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Submodule 3: Economic and Ecological Impacts

Musk Thistle

Musk thistle (Carduus nutans) is a biennial or winter annual native to areas in eastern Europe, southern Russia, and North Africa. It was introduced to the U.S. in the mid-1800’s and has since spread to most states and covers an estimated 7.7 million acres. The weed is adapted to a wide variety soil and climatic conditions. As is common for many invasive plants, musk thistle is found primarily on disturbed lands and along thoroughfares. The plant is highly competitive and can thrive in areas that are already covered with native plants. It has many sharp spines that can deter grazing by livestock and wildlife. Growing conditions largely determine the number of seeds produced per plant, with numbers as high as 100,000/plant reported. Wind, animals, and vehicles can easily spread these seeds. Research has shown that germination of musk thistle seed can be enhanced by musk thistle plant parts in the soil. Infestation size generally increases at a rate of 12-15% yearly, but has been observed to be greater in some areas.

 

Economic Impacts of Musk Thistle

• Musk thistle often reduces production of native forage plants, which reduces land values. In one case in Nebraska, forage grass production increased by 212% after chemical eradication of this weed. While grazing livestock do not usually consume musk thistle, they have been observed eating flowers and seed heads.
• Musk thistle invasions can limit recreational land use.
• Like all thistles, this plant produces a large amount of pollen and airborne plant parts that can cause serious or prolonged allergic reactions in some people.
• In addition, the sharp spines found on the plant can restrict movement for hiking, fishing, and camping in infested regions, thereby decreasing recreational revenues.
• This weed can cause decreased forage production on infested lands, reduced hay values, and diminished access to valuable forage lands.
• While no direct monetary values have been calculated for musk thistle, it is recognized as a contributor to declining land values. It is generally considered financially beneficial to control this weed, even when costs for herbicide are considered.

Ecological Impacts of Musk Thistle

• Native plant growth is inhibited by musk thistle’s superior competitiveness for resources.
• Musk thistle releases chemicals that inhibits surrounding plant growth, called allelopathy. Researchers found that plant extracts inhibited the germination of grasses and other native species.
• This weed is known to threaten species of rare or endangered native thistles in large parts of southern New Mexico.
• After fire, musk thistle often becomes established in place of native grasses and forbs.
• Fortunately, growth of some native grasses is actually stimulated by fire allowing these plants to become established before musk thistle moves in.

(photo courtesy Larry Howery)

 

 

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