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Federal Noxious Weed
TDA Noxious Weed
TPWD Prohibited Exotic Species
Invasive Plant Atlas of the US

NOTE: means species is on that list.

Silybum marianum


Blessed Milk Thistle

Synonym(s): Milk thistle, spotted thistle, variegated thistle
Family: Asteraceae
Duration and Habit: Annual, Biennial Herb


Photographer: Charles T. Bryson
Source: USDA Agricultural Research Service, Bugwood.org

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.

Native Lookalikes: Currently no information available here yet, or there are no native Texas species that could be confused with Blessed Milk Thistle.

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.

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.

History: Likely introduced as a folk medicine.

U.S. Habitat: Likely to be found in disturbed areas, pastures or right-of-ways.

Distribution

U.S. Nativity: Introduced to U.S.

Native Origin: S. marianum is an annual/biennial herb native to the Mediterranean region.

U.S. Present: 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

Distribution in Texas: Distribution in Texas is limited and only known to be present in northeast and central Texas.

Mapping

Invaders of Texas Map: Silybum marianum
EDDMapS: Silybum marianum
USDA Plants Texas County Map: Silybum marianum

Invaders of Texas Observations

List All Observations of Silybum marianum reported by Citizen Scientists

Native 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.

Text References

Online Resources

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.

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.

Search Online

Google Search: Silybum marianum
Google Images: Silybum marianum
NatureServe Explorer: Silybum marianum
USDA Plants: Silybum marianum
Invasive Plant Atlas of the United States: Silybum marianum
Bugwood Network Images: Silybum marianum

Last Updated: 2014-03-31 by Justin Bush, Lady Bird Johnson Wildflower Center
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