Caardus nutans is an introduced weed species that is often found in pastures, prairie ravines and hillsides, fields and roadsides. Musk thistle is often a biennial herbaceous plant in South Dakota and is a highly competitive plant, threatening many desirable forage species.
The first bio-control release in South Dakota was in the early 1970s when the musk thistle seed weevil, Rhinocyllusconicus, was released to control musk thistle. This biological control agent has now spread through many of the musk thistle infested areas across South Dakota. Currently another weevil, Trichosirocalus horridus, that attacks musk thistle rosettes is being investigated.