Common Burdock
Julie Doll* and Dr. Jerry
Doll
Common
burdock (Arctium minus) is one of four burdock species
that have been introduced into North America. Common and great
burdock (Arctium lappa) are the two weedy species. Common
burdock is found in many areas and this has resulted in a plant
with many names. In fact, in early publications there was
confusion in the nomenclature of this species (Gross, et al.
1980). Some of its many identities include lesser burdock, wild
burdock, petite bardane, beggar's buttons, cockle button,
hardock, hurr-bur, cuckold dock, stick button, clot bur, and
wild rhubarb.
Common
burdock is native to Eurasia but is now naturalized in North
America (USDA 1970). It is native to and reached North America
with early English and French settlers. Common burdock was
included on a list of "such plants which are common with us
in England" in the mid 1600's (Gross, et al. 1980). Both
common and giant burdock were found long ago in North America;
however, in the early North American literature giant burdock
was more often sited than common burdock. There are reports that
common burdock was widespread in Pennsylvania by the mid 1800's.
The Native Americans of Western Washington saw common burdock as
being recently introduced in the 1930's. Thus its spread across
the country from New England perhaps took 200 to 300 years
(Gross, et al. 1980).
Common
burdock survived very well in its new North American home, as
seen by its wide distribution across North America. It is
throughout all of the United States except approximately the
southern border and areas around the Great Lakes (USDA 1970).
Every
providence of Canada has common burdock; it is most abundant in
southeastern Canada. In its native home its range includes most
of continental Europe to areas in Scandinavia, eastern Turkey,
and upward into Finland (Gross, et al. 1980).
Biology
Common
burdock is a biennial, thus completing its life cycle in two
years. However, a study at Michigan State University found that,
"Arctium minus plants generally take 4 or more years
to flower under field conditions with moderate to high densities
of grasses and herbaceous dicots" (Gross and Werner 1983).
If conditions throughout the second year are poor, many plants
labeled as biennials will not flower (Gross, et al. 1980).
Different reports indicate flowering times from June to August,
July to October, and July to September. In Wisconsin the most
common flowering time is mid July to the first frost. It appears
that common burdock fertilizes more by an allogamy system, even
though it does have potential to be autogamous. Insects are
attracted to common burdock, even though it has no odor, and
help to fertilize the plants (Gross, et al. 1980).
Most seeds
germinate in early spring; cold treatment of the seeds is not
necessary. A study on the germination of common burdock was done
by mixing fresh seeds with a shallow layer of soil. They were
stored in a container below ground level and cultivated 3
times/year to assess seed survival and the seasonal distribution
of seedling emergence. Few seeds of A. minus persisted
for more than two years (Roberts and Neilson 1981). The weed
seen longevity of common burdock in one report is listed as
10-20 years (Chipenda 1982). One report shows that
"seedling emergence and survival were reduced by the
presence of litter and vegetation" (Gross and Werner 1983).
The number of seeds produced per head varies greatly. Large
differences have been found within a site, between sites, in the
same year and across years. A two year study in Ontario found
that common burdock averaged 11,700 and 13,400 seeds per plant.
(Gross, et al. 1980). Seeds are mature by September and are
spread until the following spring. Research done on seed bank
populations show them to be small and patchy (Gross, et al.
1980).
There is
outcrossing and occasional hybridization in common burdock, as
well as great variation in the natural populations. Taxonomists
recognize up to eight species of burdock. Common burdock is more
variable in Europe than it is in North America. Seven subspecies
and five varieties were found in Europe while three forms under
the subspecies are in North America.
These are:
 A. minus f. pallidum with white petals of the corollas
A. minus f. purpureum with deep purple corollas
A. minus f. laciniatum Clute with sterile flowers and leaves narrow and laciniate
(Gross, et al. 1980).
Habitat
Common
burdock is found in places where the soil is not disturbed;
therefore, it is not commonly found in cultivated areas. This is
due to the fact that it is a biennial, so it needs areas that
are not severely disturbed on an annual basis. Such areas
include: farmlands, pastures, waste places, open or disturbed
woods, road sides, fence rows, barnyards, abandoned fields, and
stream banks. F. Swink has stated that common burdock, "is
especially common in weed patches where there has been previous
cultivation or extensive abuse by livestock" (Gross, et al.
1980). It is found both on moist fertile soils, many with high
soil nitrogen content, and on sterile clay soils. Common burdock
can be found as an isolated plant or in large patches; these
patches are due to a large input of seeds near parent plants.
Many times, not many other plants grow around the patch; some
think this is a result of the large leaves that reduce light at
ground level (Gross, et al. 1980).
As common
burdock is found in such diverse areas, it is no surprise that
it is spreading and in some areas it is listed as an invasive
species. The Wisconsin Department of Natural Resourses Bureau of
Endangered Resources listed common burdock in a column under the
heading: "Listed below are exotic and native species that
are potentially threatening to Wisconsin native habitats. They
either already exist in the state or have become serious
problems in other parts of the Midwest. They may become
troublesome in Wisconsin in the future. Some are already
nuisances in wild lands in the state. Land managers and others
interested in maintaining stable native plant populations should
watch for these potentially problematic species and attempt to
control them before they become a serious threat" (Hoffman
and Kearns 1997).
