By Mary McKinney with Park County Weed and Pest

Common Mullein Verbascum Thapsus

Common Mullein is native to Europe, Northern Africa, and Asia and was brought to North America as early as the 1700s. Historical uses were primarily medicinal in nature. Medicinal uses included relief of respiratory disorders, expectorants, antibacterial, anti-inflammatory, and for pain relief such as earaches. Early settlers in Virginia also used the leaves of common mullein as a piscicide, or fish poison.

Common Mullein is a biennial noxious species, usually found in wastelands, ditches, roadsides and other disturbed areas with plenty of sunlight. It does adapt to most soil types but prefers dry, sandy, or gravelly soil, but don’t be surprised to find it in pastures, meadows or in the forest. Because of its biennial nature, some years we see a lot of it here in Park County. For instance, recent disturbances over the last few years along the Northfork Highway have spread the seeds and created an opportunity for seeds to be redistributed along that corridor where they have found a habitat suitable for growth.

Identification of Common Mullein

There are not many species in our area with similar characteristics, most notably Mullein's super hairy, almost fuzzy felt-like hairs covering the leaves and stem. Those hairs help aid in the loss of water through evapotranspiration. Plants are tap-rooted and reproduce only by seed. 1st year basal rosette leaves may reach 20 inches long and 5 inches wide and are quite hairy (fuzzy) on both sides. During the 2nd year the plant bolts and produces a single flowering stem (also hairy) that may grow up to 10ft tall. Stem leaves lack petioles, are alternate and get smaller towards the inflorescence during the second year.

Short lived, five-petal yellow flowers are produced on a long terminal spike (sometimes branched). Flowers mature from the bottom and progress upwards. Flowering occurs from June through August. Flowers are only open for a day from dawn to midafternoon. Flowers are frequented by several pollinators including hover flies, long and short
tongue bees but can self-pollinate as well. Each plant can produce over 100,000 seeds. Seeds are toxic and can remain viable for up to 100 years! The plant's leaves, in addition to the seeds, have been reported to contain rotenone, (fish toxicant or piscicide) and coumarin although quantities are unknown. It is common to see the dead
flowering spikes of mullein for several years after they have died.

ECOLOGICAL THREAT

This aggressive invader, once established, out competes native species for resources. It can dominate a site quickly due to the large number of seeds produced, seeds’ long-term viability, and its adaptability to different site characteristics. Established populations of common mullein can be extremely difficult to eradicate. Common mullein provides little to no nutritional value to native animal species or domestic livestock; however,
there is conflicting data as to whether or not wildlife consumes this species.

*(noxious species are invasive species that can cause ecological and/or economic harm and allow for control) *

Control of Common Mullein-Integrated Management

Prevention: may be the easiest. Limiting disturbances and using weed seed free end products such as soil, mulch and gravel may be the most effective and economical method of common mullein control. Monitoring previously disturbed sites and re-seeding to perennial grass is a common strategy. Vigilance is key!

Physical or Mechanical: Think labor intensive. Physical control methods may be an effective method of removing small aboveground common mullein populations. Removing plants below the basal leaves is effective. Clipping seed heads will reduce the number of seeds in the seed bank. Dispose of in the landfill or contact Weed and Pest.

Biological: There have been no purposeful introductions of common mullein biological control agents. Weevils were accidentally introduced in North America. In Park County, releases of the seed feeding weevil (Gymnaetron Tetrum) have been done and will be monitored for results. Weevils can destroy all seeds within a capsule but rarely infest all capsules. Weevils may destroy up to 50% of common mullein seeds.

Chemical: 1st year rosettes are easily killed by herbicide, but 2nd year plants are more resistant. However, a review reports that common mullein's extreme hairiness reduces the effectiveness of herbicides. Aiming herbicides directly into the center of the rosette may increase herbicide effectiveness. Use of a high-quality surfactant is also necessary. Always follow label requirements. They are the law. Contact Park County Weed and Pest for herbicide recommendations.

References and further reading:
https://www.fs.usda.gov/database/feis/plants/forb/vertha/all.html

Fact Sheet: Common Mullein (2005) Plant Conservation Alliance’s Alien Plant Working
Group. https://www.invasive.org/alien/fact/pdf/veth1.pdf

https://pfaf.org/user/Plant.aspx?LatinName=Verbascum_thapsus

(https://www.fs.usda.gov/database/feis/plants/forb/vertha/all.html#BOTANICAL%20AND
%20ECOLOGICAL%20CHARACTERISTICS)

Kivilaan, A.; Robert S. Bandurski (October 1981). "The One Hundred-Year Period for Dr.
Beal's Seed Viability Experiment". American Journal of Botany. 69 (9): 1290–1292.