FEATURED PROFESSIONAL:
John A. Erixson
Northwest Management,
Inc.
FEATURED PROFESSIONAL:
John A. Erixson
Northwest Management,
Inc.
Spotted Knapweed was introduced from Europe and is widely dispersed in the western United States. Each plant produces up to 25,000 seeds that are dispersed by wind, animals, and people. Seeds can remain viable for up to 8 years.
Spotted knapweed generally is a short-lived perennial, reproducing solely by seeds. The seeds may germinate from spring through early fall. Seedlings emerging in the fall often over-winter as a rosette of leaves, resuming growth again in the spring. The plant grows 2 to 4 feet tall and bears alternate, pale green leaves. The upper leaves are linear in shape. Stems are erect and rough, with slender branches. Numerous flowers are produced from early July through August. Flowers are pink to light purple.
Several biological control agents are available
including root boring beetles and moths, seed head gall flies, and seed
head weevils. The success to these control agents area generally
good; however, re-application is often recommended due to the viability
of the seeds remaining in the soil.
The best spotted knapweed control is prevention.
The plant generally is easy to control with herbicides but an area must
be monitored for several years and retreated.
Picloram (Tordon) at 0.25 to 0.5 pounds
(1 to 2 pints) per acre will control spotted knapweed plants and seedlings
for two to three years. The residual control period may be shorter on gravelly
soils, in wet areas, and where soil organic matter is high. The optimum
application time is during the rosette growth stage in the fall or in the
bud to bloom stage in the spring. Picloram should not be used near
water or where a sandy porous surface and substrata overlie ground water
10 feet or less below the surface.
Clopyralid + 2,4-D (Curtail) will provide
good control of spotted knapweed with less soil residual than picloram
or dicamba. Control is greatest when fall. A follow-up treatment the following
year may be necessary to control seedlings.
For more information contact your County
Weed Control Agent or Chemical Company.
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