Salsola tragus L.
Salsola tragus L.Prickly Russian Thistle
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Description
Russian-thistle is an exotic, annual, erect, xerohalophytic forb. It is highly branched and rounded in form, growing from 1 to 3 feet (0.3-1 m) in height and from 1 to 5 feet (0.3-1.5 m) in diameter. Classic “tumbling tumbleweeds” recognized as an icon of the semiarid American West. The rolling weeds are the mature plants that have autodetached from the roots to begin rolling around the land, spreading seed. The new seedlings and young plants are bright green and grassy. As they develop a more busy form, the stems are red or purple striped and can grow up top 4 ft. (1.2m) tall.Stem
Stems are rigid, typically curved upward, purple-striated or green. Foliage is bluish green and glabrous, but sometimes covered with short, stiff hairs. Bracts are usually awl-shaped, reflexed, and not overlapping at maturity; the margins are membranous and minutely barbed.Leaves
Leaves are alternate, at first dark green and soft and narrow (less than 1/8 in. [0.3 cm] wide). Upper leaves are sharply pointed and 1.25 to 2 in. (3.1 to 5 cm) long.Flowers
From mid-summer to fall small greenish to pink flowers grow from the leaf axil, e3ach protected by a triplet of spine-tipped leaves.Fruit
Seeds: After drying the main stems of the Russian thistle can break off at the ground level under windy conditions, which allows the plants to disperse the seeds as they tumble with the wind. The skeletons will usually persist for at least one year and are typically found along fences and other structures. Russian thistle reproduces by seed, and germination can occur when night temperatures are below freezing and daytime temperatures reach 2º C, but optimal temperature for germination is generally 44º-95º F. Seeds require very little moisture (about 7.5mm of rainfall) to germinate, and after the moisture falls germination will occur within a few hours. To become established seedlings require loose soil. Seedlings that germinate on firm soil seldom survive because the young root is unable to penetrate the soil. Under field conditions, most seeds survive about 1 year, and a few seeds may survive up to 3 years. Plants about 0.5 m tall can produce about 1500-2000 seeds, and larger plants can produce up to 100,000.Images
Photo: Forest & Kim Starr, U.S. Geological Survey, Bugwood.orgMore images of Salsola tragus
Life History
3. HabitatRussian thistle grows best on loose, sandy soils, but will grow in any disturbed sites, waste places, roadsides, fields, cultivated fields, and disturbed natural and semi-natural plant communities. All species in the genus Salsola are native to Europe. The taxonomy of Salsola species in the western United States is complex and not fully understood.
Origin and Distribution
Native to Eurasia, Russian-thistle is distributed throughout most arid and semiarid regions of the world. In North America Russian thistle occurs from British Columbia east to Labrador and south through the conterminous United States to northern Mexico. It is most common in central and western regions of Canada and the United States, and along the Atlantic and Gulf coasts. Limited southern and eastern inland populations occur along waste areas and railroad tracks. Russian-thistle is adventitious in Hawaii.Synonyms
Salsola australis R. Br.Salsola iberica (Sennen & Pau) Botsch. ex Czerep.
Salsola kali L. subsp. ruthenica (Iljin) Soó
Salsola kali L. subsp. tenuifolia Moq.
Salsola kali L. subsp. tragus (L.) Celak.
Salsola pestifer A. Nelson
Salsola ruthenica Iljin
h2. Management Recommendations
Mechanical Controls
Many mechanical strategies are effective in controlling these thistles. Mowing is effective on very young plants. However, older plants will recover by axial branching below the cutting level. Plants should never be mowed after seed set has occurred, as this will facilitate seed dispersal to new areas.Tillage will control both seedling and larger plants. However, tillage increases disturbance, which favors additional germination of seeds. Seed viability appears to be 1-3 years for Russian thistle and is unknown for barbwire or spineless Russian thistle. Therefore, an intensive tillage program that completely prevents seed production for 2-3 years may eliminate these thistles. However, recurrent seed depositions from tumbleweeds blowing in from adjacent areas is highly probable.
Hand pulling of large plants is extremely difficult and may be injurious due to the spiny nature of Russian and barbwire thistle. Always wear gloves if attempting to hand pull these species.
Herbicidal Controls
These thistles primarily occur in dryland agricultural production systems, roadsides, rangelands, and waste areas. This presents the need for several different herbicide strategies. Generally, seedling Russian thistle is not difficult to control with the proper herbicides. However, as plants get older, moisture stress is often likely and herbicide efficacy is greatly reduced.For roadsides, preemergent herbicides applied in the fall can provide season long control. Table 1 provides effective herbicides for roadside Russian thistle control. Post-emergent applications should be made in the seedling stage for effective control. Postemergent applications generally do not provide long term control due to repeated flushes of seed germination following herbicide application. Consult the label for application rates and restrictions.
Russian thistle has documented resistance to chlorsulfuron in Idaho, Oregon, and Washington. In California, a biotype with resistance to both chlorsulfuron and sulfometuron has been found. Avoid developing resistance by using a combination of management strategies and rotating between herbicide modes of action.
Biological Controls
There are two insects that have been approved and released for control of Russian thistle: a leaf mining moth Coleophora klimeschiella and a stem boring moth Coloephora parthenica. Both are available for release in California. Beyond its known establishment in central California, there is little information on the effectiveness of Coleophora klimeschiella. Coloephora parthenica has not been effective in reducing Russian thistle populations. There are a number of possible factors for this, including predation by rodents, spiders, and parasitoids; poor host plant synchronization due to herbivore independent mortality; and a general lack of effectiveness in reducing seed production. Recent taxonomic reconsideration of Salsola tragus and its possible biotypes or subspecies may bring further clarity to the effectiveness of this biocontrol agent.Bibliography
FEISKaufman, S. R. and W. Kaufman. Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species. Stackpole Books, Mechanicsburg, PA. 2007. 264-266 pp.
DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. Volume 1: Aizoaceae to Fabaceae. University of California Department of Agriculture and Natural Resources: 622-632
Young, F. L. and Whitesides, R. E. 1987. Efficacy of postharvest herbicides on Russian thistle (Salsola iberica) control and seed germination. Weed Science 35:554-559
Young, F. L. 1988. Effect of Russian thistle Salsola iberica interference on spring wheat Triticum aestivum. Weed Science 36:594-598.