Description:
A deep-rooted perennial herb, perennial sowthistle has erect, hollow
stems with bitter, milky juice. The stems, which can be 1 1/2 to
six feet tall, branch only at the top of the plant. The alternate
leaves are variable in size with prickly edges and pointed lobes.
The stem leaves are clasping and without stalks. The bright yellow
flowers occur in heads that can be 1 1/2 to two inches wide when
in full bloom. The flowers, which have five small teeth across the
outer end, open two to three hours after sunrise and close around
noon. The bracts beneath the flower are green and bristly with sticky
hairs. A plant may have 20 heads during the flowering season from
June to September, but usually only a few flowers at the same time.
The oblong, dark-reddish seeds have five lengthwise ribs and a tuft
of white, silky, parachute-like hairs that can carry it in the wind.
- Mechanical:
Depending on the timing and type, tillage can reduce perennial
sowthistle stands. Some existing evidence suggests that mowing
would not be as effective as tillage as a control method. Tillage
at the seven to nine leaf rosette stage seems to work best for
reducing the reproductive capacity of the roots. Depth of burial
and amount of root breakage determine the effectiveness of tillage.
Root fragments left on the soil surface die from desiccation,
and those buried 30 cm or more are unlikely to resprout. However,
roots buried at intermediate depths will produce new shoots. Smaller
root fragments produce fewer, less vigorous shoots (Lemna and
Messersmith 1990).
- Biological:
Domestic animals - Since perennial sowthistle is palatable to
both sheep and cattle, pasturing infested land can be an effective
control method (Lemna and Messersmith 1990).
- Herbicide:
Herbicide control of perennial sowthistle is better when combined
with other control methods because the species is relatively resistant
to many common broadleaf herbicides. Most chemical control recommendations
for perennial sowthistle are for auxin-type herbicides. Amitrole,
dicamba, MCPA amine, and 2,4-D amine have all been recommended
for control at various growth stages (see Lemna and Messersmith
1990 for more details).Refer to the State
Noxious Weed Control Board site
For More Information:
Detailed information about Perennial
Sowthistle is available at the Washington State Noxious Weed
Control Board Web Site. |
