Gather and burn mowed debris to destroy any seed that has developed. Chemical control. Several herbicides are registered in pasture, rangeland and noncrop areas to control musk thistle.
Apply these herbicides in spring or fall to musk thistle rosettes. Refer to Table 1 for rates and application timings and always read the herbicide label before using the product.
Applications during the reproductive growth stages with these herbicides bud through flowering will not eliminate viable seed development.
Research from Colorado State University and the University of Nebraska shows that chlorsulfuron or metsulfuron prevents or dramatically reduces viable seed formation when applied in spring, up to early flower growth stages. The latest time to apply these herbicides is when developed terminal flowers have opened up to the size of a dime.
Add a good agricultural surfactant at 0. Biological control. The Colorado Department of Agriculture has established a weevil, Trichosirocalus horridus. This weevil attacks the crown area of musk thistle rosettes and kills or weakens the plant before it bolts.
This weevil is being distributed throughout Colorado by the Department of Agriculture. It tends to be more effective than the seed head weevil. The musk thistle seed head weevil, Rhinocyllus conicus, can be found throughout Colorado. The female deposits her eggs on the back of developing flowers and covers them with chewed leaf tissue.
After eggs hatch, larvae bore into the flower and destroy developing seed. The seed head weevil reduces seed production by 50 percent on the average. If used alone, however, it is not an effective management tool.
Certain herbicides or mowing can be combined with the seed head weevil if these are used during late flowering stages. This allows the weevils to complete their life cycle and ensures their presence in subsequent growing seasons. The musk thistle seed head weevil is not being redistributed anymore because it attacks many different species of thistles, including native thistles. That is, allow the control insects to complete their life cycle. Cultural methods that favor desirable plant growth can be combined with chemical or biological control by superimposing proper grazing management and seeding.
Colorado State University, U. Department of Agriculture, and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
We have 6 regions. Learn more about us or about our partners. In late spring an erect stem develops which is usually 80—cm high but occasionally exceeding cm. After stem elongation and the formation of flowering heads the rosette leaves die off. The stem has whitish-green ribs and usually branches about half way up. Mature plants are very stiff and spiny. In early summer, single yellow compound flowers form at the end of each stem or branch.
Lance-like spines surround each flower. The seeds are large, about 6mm long, grey-brown with prominent ribs and a smooth seed coat. There are at least two forms of saffron thistle in WA. The differences between them are obvious at the rosette stage: one form has a narrow leaf and the other a broad leaf.
The narrow leaf form, which is mainly along the Greenough flats, south of Geraldton, appears to germinate more readily than the widespread broadleaved form. There are also distinct differences in the shape of the seed and rate of stem growth. A closely related species, glaucous star thistle Carthamus leucocaulos , is very similar but with pale pink or purple flowers. It is a declared plant and is found only in the Tambellup area. Saffron thistle is an annual plant reproducing only from seed.
Some seeds have a pappus parachute consisting of stiff bristles, but they are too heavy to be carried far by wind. The bristles may aid spread by becoming attached to wool, hair or sacks, but saffron thistle seeds are most commonly spread as a contaminant in seed or grain, or with hay or chaff. The seed may remain dormant in soil for up to eight years, but most seeds germinate within two or three years. The onset of germination is influenced markedly by higher soil temperatures in summer and length of time the seed is exposed to them.
Generally saffron thistle seeds from the northern agricultural areas Geraldton have lower dormancy than seeds from southern infestations Salmon Gums. Legal Status: Prohibited - Control Efforts must be made to prevent seed maturation and dispersal of plants into new areas. Description An aggressive perennial with a vigorous root system that continually produces new shoots, invading new areas and outcompeting other vegetation types.
Grows 2 - 5 feet tall. Stems are usually smooth, but sometimes have short hairs and are slightly grooved. Flowers are purple and pink, occasionally white, and are borne at the end of the stems in clusters. This plant is a prolific seed producer and also spreads by roots. Seedlings emerge as small rosettes in the fall or early spring, eventually bolting into erect branched flowering stems.
Flowers begin to develop in late June, blooming between July and August. This plant is most recognizable in mid-July when flowers change to seedheads with obvious white fluffy tops. Seeds are attached to the "fluff" and can become airborne and spread to new areas.
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