Mugwort Unmasked

Mugwort (Artemisia vulgaris) is a stealthy invader, quietly taking over landscapes across North America. Mugwort's ability to invade through both seeds and underground rhizomes poses a serious challenge to gardeners and landscapers. But don’t worry! In this blog, we’ll explore practical tips for controlling this invasive “space invader” and keeping your garden safe.

The Unwelcome Invader

Artemisia vulgaris, commonly referred to as mugwort, wild wormwood, and even felon herb, is one perennial North Creek does not have on our ‘To Grow’ list. In fact, it is listed as an invasive, noxious weed by many authorities across the United States. Common mugwort is native to Europe and Eastern Asia and was brought into North America via multiple methods: for medicinal purposes and spread as a contaminant in ship ballast as well as nursery stock. Mugwort pollen is a common cause of allergies and hay fever, wherever abundant. The plant is a common ingredient in many products, including insect repellents.

Mugwort does well in partial to full sun and moderately dry to mid-moisture soils. It does not persist in wet soils, as it is susceptible to root rot. The plant is often found in high elevation areas, disturbed habitats, meadows, valleys, and roadsides, and can be found throughout much of the northeast, into Canada and extending west to Minnesota and south to scattered areas in Florida. Many counties in Oregon and Washington have also reported large populations.

Distinctive Features of Artemisia vulgaris and Its Native Counterparts

Growing from 2-4 feet tall, Artemisia vulgaris has alternate leaves that appear almost paper, with large pinnate lobes. The leaves are green on the upper surface, with a layer of dense white hairs covers the undersides, and when crushed, are aromatic, giving notes of a chrysanthemum or sage-like scent. The plant features angular reddish-brown stems, which are also covered with short hairs, and has small, yellowish, and altogether inconspicuous flowers that lack petals. Each plant produces many seeds each season, which are commonly yet incorrectly believed to be enclosed in achenes, or single-seeded fruits (think the small brown seeds found on strawberries), they are technically referred to as cypsela, or a dry fruit (one-seeded) formed from a double ovary, of which only one develops into a seed, just like in the daisy family. It is a dry, indehiscent fruit derived from an inferior, bicarpellate ovary, much like corn or wheat.

Of course, this noxious weed is not to be confused with the native Artemisias of North America, of which there are over 30 distinct species. Many of these species can be found west of the Rockies; however, the most widespread species is known as Artemisia ludoviciana, of which there have been selections and cultivars named, such as Artemisia ludoviciana ‘Valerie Finnis’. It's also a known host plant for several species of Lepidoptera, including the American Lady and Painted Lady butterflies. For a full list of Artemisias native to North America, please refer to the Biota of North America Program’s website – bonap.net.

Mugwort’s Dual Nature: Historical Remedies and Modern Challenges

As previously mentioned, mugwort has been used historically to make medicines for centuries and was brought from Europe as early as the 1600’s so settlers could continue that practice in the New World. Having a rather bitter taste, it was used to aid in digestion issues, liver problems and pain, and even high blood pressure. Today, it is even used topically to aid in itching caused by hypertrophic scars (visible, raised scars that can sometimes cause restricted movement of muscles, joints, and tendons). It is important to note that very little research has been done on mugwort in people, and this plant has been known to be toxic when taken in large quantities.

Although an individual mugwort plant can produce up to 200,000 seeds per season, which are largely wind dispersed, its primary method of colonization is via vegetative expansion by aggressively spreading rhizomes. Artemisia vulgaris will readily form large colonies, often via anthropogenic dispersal of the root propagules; plants can regenerate from rhizome fragments as small as 2 cm. Laboratory studies have also found the presence of chemicals that could potentially suppress the growth of nearby plants.

Effective Strategies for Control and Prevention

So, if you have mugwort in your purview, you might be wondering how to control this noxious Space Invader! The good news is that there are multiple methods of ridding your gardens of Artemisia vulgaris, the first one being mechanical control. To prevent seed dispersal, mow plants from late summer to mid-September, before seedhead production and maturation. If mowing after seed has matured in mid-September, it is recommended to collect and bag mugwort cuttings. Hand pulling very young plants in late spring and early summer is also an effective method of stopping the spread, although ideally this is before the formation of rhizomes in the ground. Scouting your garden for weeds on a regular basis is a great way to stay on top of little plants that can turn into landscape-sized problems. And, whenever possible, cover as much bare soil in your garden as possible, as this is where new seedlings like to get established. As the adage goes, an ounce of prevention is worth a pound of cure!

Another method of controlling an already landscape-sized dilemma could be via chemical means. As with any herbicide application, timing is critical, and it is essential to follow the label instructions. Consulting with or hiring a licensed pesticide applicator is recommended. The dense hairs on the mugwort leaf can make it difficult for herbicide to make contact effectively; a surfactant may be advised. Foliar spray of glyphosate applied in late summer may suppress mugwort, but likely will not fully eradicate it. The use of more selective herbicides, such as triclopyr and clopyralid, effectively control Artemisia vulgaris.

 

Sources:
 

1. New York Invasive Species (S) Information. (2019, July 2). Mugwort. Cornell Cooperative Extension & Seagrant New York. https://nyis.info/species/mugwort/
2. University of Connecticut. (2021, April). Invasive Plant Factsheet: Common Mugwort. UConn Extension. https://ipm.cahnr.uconn.edu/invasive_plants_common_mugwort/
3. The Biota of North America Program. https://bonap.net/Napa/TaxonMaps/Genus/County/Artemisia
4. National Center for Complementary and Integrative Health. (2021, July). Mugwort. https://www.nccih.nih.gov/health/mugwort
5. Ladybird Johnson Wildflower Center. (2022, June 11). Artemisia ludoviciana. https://www.wildflower.org/plants/result.php?id_plant=arlu

 

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