashing are not reliable as the plant is able to regrow and produce seed even at a height of 3 inches (7.6 cm).

[11] Puccinia cardui-pycnocephali is a species of rust (fungus) apparently exclusive to Carduus pycnocephalus.

[14] Chemical control can be achieved with a variety of products, including clopyralid, glyphosate, Diquat, Picloram, and 2, 4-D ester.