Recognize the problem
Asteraceae (daisy family).
names: Blackjack, beggar’s tick, broom stick, cobbler’s pegs, Spanish
buốt, dần sàng, quỷ châm, cúc áo.
or evergreen broadleaved erect herb with a strong taproot (up to 1 m tall); stems
hairless, four-angled, purplish green in colour, simple or branched.
Green, compound with 3–5 leaflets each; leaflet shape variable but usually
egg-shaped with a broader and rounded base tapering towards the end to
spear-shaped [3–7 (–10) cm long and 1–2 (–5) cm wide], leaf margins with
forward-pointing sharp projections or teeth, terminal leaflet always larger
than lateral (side) ones.
White petals, centre yellow (7–8 mm wide), usually borne singly on stalks (1
Black, slender (1-1.5 cm long), ribbed, dry, one-seeded, 2–4 yellowish barbed
bristles or awns at terminal end.
Accidentally as a contaminant, as ornament and for agriculture.
Humid-wet tropical regions.
As seeds by humans, animals, wind and water; the weed has been reported as a
rice crop seed contaminant.
Crops (preferably upland field crops), plantations, pasture, disturbed land,
wastelands, fallow land, gardens, drainage ditches, forest edges/gaps,
riversides, gullies, roadsides and railway lines.
The weed is
known to significantly reduce crop yields. Densities of eight blackjack
plants per square metre in soybean fields can reduce yields by 43%. Dry bean
harvests in Uganda and Peru were reduced by 48% and 18–48%, respectively, as
a result of the presence of B. pilosa.
In Southeast Asia this weed is problematic for those growing maize, cabbage
and perennial and plantation crops such as pineapple and guava. Bidens pilosa is also problematic on un-cultivated land. The weed
is a host and vector to harmful parasites such as root knot nematodes and
tomato spotted wilt virus. The large number of seeds, together with its negative
impact on the growth of neighbouring plants, allows the species to form dense
stands rapidly, displacing crops and native vegetation.