Centaurea maculosa / spotted knapweed
Pictures:
Photos By: Brian Edsall, WHS student
Description's
Root: The
knapweed plant has a stout taproot.
Stems/ leaves:
Spotted knapweed plants have alternately arranged, pale green
leaves that measure about 2.5 to 7.5 cm (1 to 3 in.) long. The basal
rosette leaves (the bottom ring of leaves) are deeply divided into lobes;
steam leaves have fewer lobes and are smaller toward the branch tip.
Flowers: Buds
form at the ends of the main stem and upper branches. The flowers
are pink and light purple and occasionally white.
Spotted knapweed seed heads are distinguished from those of diffuse knapweed
by the center spine of the bracts which is much shorter tan diffuse and
which generally has a black spot near the tip.
Fruits/seeds:
Spotted knapweed is a prolific seed producer.
Between five and 1,200 seed heads are produced by each mature plant, each
seed head produces up to 30 seeds. The smooth seeds are brown black
with pale, longitudinal lines. Seeds can remain viable in the soil
for five or more years. Most seeds germinate in the spring, but those
that germinate in the fall produce over wintering rosettes.
Methods of reproduction/spread:
This species reproduces by seed only.
Life style/habits/life duration:
Spotted knapweed is an aggressive biennial or short lived
perennial that grows from 0.3 to 1m (1 to 3 ft.) tall. Seedlings
emerge from spring through early fall. Plants bolt (the flowering
stems quickly grow) in early May and flower from late June to October.
Montana infestation/ history:
Spotted knapweed was first reported in the western
parts of Montana in the 1920's. Since then it has spread to every
county. Areas in Montana were there is high probability that spotted
knapweed will grow, are based upon the conditions found in 116 knapweed
infestations.
Environments favorable to
infestation: Disturbed ground and drier
area's are the most common.
Impacts:
Spotted knapweed is the number one problem weed on the western
range land. Infestations cause soil erosion, decrease biodiversity,
and reduce forage for wildlife and livestock.
Comments:
Spotted knapweed is usually distinguished by its black-tipped
bracts on the flower heads with pinkish-purple flowers, although these
characteristics can be seen in some diffuse knapweed plants. The
two species are differentiated by the length of the center spine of the
bract: center spines of spotted knapweed bracts are short while the
center spines of diffuse knapweed are long.
Native range/ probable entry
into N. America: Central Europe, and
east to central Russia. The plant may have come into the U.S as a
contaminant in alfalfa seed.
Methods of control
" How to"
Chemical
Cultural- list/ description
Biological- list/ description
other