© Benaki Phytopathological Institute
Damalas
et al.
18
many single-seeded, brown, oblong, angu-
lar fruits having a short, stiff bristle at one
end. Flowering stems emerge in June and
flowers are formed from late June up to Oc-
tober in Orestiada. Flowering usually takes
place during the second year, but occasion-
ally flowers are not formed until the third or
fourth year of growth (Gross and Werner,
1983). When burs dry, their hooked bristles
attach to fur or clothing and the bur sepa-
rates from the plant, thereby dispersing the
seeds. Dispersal of burs and seeds begins in
September and continues throughout win-
ter and into the following spring.
Common burdock can be often con-
fused with other species in various growth
stages. To avoid confusion with other spe-
cies, the following information should be
taken into account. At the cotyledon stage,
common burdock may show some similar-
ity with giant ragweed (
Ambrosia trifida
)
at the same growth stage, but the cotyle-
dons of giant ragweed are obviously smaller
(Alex, 1992). At the seedling stage, common
burdock can be easily confused with broa-
dleaf dock (
Rumex obtusifolius
) and curly
dock (
Rumex crispus
), but these two spe-
cies do not have hairs on the underside of
the leaves (Alex, 1992). At the rosette stage,
common burdock resembles a popular gar-
den vegetable, i.e. the cultivated rhubarb
(
Rheum rhabarbarum
), but the leaves of the
latter do not have wooly undersides and
its petioles are solid and tinged red (Alex,
1992). Common burdock flowers are simi-
lar to those of bull thistle (
Cirsium vulgare
),
but the stems and leaves of the latter have
spines and its leaves are deeply lobed (Alex,
1992). Common burdock is similar in appear-
ance to great burdock (
Arctium lappa
), ex-
cept that the latter grows taller, has larger
flower heads arranged in clusters with flat-
tened upper surfaces and the petioles of
basal leaves are not hollow (Alex, 1992).
Common burdock is not considered to
be a serious weed in cropland, because it
can be easily controlled by cultivation, par-
ticularly in the first year of growth. Gross
et
al.
(1980) and Van Vleet (2009) reported that
the plant does not tolerate frequent cultiva-
tion (Gross
et al
., 1980; Van Vleet, 2009). How-
ever, as more farmers adopt no-till farming
practices, this weed can become important,
even causing yield losses, if not controlled.
Other areas of economic damage by com-
mon burdock reported include the reduc-
tion of wool value, when the dry heads of
the plant cling to the fur of sheep and the
bitter taste of milk, when the cows eat large
quantities of the plant (Gross
et al
., 1980). In
addition, certain microorganisms can grow
on common burdock, with two of them hav-
ing major economic importance: i)
Erysiphe
cichoracearum
(powdery mildew) that usual-
ly affects squashes and cucumbers as well as
many species of Asteraceae, such as
Dahlia
,
Helianthus
and
Chrysanthemum
, and ii)
Phy-
matotrichum omnivorum
(root rot) that at-
tacks mainly cotton and secondarily numer-
ous other crops. Root-knot nematodes of
the genus
Meloidogyne
, which attack many
cultivated plants and especially legumes,
have been reported from
A. minus
(Gross
et
al
., 1980).
Based on reports from the so-called
grey literature, common burdock can be
controlled by the application of sever-
al types of herbicides, including atrazine,
2,4-D, 2,4,5-T, 2,4,5-TP and MCPA with treat-
ments of plants preferably in the first year
of growth (Nawrocki, 2010). Glyphosate-
based herbicides are effective as well as oth-
er herbicides, such as clopyralid, clopyralid
plus triclopyr, aminopyralid, picloram and
dicamba when applied preferably between
the rosette stage and the flowering stage
(Klingman
et al
., 1983; Van Vleet, 2009). Also,
mowing can assist in eliminating seed pro-
duction, when repeated multiple times per
season. Defoliated plants have been found
to produce fewer seeds per head, fewer
heads per plant and thus fewer seeds per
plant (Reed and Stephenson, 1973). Infes-
tations can be controlled by digging to re-
move the plant and as much of the taproot
as possible. Plants will re-grow, unless the
taproot is removed (Van Vleet, 2009).
In conclusion, this preliminary study
could be a useful guide to determine com-
mon burdock occurrence in Orestiada,
