Russianthistle or Common Russianthistle [Salsola tragus L.][SASKR][CDFA list: C] Biocontrol Photographs

Spineless Russianthistle [Salsola collina P.S. Pallas][Bayer code: none][CDFA list: Q] Photographs

Barbwire Russianthistle [Salsola paulsenii Litv.][SASPA][CDFA list: C] Photographs

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GENERAL DESCRIPTION:Noxious bushy summer annuals, with rigid branches and reduced, stiff, prickly upper stem leaves (bracts) at maturity. Introduced from Eurasia.

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SEEDLINGS:Cotyledons and subsequent leaves needle-like. Leaves alternate, but often appear opposite because of short internodes.

MATURE PLANT:Leaves alternate, sessile, linear to needle-like, gradate into rigid, spine-tipped bracts in the inflorescences.

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ROOTS and UNDERGROUND STRUCTURES:Taprooted. Do not form mycorrhizal associations.

Russianthistle: To 1.5 m deep, with laterals spreading to 1.8 m. Plants can extract deep soil moisture that is not available to winter wheat.

FLOWERS:Bisexual, axillary, mostly solitary. Petals lacking. Sepals 4-5, persistent in fruit, typically with wing-like appendages that appear petal-like in Russian and barbwire Russianthistle. Calyx (sepals as a unit) mostly 2.5-3.5 mm long. Stamens 5, extended beyond sepals (exserted). Style branches 2, exserted. Wind-pollinated. Out-crossing and self-fertile.

FRUITS and SEEDS:Utricles (fruiting structures) +/- spherical, 1-seeded, enclosed by persistent calyces. Seeds +/- round and slightly flattened to slightly conical, ~ 1.5-2 mm in diameter, with a thin, gray to brown translucent seed coat (pericarp) and visible dark greenish-brown coiled embryo.

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POSTSENESCENCE CHARACTERISTICS:Plants become gray to brown. Main stems of Russianthistle break off at ground level under windy conditions allowing plants to disperse numerous seeds as they tumble. Skeletons persist for at least one year and are typically found along fences and other structures.

HABITAT:Typically infests sandy soils on disturbed sites, waste places, roadsides, cultivated and abandoned fields, disturbed natural and semi-natural plant communities.


PROPAGATION/PHENOLOGY:Reproduce by seed. Seed appears to require an after-ripening period. Cotyledons are photosynthetic upon emergence.

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MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Seedlings cut just above the cotyledons seldom survive. Properly timed cultivation of seedlings prevents seed production and can control infestations, but cultivation must be repeated until the soil seed bank becomes depleted.

SIMILAR SPECIES:Glasswort [Salsola soda L.] is a slender erect to rounded, glabrous summer annual, to 0.5 m tall. Unlike the Russianthistles, Glasswort remains fleshy at maturity, has calyces 3.5-5 mm long, with inner sepals (facing stem) tubercled and outer sepals with wings less than 1.5 mm long. It is an introduced weed of mudflats and saltmarshes in the San Francisco Bay region. Although flowers and fruits resemble those of Russian and barbwire Russianthistle, Mediterranean saltwort [Salsola vermiculata L.][SASVE][CDFA list: A] is easily distinguished by its shrubby perennial habit and oblong to ovate leaves with rounded tips. It is an uncommon weed of disturbed rocky slopes and flats, often on clay soils, in the Temblor Range (se San Luis Obispo and possibly cw Kern cos.). To 1000 m (3300 ft). Introduced from Syria in 1969 as an experimental range plant. Immature halogeton [Halogeton glomeratus (M. Bieb.) C. Meyer] is distinguished from immature Russianthistles by having fleshy cylindrical leaves broadest near the tips and tufts of long white hairs in the leaf axils.

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Prevention: These thistles are part of a complex genus in the Chenopodiaceae family. They are strongly competitive in semiarid areas and are heavily favored by disturbance. They persist in dryland cropping systems, overgrazed rangeland, roadsides, and waste areas. The exact time of introduction into California for Salsola tragus and Salsola paulsenii is uncertain, but may have been near the turn of the century. Salsola collina is not currently present in California, but appears to be increasing its range across the Great Plains.
Tumbleweeds disperse seed over long distances as they are carried along the ground by the wind. Frequently, new infestations appear as a "trail" of tumbleweed seedlings across fields. Skeletons also often collect along fencerows , and subsequent populations can become very dense. One of the keys to preventing spread of Russian thistle is controlling seedlings along both sides of fence rows and along field borders, where tumbleweed skeletons accumulate. Additionally, areas "downwind" of infested areas are most likely to be invaded. In many cases, it is impossible to prevent tumbleweed movement and sensitive areas should be monitored each year for new plants.

Mechanical: 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.

Biological: 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.

Chemical: 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.

Table 1. Effective herbicides for roadside Russian thistle control.

Preemergent Herbicide Post-emergent Herbicides
Bromacil Bromoxynil
Chlorsulfuron 2,4-D amine and ester formulations
Diuron Dicamba
Hexazinone Glyphosate
Isoxaben Triclopyr
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