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Publications: Noxious Weeds
in Slow Motion: A
talk by Jerry Asher about noxious weeds in the Blue Mountains
Click on a weed to learn about how to find it and kill it!
Alias: St. Barnaby's thistle, cotton tip thistle
- Stems: Rigid and winged by the continuation of the leaf
bases. Grows up to 6 feet tall.
- Leaves: First-year's growth is a rosette of 8-inch deeply
lobed leaves. Stem leaves grow the second year, and are 4 inches
long; lower leaves deeply divided; upper leaves small, narrow,
entire and sharply pointed.
- Flowers: Yellow, head about 1 inch long; solitary at
the end of each branch. Flowering period is from July to September.
Middle and lower bracts have sharp stiff spines up to 3/4 inch
- Fruits: Seeds are tan with white and brown mottling.
Fruit of the marginal flowers dark colored and without bristles,
inner fruits lighter in color with a terminal tuft of white-silvery
Yellow starthistle is a bushy annual or sometimes biennial. It
is covered with loose white cottony wool. It can grow wherever cheatgrass
grows; it infests roadsides, waste areas, and rangelands. It spreads
by seeds that can remain dormant for 10 years. Spines are a deterrent
to grazing, and the plant causes "chewing disease" in
horses which renders them unable to eat or drink.
Control: Effective control requires both weed suppression,
and reestablishment of desirable species.
- Mechanical: Small infestations can be hand pulled, and
disturbed sites should be reseeded with perennial grasses.
- Biological: Seedflies and weevils are being used, but
an effective control is many years away. Cultivation effectively
controls yellow starthistle. Repeated cultivation is required
to control each new seed flush. Repeated mowing can also be effective,
if properly timed. Waiting until the early flowering stage leads
to less regrowth.
- Chemical: Yellow starthistle is becoming resistant to
some herbicides. Contact you local weed board for information
about the ongoing war against this invasive pest.
Report all sightings to your local