IDENTIFICATION
Provincial Noxious. Annual.
Because annual sow thistle blooms from June right through to early
October, the loose clusters of small, yellow, dandelion-like flowers are
a useful clue for recognizing this plant. Mature plants grow to 1 metre
in height with a single upright stem that branches only near the top.
Leaves are deeply lobed and those
close to the bottom end in a large pointed segment.
DAMAGE
A common weed of cultivated crops, annual sow thistle acts as a
host to aphids, several viral diseases, and nematodes. Rapid germination
combined with wind dispersal of seeds allows annual sow thistle to invade
both native plant communities and disturbed sites quickly. It can also
be a problem in marshes, ponds, and riverbanks as it tolerates saturated
soils.
HABITAT
This weed does best on fertile, moist soils in full sunlight. In British
Columbia, annual sow thistle grows on cultivated fields, gardens,
roadsides, riverbanks, and disturbed
sites such as gravel pits and logged areas. It occurs most frequently
in the province's southern coastal regions but is present in all agricultural
regions.
SPREAD
Each plant produces about 6,000 seeds which remain viable
for several years. The tall stalks and lightweight, parachute-like seeds
promote dispersal by wind. Seeds can also be spread by water, and by birds
and animals, attached to fur or feathers.
