||Summer/winter annual, biennial,
or short-lived perennial
||Fall or Spring
native plant of Europe and eastern Asia was introduced in the U.S.
late in the 1800's. It is said to have saved Scotland from invading
Norsemen when nighttime guards were alerted by cries of pain as
the attacking army walked through the thistle with their bare feet.
thistle quickly invades sunny areas that have been disturbed, but
is suppressed when invading into a healthy system. Once established,
it becomes highly competitive and can crowd out even cheat grass.
Its rapid growth and large size reduce available light for smaller
plants, and draw away other needed resources. Long spines intimidate
animals into eating easier targets. When a scotch thistle dies,
it leaves abundant litter that can smother surrounding plants. The
scotch thistle plant averages 70-310 flowers per plant. Add to that
a potential of 110-140 seeds per flowering head, and you get a bountiful
seed producer. Eighty to ninety percent of the seed can be dormant
for approximately five years. Seeds may be dispersed by water, wind,
animals, and human activities.
plant competes with and decreases desirable forage, and can form
a dense monoculture
stand. It can act as a living barbed-wire fence, preventing
livestock and wildlife access to feed and water.
used for food
and medicinal purposes.
thistle invades disturbed areas where competition has been reduced.
It is best adapted to high soil moisture and is often associated
with waterways in the western U.S. Although high soil moisture (especially
in dry climates) is preferred, it will occupy dry sites as well.
Scotch thistle is often associated with plant communities dominated
by annual weedy grasses (downy brome/cheat grass) and has been known
to invade crested wheatgrass sites. It grows along roadsides, fence
lines, ditch banks, open dry areas, and in pastures. It is rarely
found in gardens and areas cultivated yearly.
of this plant's invasion is the best management. Seeding disturbed
areas with competitive native perennials is best. Control of these
plants must include preventing new seed dispersal for six years.
The best tools for removing infestations are:
• Digging them out by hand or annual cultivation.
• Use of herbicide on young plants prevents seed set (example herbicide:
Curtail, Tordon 22K, Escort, Telar [look
at herbicide label: free search]).
• Grazing young plants with sheep.