Importance
In the
past common burdock has seldom been considered a serious weed in
crops because it can be well controlled by cultivation (Gross,
et al. 1980). As more farmers have adopted no-till farming, this
plant is becoming more important and can cause economic yield
losses if not controlled. There are other areas of economic
importance with common burdock. The value of wool is reduced
when the dry heads of the plant cling to the coats of animals (Steyermark
1963), thus it has been listed as a serious threat to sheep (Fortnet
1996). Also, if cows eat large quantities of it, the plant gives
a bitter taste to the milk (Georgia 1931).
Many
microorganisms grow on common burdock, and two microorganisms
have economic importance. Powdery mildew (Erysiphe
cichoracearum DC. ex Merat) affects such species as squash
and cucumbers as well as many species of composites, including Dahlia,
Helianthus, and Chrysanthemum. Root rot (Phymatotrichum
omnivorum (shear) Dug.) attacks cotton and sugar beets, and
as many as 1700 other plant species (USDA 1953, 1960; Westcott
1971).
Common
burdock has long been used as an medicinal herb. There is a long
list of ways in which burdock is helpful in maintaining the
health of the human body. "As an alterative and depurative,
burdock is one of the most effective herbs for cleansing the
blood without the side effect of nausea. It contains 27-45%
inulin as well as an abundance of iron. As a blood purifier, it
is used for arthritis, rheumatism, sciatica, and lumbago.
Burdock can help to reduce joint swelling and calcification
deposits. It promotes kidney function and also helps to remove
toxins through the seat glands. The energy is cooling;
therefore, it is used for "hot"/yang conditions such
as fevers, boils, styes, carbuncles, and infections. Burdock
helps metabolize carbohydrates. Use with sassafras to soothe the
hypothalamus; aids the pituitary gland to adjust hormones and
body weight" (American Health and Herbs 1997). Preparations
made from the root, leaves, and fruits may be used to treat
coughs, asthma, gout, and may serve as laxatives and diuretics.
However, it has been listed as a poisonous plant because of its
diuretic effects (Woodcock 1925). The bristles of the plant also
may cause localized allergic reactions for some individuals.
Common burdock is edible, however, the root of great burdock is
more commonly used as a vegetable. Although not used much as a
food source, The USDA listed common burdock as being "in
reasonably constant demand as a medicinal herb" (Sievers
1930).
Description
Roots The
root system consists of a long, thick, and fleshy taproot. With
time, it may become very tough and hard.
Stem Common
burdock's stem is a crown, close to the ground, the first year.
The second year it is much branched, from two to six feet tall,
hairy, and somewhat grooved or angular.
Leaves The first year a basal,
dense rosette is formed. All rosette leaves die back during the
winter. The rosette needs vernalization; however, one report
shows that some plants flower sporadically after several years
of growth without vernalization. The rosette is a competitive
plant in that its long-petioled, broad leaves shade the
surrounding area, thus leading to openings for the colonization
of burdock seedlings. The second year new leaves are formed and
the leaves are distributed alternately on the stem with the
larger leaves near the base. The leaves are large with a
heart-shaped base. They are hairy and coarse, resembling a clump
of cultivated rhubarb. The undersides of the leaf blades are
white and woolly, and the stout leaf stalks are hollow. The
middle and upper leaves get gradually smaller and have shorter,
more slender stalks and are more pointed towards both ends.
Flower Heads Small red-violet,
very rarely white, disk flowers surrounded by numerous hooked
bracts, or spines, make up the flower head. The flower heads are
globular and numerous and borne singly on short stalks or in
small clusters at ends of branches and from axils of leaves.
They are 1.5-3 cm in diameter and the disk flowers are
surrounded by numerous hooked bracts that later form a bur,
about 1.4 cm in diameter.
Seeds The
head, or bur, of the flower breaks off and scatters the seed.
Many times it gets attached to clothing or animal fur thus
dispersing the seed. The seeds themselves are dark gray to
brownish, 0.25 inches long, and rough.
Management
Many
practices and herbicides maintain and control common burdock;
therefore, with timely weed management activities, common
burdock should be relatively easy to control. The following
herbicides were listed as having excellent control on common
burdock: 2,4-D, MCPA, 2,4-DB, and dicamba. Glyphosate is listed
as having good control (Klingman, et al. 1983). For soybeans,
2,4-D ester applied no less than seven days before planting
should prove effective. 2,4-D can be used in corn with preplant,
pre and post options. Pre plant treatmetns must be applied 7-14
days before planting. Roundup as a burnddown treatment in
no-till systems or in glyphosate-resistant crops gives
acceptable burdock control. Thorough cultivation should kill
most burdock plants. Mowing may prove to be effective method of
control as a study in Michigan showed that "defoliated
plants generally produced fewer seeds/head, fewer heads/plant
and fewer seeds/plant" (Reed and Stephenson 1972, 1973).
There are
13 insect species which attack the common burdock plant. Burdock
moth (Metzneria lappella) is the only one that has been
reported in North America. This insect greatly reduces the
number of viable seeds in the plant, thus it may be a regulatory
factor that influences both the distribution and abundance of
the common burdock populations. There are no active programs
exploring this biological control measure in Wisconsin.
Bibliography
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