mature,
flowering plant with a large fleshy taproot that is corky and hollow
near the ground surface. Chemical control is less effective during
the bolted stage and chemical susceptibility continues to decline as
the plant reaches maturity.
Leaves
The leaves of musk thistle are deeply lobed, hairless, and
are dark green with a light green mid-rib. A silver-gray
leaf margin is characteristic of each spine tipped lobe.
The leaf base extends down the stem to give the plant a winged
appearance.
Flower (Heads)
Musk thistle is the first of the Kansas thistles to bloom in the
spring. Flowering begins in mid-May and continues through early
July. Each head consists of many tightly packed rose to purple
colored flowers encased in a series of spine-tipped, green bracts.
The terminal (uppermost) head is 1˝- 3 inches in diameter, solitary,
and generally bent over or nodding. The mature plant is generally
branched, with each lower branch producing one or more heads.
Flowering begins with the terminal head and progresses downward.
Musk thistle heads are distinguished by their"powder puff"shape.
Other Kansas thistles have"shaving brush"shaped heads.
Seeds
Disposal of seeds begins approximately 30 days after blooming
of the head. Seeds are straw-colored, oblong, and 1/8 inch in
length. The seeds are attached to parachute–like hairs (pappus)
which allow for their dispersal by wind currents. The potential
for seed production is enormous. Large plants can potentially
produce 15,000 seeds with approximately 50% of those being viable.
Mechanical / Cultural / Chemical Control
Musk Thistle can be effectively controlled when treated with an
approved herbicide before the flower stalks bolt. Hoeing or tillage
will control Musk Thistle. If hand-digging, dig the root at least
two inches below ground level and remove all soil. Repeated mowing
of Musk Thistle will reduce seed production.
- 2,4-D Amine- 2.5 gallon containers.
- feedlots and waste areas
- pastures and CRP
- cool and warm season hay fields
- can be used as a tank mix with other products
- kills Musk Thistle and other broadleaves,
but does not kill grass.
- Tordon 22K- 1 gallon containers.
- restricted use product, must have a certification
number to purchase
- should be used as a tank mix with other products
- feedlots and waste areas
- cool and warm season hay fields
- pastures and CRP
- kills Musk Thistle and other broadleaves, but does
not kill grass. Has long residual.
- Escort- Late season thistle control
where Sericea Lespedeza is also a problem.
- must be commercially applied
- for larger tracts
- kills Musk Thistle and other broadleaves, but does
not kill grass.
- Speedzone- 1 quart containers.
- yards and small grass areas
- spot applications
- kills Musk Thistle and other broadleaves, but does
not kill grass.
- Musk Thistle Weevil / Rhinocyllus conicus
- bio-control insect that feeds on Musk Thistle seed
heads
- should be used in conjunction with other control
measures
Factors for Prevention and Control
- The first line of defense against musk thistle should
be proper grazing management.
- Fertilization of cool-season forages is also an important
practice in reducing a musk thistle invasion.
- Purchase feed gain or hay from reputable neighbors or
dealers.
- Properly clean equipment before leaving an infested field.
- Apply herbicide(s) when musk thistle plants are in the
rosette stage and rapidly growing with favorable soil
moisture.
- For ground applications apply herbicide(s) with 10 to
20 gallons of carrier per acre.
- For aerial applications apply herbicide(s) with 3 to
5 gallons of carrier per acre.
- Retreat with the herbicide(s) or cultural treatment to
prevent seed production and reduce new infestations.
For further information, contact the Shawnee
County Weed Department.
