||Fall or windows of opportunity
starthistle comes from the Mediterranean region of Europe. It is
believed to have been first introduced into America with alfalfa
seed transported to California late in the 1800's.
a thistle by name, it is really a member of the knapweed complex.
This multi-branched plant is highly competitive and can often dominate
a site. It is typically found in open areas associated with annual
single plant has the potential to produce up to 150,000 seeds, depending
on surrounding plant densities and other environmental conditions.
Of the produced seeds, 10% can stay dormant for more than10 years,
90% are viable, and about 60% of the seeds survive and produce seedlings.
Two types of seeds are produced, those with parachute- like plumes
(transported by wind) and those without (fall or travel with the
seed head). Most seed germinate
in the fall, but some can germinate during windows of opportunity
throughout the year.
plants form rosettes from
March to May and then send up flowering stalks, tipped with bright
yellow flowers. Their competitive ability is due to their rapid
growth and nutrient uptake. They have little stress tolerance during
this time and can easily die if their light, water, nutrients, or
space requirements are not met. In the fall, the plants lose their
leaves and leave a standing silver-grey skeleton with cottony-white
seed heads. Seeds are dispersed by birds, humans, animals, whirlwinds,
and vehicle transport.
starthistle completely changes the natural habitat it invades. It
crowds out native plant populations, reduces the number of plant
species found in the area, and accelerates soil erosion. Thick stands
reduce forage production. The large spines can cause serious damage
to animal mouths and eyes. If starthistle is eaten by horses, it
causes "Chewing Disease," a fatal neurological disorder.
flowers provides nectar for honeybees and the mature seeds are a
good source of food for ring-necked pheasant, California quail,
house finches, and American finches.
can be found on rangelands, roadsides, pastures, and fields through
out the western U.S. Although starthistle does not compete well
with sagebrush, it will invade disturbed sagebrush communities.
It favors sites originally dominated by perennial grasses that have
deep loamy soil, south-facing slopes, and an annual precipitation
of 12-25 inches (Winter or Spring).
starthistle must produce a whole new population from seed every
year. Because of this, controlling seed production and dispersal
is the best way to reduce populations. Some of the tools available
• A combination of herbicide application and a reseeding of perennial
grasses has proven effective (example
herbicides: Clarity, Transline, Curtail, Tordon 22K [look
at herbicide label: free search]).
• Hand-pulling in sensitive or small areas. Plowing or mowing in
• Grazing can be used to suppress young plants before their spines
• Burning for 2-3 consecutive years has shown promise in some studies.