Musk thistle (Carduus nutans), native to Europe, was first reported in the United States in 1853. It grows about 6 feet tall, chokes out forage plants on range and pasture and displaces other desirable plants. Spines on the branches, leaves and flower heads ward off most animals, and cattle won't graze near the weed. Entomologists at the USDA-ARS plan to release an Italian flea beetle, Psylliodes chalcomera, against the musk thistle pending final approval by APHIS. Planned release sites are near DeSoto, Kansas; Comfort, Texas; and Hagerstown, Maryland.
The flea beetle would join the syrphid fly Cheilosia corydon, another Italian insect first released in the U.S. in 1994. Tests conducted at the Rome substation of the ARS European Biological Control Laboratory showed that neither insect will harm artichoke or chicory, relatives of musk thistle. Adult flea beetles feed on the rosette and on leaf and flower buds. Larvae of the syrphid fly feed in the crown or rosette of young musk thistle plants, and on large flower-bearing stems. These insects would join two others already established in several areas --the flower head weevil, Rhinocyllus conicus, and the weevil Trichosirocalus horridus.
A rust fungus (Puccinia carduorum) has also been released in the U.S. for musk thistle control.
Source: IOBC-NRS Newsletter, Vol. 19, No. 2, Summer 1997--from Agricultural Research, Vol. 45, No. 3, March 1997.
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