Russianthistle or Southern Russianthistle [Salsola australis R. Br.][SASKR][CDFA list: C] Biocontrol Photographs

Spineless Russianthistle [Salsola collina P.S. Pallas][Bayer code: none][CDFA list: A (proposed)] Photographs

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

SYNONYMS:

• Russianthistle: tumbleweed, Russian tumbleweed, tumbling weed, windwitch, witchweed, common saltwort, Salsola australis R.Br., Salsola iberica (Sennen & Pau) Botsch, Salsola kali L. var. tenuifolia Tausch., Salsola pestifer Nelson. The synonymy of this taxon is complex, and correct use of some scientific names is currently uncertain. Only frequently used synonyms are listed.
• spineless Russianthistle: tumble thistle

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

• Russianthistle: Plants are an alternate host for the beet leafhopper (Circulifer tenellus) that can carry the virus causing curly-top of sugarbeets, tomatoes, melons, and many other crop and native plants. Immature plants can provide extra forage for livestock on arid rangelands. However, under certain conditions, such as heavy nitrogen fertilizer application, nitrates or oxalates can accumulate to levels poisonous to sheep. Biocontrol has not been successful in California. Russianthistle consists of 2 variants or types in California. Currently designated type A and type B, the two types differ in chromosome number (A: 2n = 36; B: 2n = 18), spinyness, fruit size, calyx characteristics, seed weight, and pubescence. Both types hybridize with barbwire Russianthistle. Plants with intermediate characteristics can be found in regions where both species occur. Introduced into South Dakota around 1874 in flax seed from Russia.
• spineless Russianthistle: No infestations are currently known in California, but seed has been found as a contaminate of commercial birdseed. Widespread in the Midwest and appears to be expanding range. First reported in the Midwest in 1958.
• barbwire Russianthistle: Closely resembles, hybridizes with, and is often confused with Russianthistle. Plants rarely host the beet leafhopper. Thought to have been introduced to the Southwestern U.S. at the turn of the century, but unrecognized until 1967.

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

• Russianthistle: Cotyledons 10-35 mm long. Subsequent leaves fleshy, soft, weakly spine-tipped. Stems slender, flexible, typically with reddish-purple longitudinal striations. Immature plants taller than wide, with lateral branches ascending and shorter than the main stem.
• spineless Russianthistle: Subsequent leaves pliable, +/- fleshy, with a soft bristle at the apex.
• barbwire Russianthistle: Cotyledons similar to those of Russianthistle. Subsequent leaves resemble those of mature plants. Stems thick, +/- rigid, without purple striations. Main stem shorter than lateral branches. First 4 lateral branches often form a cross-shaped pattern and are nearly prostrate, with the tips curved upwards. Immature plants are wider than tall and appear mounded at an early stage.

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

• Russianthistle: To 1 m tall, usually height +/- equal to width or taller than wide. Stems rigid, typically curved upwards. Foliage +/- blue-green, glabrous (mostly type B) or covered with short, stiff hairs (mostly type A). Leaves fleshy to leathery, 8-52 mm long, mostly 0.5-1 mm wide, sharp-pointed to spine-tipped. Bracts +/- awl-shaped, reflexed, not overlapping at maturity, with membranous, minutely barbed margins.
• spineless Russianthistle: To 1 m tall. Stems green and white striated, straight, erect to ascending. Foliage +/- glabrous, covered with minute papillae. Leaves to 5 cm long, pliable, +/- succulent to leathery, with a soft bristle at the apex and expanded bases that extend a short distance down the stems (slightly decurrent). Bracts lanceolate, appressed to stems and strongly overlap one another.
• barbwire Russianthistle: Typically to 0.5 m tall, wider than tall. Foliage +/- yellow-green, glabrous or covered with minute papillae. Leaves fleshy, thick, stiff, spine-tipped, 5-32 mm long, 1-1.5 mm wide, often curved away from the stem (recurved) near the tip, covered with short hairs or minute papillae. Bracts resemble those of Russianthistle.

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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.

• Russianthistle: July-October. Typically male flowers develop in early July. Bisexual flowers develop from about mid-July (type B) to early October (type A). Sepal tips acute, +/- lax, not spine-like. Sepal wings fan-shaped, 0.5-2.5 mm long, usually minutely toothed to scalloped along the margins, translucent, often pinkish to deep red with conspicuous veins, folded (type A) or open (type B).
• spineless Russianthistle: Summer/fall. Sometimes with gall-like flowers in leaf axils of the lower portions of plants. Flowers +/- hidden by 2 large, fleshy, spine-tipped bracts. Sepal wings lacking or narrow, mostly less than 1 mm long, with minutely irregular-toothed margins.
• barbwire Russianthistle: June-September. Typically flowers 2-3 weeks earlier than Russianthistle. Sepal tips often stiff, erect, usually spine-like. Sepal wings similar to those of Russianthistle, but larger (2.5-4.5 mm long), typically flat, with entire to minutely irregular-toothed margins.

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.

• Russianthistle: Fruits 4-10 mm diameter, including sepal wings. Fruits of type A are generally smaller than type B fruits. Sepal wings flat (mostly type B) or folded (mostly type A). Type A seeds typically ~ 2-2.5 mg/seed, type B ~ 1.25-1.75 mg/seed.
• spineless Russianthistle: Fruits 3-5(7) mm diameter including sepal wings when present, hidden by 2 large, fleshy, spine-tipped bracts.
• barbwire Russianthistle: Fruits 7-12 mm diameter, including sepal wings.

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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.

DISTRIBUTION:

• Russianthistle: Common throughout California, but largest infestations occur in the southern region of the state; to eastern North America, Mexico. To 2700 m (8860 ft.).
• spineless Russianthistle: Currently not known to occur in California. Probably to 2000 m (6560 ft)
• barbwire Russianthistle: Common. Mojave Desert, eastern Sierra Nevada, northern Western Transverse Ranges; to Utah. 700-1800 m (2300-5900 ft).

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

• Russianthistle: Most seed germinates the spring following maturation. Seed can germinate when night temperatures are below freezing and daytime temperatures reach 2º C. Optimal temperatures for germination are between 7 and 35º C (45 and 95º F). Germination requires little moisture (0.3 inches of rainfall) and occurs within in a few hours. Successful germination requires loose soils. Seedlings that germinate on firm soil seldom survive because radicles are unable to penetrate the soil. Seed in the field typically remains viable for only 1 year, some up to 2 years, rarely to 3. Plants about 0.5 m tall can produce about 1500-2000 seeds, and large plants can produce up to 100,000. Seed disperses when plants break off at ground level and tumble with the wind. Seedlings attain optimal emergence from litter or soil depths to 1 cm, but can emerge from soil depths to 6 cm.
• spineless Russianthistle: No information available.
• barbwire Russianthistle: Reproductive biology similar to that of Russianthistle, but seed appears to require less after-ripening time and germinates over a broader range of temperatures. Most seed disperses near the parent plant, and plants typically do not become "tumble weeds."

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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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CONTROL METHODS:

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 australis 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.

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