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Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Asterales
Family	Asteraceae
Subfamily	Carduoideae
Tribe	Cardueae
Subtribe	Carduinae
Genus	Carduus

Scientific Name

Carduus acanthoides

Common Name

spiny plumeless thistle, plumeless thistle

Plumeless thistle (Carduus acanthoides)

Author: Michael Moechnig

Adapted from the South Dakota State University Cooperative Extension Weed Control webpage on plumeless thistle

Identification and Life Cycle

Plumeless thistle (Carduus acanthoides) is an introduced biennial in the sunflower family (Asteraceae). Plumeless thistle has deeply divided, crinkly, and hairy leaves. The lobes of the leaves are tipped with long yellowish spines. Leaves have a white midrib. In the second year, flowering stems develop. Stems grow 3 to 5 feet tall, branched, and with leaf like spines. Flowers are 1/2 to 3/4 inch across and reddish purple in color. Plumeless thistle has a heavy branched taproot.

Habitats

Plumeless thistle grows in pastures, rangelands, crops lands, and along roadsides.

Impacts

Plumeless thistle infestations reduce productivity in pastures and rangelands by suppressing growth of desirable species.

Biology and Ecology

Plumeless thistle reproduces by seed. Seedlings emerge from early spring to late fall. Length of time from seedling emergence to flowering can vary from 4 to 22 months. A single taproot develops and stem elongation occur in early May. Flowering begins in early June and continues until mid-August. A single plant can produce up to 9,000 seeds. Seeds are dispersed by wind, have a high germination rate under favorable conditions, and may remain viable in the soil for up to 10 years.

Management Approaches

Since plumeless thistle only reproduces by seed, management approaches should focus on preventing seed production.

Biological Control

There are two biological control agents available for plumeless thistle: the weevils Rhinocyllus conicus, and Trichosirocalus horridus. The thistle head weevil, R. conicus, weevil provides only partial control of plumeless thistle, and has been documented to develop on native non-target thistles. The musk thistle crown weevil, T. horridus, is reported to be very effective against plumeless thistle, although control is reported to take 10 to 12 years. A third species, the tephritid fly Urophora solstitialis was released in Maryland in 1993, but has not been reported to have established.

Mechanical and Cultural Control

Plumeless thistle seedlings are not competitive with established forage grasses. Maintaining a healthy pasture can help prevent invasion by plumeless thistle. Plumeless thistle also does not tolerate regular cultivation of digging. Mowing can be effective if plants are mowed at late bloom, but before seed production occurs.

Chemical Control

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.