Weed of the Week: Burdock
What does tainted milk, tangled fur, intestinal hairballs, and velcro all have in common? That would be the vigorously self-seeding invasive plant known as common burdock (Arctium minus
Common burdock grows in low to mid-elevations in British Columbia and is well known for prickly burs that cling stubbornly to clothing and animals. Its more popular qualities include medicinal and culinary uses, and observation of its hooked spines that led to the invention of Velcro in the early 1940s by Swiss inventor, George de Mestral.
First introduced to North America in the 1700s for its medicinal characteristics, common burdock was a popular trading item between English and French settlers and is one of four burdock species that was introduced into North America. Common and great burdock (Arctium lappa) are the two weedy species.
Burdock’s brownish-green, deep roots are used as a traditional medicinal herb for many ailments, including as a remedy for dry and scaly skin conditions such as psoriasis and eczema, and as a blood purifier clearing the bloodstream of some toxins. In traditional Chinese medicine, burdock is often used with other herbs for sore throat and colds.
Additionally, burdock root oil extract, also called bur oil, is popular in Europe as a scalp treatment applied to improve hair strength, shine and body, help reverse scalp conditions such as dandruff, and combat hair loss.
Despite the practical uses for burdock, there is a down side. The infamous hook-and-loop system on burdock seeds helps them to disperse, hitching rides on passing animals and people, thereby creating new infestations over great distances. Shakespeare describes it well in Troilus and Cressida, when Pandarus says, “They are Burs, I can tell you, they’ll stick where they are thrown.”
Common burdock is a Eurasian, biennial herb that tolerates most soil conditions. Plants are identifiable by wavy, heart-shaped leaves that grow alternately on the stem, and purple, prickly flowers borne in clusters at the top. Burdock typically blooms between July and October. Seeds mature by September and are spread throughout the winter and spring. Various insects pollinate burdock, particularly honeybees, bumblebees and leaf-cutting bees.
Common burdock is considered an invasive plant in BC. Invasive plants grow and spread quickly, outcompeting native plants and causing damage to the environment, economy and our health; they are the second greatest threat to biodiversity after habitat loss.
Though a treat for pollinators, common burdock can seriously disrupt native ecosystems. Although found primarily on disturbed sites, it will spread to natural areas from nearby roadsides, rail tracks, and abandoned fields. Burdock infestations can be found in grasslands and forests, and along roadsides, ditches, stream banks, and pastures.
Reaching heights of 1 to 3 metres, its large leaves can shade out and prevent other plants from growing, having an adverse effect on crop quality. Burdock has been known to reduce the value of wool due to the seed heads entangling in it, and is responsible for tainting milk products if grazed in large quantities. Additionally, burdock plants indirectly affect the development of economically important plants by hosting powdery mildew and root rot.
Reproducing only by seed, each plant can survive up to 4 years, and seeds 2 to 10 years. An average of 100 burs are produced per plant each season, with each bur containing about 40 seeds. Some studies suggest upwards of 15,000 seeds per plant are produced during its life span.
Common burdock is considered a Noxious Weed under the BC Weed Control Act because of its ability to disperse to reduce crop quality, disperse easily, and sicken livestock. The burs can cause irritation if they cling to the eyes, throat, mouth, or the inside of the stomach of livestock. In some cases the seeds must be surgically removed.
Plants may pose a health risk for livestock, but for areas in Asia, particularly in Japan, the taproot of young burdock plants are harvested and eaten by people as a root vegetable. Burdock contains inulin, a natural dietary fiber, and has also been used traditionally to improve digestion.
Burdock may be a health remedy for some and a food choice for others, but ultimately, infestations are a burden to biodiversity in BC, and should be prevented or controlled. In order to remove this problematic plant, the large taproot systems that grow deep underground must be tilled after rigorous mowing. Most broadleaf herbicides are also useful for control. Hand-cutting below the root crown can also be effective.
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