Charles T. Bryson,
USDA Agricultural Research Service, Bugwood.org
Family: Asteraceae
Synonym(s): Milk thistle, spotted thistle, variegated thistle
Duration: Annual, Biennial
Habit: Herb
Listed by:
Invasive Plant Atlas of the US: 1
Federal Noxious Weed: 0
TDA Noxious Weed: 0
TPWD Prohibited Exotic Species: 0
Description: A robust, branching annual/biennial growing from 2 to 6 feet in height. Flowerheads are presented in many small florets in heads from 2-6 inches wide. Spine-tipped, bracts are present around heads in several rows up to 2 inches in length. Leaves are somewhat hairy, presenting lobed basal leaves from 8-20 inches in length. Leaves are variegated green and white and very spiny.
History: Likely introduced as a folk medicine.
Biology & Spread: S. marianum reproduces by seed, producing over 6,000 seeds per plant annually. Seeds are spread by erosion, human activity, rain or livestock. Seeds can remain viable for over 9 years in the soil.
Ecological Threat: Milk thistle is poisonous and can cause nitrate poisoning in cattle and sheep. Well established infestations reduce forage in pastures and rangeland settings. Also, their large rosettes (up to 3 feet in diameter) block light to nearby vegetation and suppress germination and growth. Plants can reach 2-3 m in height in dense stands, and plant skeletons continue to stand for several months, keeping an area bare of other vegetation.
US Habitat: Likely to be found in disturbed areas, pastures or right-of-ways.
Distribution
US Nativity: Introduced to U.S.
Native Origin: Mediterranean region.
US States: AL, AR, AZ, CA, CO, CT, DC, GA, IN, LA, MA, MD, MI, MS, NH, NM, NV, NY, OH, OK, OR, PA, TN, TX, VA, WA, WV
Resembles/Alternatives:
Management: For small infestations, milk thistle can be controlled by pulling or digging up rosettes or the bolted plant before seed heads develop. Use a shovel to cut the taproot under the soil so the plant will not resprout.
For larger infestations, foliar applied, broadleaf herbicides are most effective when applied during active plant growth. 2,4-D, metsulfuron methyl or aminopyralid are known to be effective and will not harm grasses if properly applied. Non-selective herbicides such as glyphosate are effective, but will harm grasses.
USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
Listing Source
Texas Department ofAgriculture Noxious Plant List
Texas Parks and Wildlife Department Prohibited Exotic Species
Invaders Program
Federal Noxious Weed
Union of Concerned Scientists
United States Forest Service Southern Research Station
Text References
Noxious Weeds of Australia. W. Parsons and E. Cuthbertson, 1992, pages 229–233. World Weeds: Natural Histories and Distribution. Holm et al., 1997, pages 775–786.
Sindel, B.M. 1997. "The persistance and management of thistles in Australian pastures." New Zealand Plant Protection Society.
Whitson, T.D. (ed.) et al. Weeds of the West. Western Society of Weed Science in cooperation with Cooperative Extension Services, University of Wyoming, Laramie, Wyoming.
Data Source
Last Updated: 2024-01-24 by ARMO