Musk thistle · Carduus nutans
(L.) · (aka
nodding thistle) is a native of Europe. It was first recorded in the
United States in 1852 at Harrisburg, PA. The first documented report of
musk thistle in Kansas was from a collection made in Washington County
inI 1932. Musk thistle is a noxious weed in all counties in Kansas.
Kansas law requires that all persons and organizations prevent the
spread of and eradicate it on all lands owned or supervised by them.
Any livestock feed material containing musk thistle seed shall not be
sold, offered for sale, bartered or given away except to processors or
where the grain or hay will be consumed on the same farm where grown.
Musk thistle normally requires two years to complete its life cycle
(i.e. biennial or winter annual). Occasionally, the plant completes its
life cycle in one growing season (i.e. summer annual). The typical
biennial musk thistle exhibits itself the first year in the form of a
rosette, a cluster of tightly packed leaves laying flat on the ground.
Rosettes vary in diameter from a few inches to three feet. Musk thistle
overwinters as rosette. During the rosette stage (either fall or
spring), musk thistle is most susceptible to chemical control. In its
second year of growth, the musk thistle plant will leave the rosette
stage as its stemelongates (bolts) toward the 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
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.
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 1½ – 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.
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.
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.