Salsola tragus L. = S. iberica (Sennen & Pau) Botsch. ex Czerep.
Other common names: Russian tumbleweed, Russian cactus, tumbling Russian-thistle, glasswort, burning bush, saltwort, prickly glasswort, wind witch, tumbleweed
Family: Goosefoot family, Chenopodiaceae
Habit: Erect, branched summer annual herb
Description: The seedling stem is striped with reddish-purple streaks. Cotyledons are fleshy, needle-like and 0.8–2 inches long by less than 0.1 inch wide. The first true leaves of the seedling appear opposite and are fleshy, similar in size and shape to the cotyledons, and tipped with spines. The leaves become smaller, flattened and less fleshy as the plant grows. Mature plants are 0.5–4 feet tall, often as wide as tall, profusely branched and bush-like in appearance. Stems have short, stiff hairs (or are occasionally smooth) and have reddish-purple streaks. The stems become stiff and dry as the season progresses. Leaves are alternate, hairless or with short hairs, thin and linear or needle-shaped, 0.25–2.5 inches long by 0.04–0.25 inch wide, and have a stiff, prickly spine at the tip. Mature plants may break at the base and become a tumbleweed. The root system is a long taproot. Small, petal-less flowers develop in the leaf axils on the upper portions of the stem between a pair of 0.02 inch-long, spine-tipped bracts. As the flower matures, five pale green to red, petal-like, membranous sepals enlarge to 0.15–0.3 inch wide and surround the single developing seed. The seed is conical, gray-brown and 0.2–0.3 inch in diameter.
Similar species: Kochia [Bassia scoparia (L.) A.J. Scott] has similarly striped stems and a similar growth habit to Russian-thistle. Kochia leaves, however, are broader, lack spines and have dense, greyish hair on all surfaces, while the leaves of Russian-thistle are hairless or have only short hairs and are spine-tipped.
This is the dominant broadleaf weed in dryland grain production areas, and heavy infestations can prevent adoption of less competitive rotational crops such as spring peas or canola. Because Russian-thistle primarily emerges in early spring, rotation with late spring and summer crops allows most of the previous year’s seeds to emerge and be killed by tillage before planting. Similarly, due to the very early season emergence of Russian-thistle, a brief fallow (one to two weeks) before planting an early season crop can help control the weed. Because Russian-thistle is intolerant of shade and relatively slow growing, crop competition is an important control mechanism. Thus, choosing a sowing time to maximize early crop growth rate, choosing competitive cultivars, increasing crop density and decreasing the distance between grain rows all help reduce the competitiveness of the weed. Accordingly, Russian-thistle emergence and growth is suppressed more by a crop of established winter wheat than by spring wheat. Also, inclusion of green manure crops such as yellow sweet clover into the rotation can suppress this weed.
Conventional tillage reduces the abundance of this species, whereas it thrives in no-till or reduced tillage fields with surface residue cover.
Russian-thistle can accumulate over 93% of its total dry matter production after grain harvest, so control of this weed after harvest is essential. Shallow undercutting with wide, low-pitch V-blades after grain harvest can completely prevent seed production while retaining 90% of the stubble for prevention of erosion.
Close mowing of newly emerged seedlings will kill most of them. Mowed or rotationally grazed forages compete with the weed, and mowing and treading kills plants and helps prevent seed production by those that remain.
Origin and distribution: Russian-thistle is a native of Russia that was introduced into South Dakota in flax seed in the mid 1870s. It presently occurs throughout the United States and southern Canada, except in the Deep South. In Eurasia its range extends from China through most of Europe and into North Africa. It has been introduced into southern Africa, Australia and parts of Central and South America.
Seed weight: Mean population seed weight ranges from 1.1–1.7 mg.
Dormancy and germination: Most seeds are dormant when dispersed from the mother plant and several months are required before they will germinate. Germination of mature seeds collected in fall will only occur under a restricted range of temperatures (68/41°F day/night alternation is optimal), whereas in April, seeds will germinate well under a wide range of fluctuating temperature combinations ranging from 28–86°F. Seeds can germinate, however, at daytime temperatures as low as 36°F with nighttime temperatures below freezing. Winter chilling is not required for after-ripening. In a field study, germination peaked when soil temperatures were 59–77°F during the day and 32–41°F at night. In a lab study, germination was best at day/night temperatures of 86/68°F or 95/77°F. Fluctuating temperatures appear to promote germination, but the species is relatively unaffected by light. Germination of Russian-thistle is not limited by dry soil conditions that would inhibit germination of other species. Germination can occur at high salt concentrations only at higher temperatures (higher than 68°F), but germination of seeds removed from salt conditions is best at lower temperatures (59/41°F). This germination response is adapted to western desert conditions, whereby evaporation and saline conditions increase as seasonal temperatures increase, but intermittent dilution of salt in the soil and cooler temperatures are associated with rainfall. These traits coupled with a capacity to germinate very rapidly (in minutes to hours) allow Russian-thistle to establish in environments where favorable conditions are highly transitory.
Seed longevity: Although a few seeds may remain viable deep in the soil for many years, most seeds remain viable for no more than one to two years. In a Nebraska experiment, seeds did not survive for one year. In a Saskatchewan experiment in which seeds were sown on cultivated soil in the fall, 31% emerged the next spring, less than 0.5% emerged the second year and only two individuals (0.04%) emerged the third year.
Season of emergence: Seedlings mostly emerge in early spring, with emergence continuing through late spring. Russian-thistle also can emerge intermittently following light rainfall.
Emergence depth: Seedlings emerge best from seeds located within the surface 0.4–1 inch of soil. A few seedlings can emerge from 2.4 inches but none from 3.2 inches. Emergence from seeds on the soil surface is low unless crop residue is present and/or the relative humidity of the atmosphere is very high.
Photosynthetic pathway: C4
Sensitivity to frost: Russian-thistle, both as a seedling and as a mature plant, is killed by hard frost.
Drought tolerance: Established Russian-thistle plants are extremely drought tolerant and highly water efficient. The root system is at least five times as long as shoots and can extend 5 feet laterally and 6 feet vertically, which partially explains the rapid access to and depletion of soil water by this species.
Mycorrhiza: Russian-thistle does not form mycorrhizal associations. Some evidence indicates that growth can be reduced by mycorrhizal fungi.
Response to fertility: Compared with most crops and other weed species, Russian-thistle growth is not responsive to nitrogen. The species is very good at taking up N when it is in short supply, however, and it concentrates high levels of nitrates (more than 5% N) in shoots under high fertility conditions, a capacity that can enhance its competitiveness with other N-requiring plants. Russian-thistle is also remarkably unresponsive to P.
Soil physical requirements: Russian-thistle occurs primarily on dry, sandy soils. It is also common on loam and silty alkaline soils in prairie regions, but it is uncommon on clay soils. It tolerates and thrives on saline soils that inhibit most plant species. It rarely occurs in wet areas. Seedling emergence is poor on compacted soil.
Response to shade: The species does not tolerate shade.
Sensitivity to disturbance: Small plants cut just above the seed leaves do not survive, which indicates that early season mowing may control the species. Older plants recover from mowing by developing prostrate stems below the cutting level, requiring additional mowing or other control measures. After stems are cut during small grain harvest, the root system regrows at a rate faster than the shoots. Overall regrowth, if left unchecked after harvest, can lead to substantial seed production by fall.
Time from emergence to reproduction: Flowering begins in mid-June and can continue until frost. Seed production occurs from August through fall.
Pollination: Russian-thistle is wind pollinated and can self-pollinate.
Reproduction: Estimates of seed production vary greatly from 2,000 to over 100,000 seeds per plant. Very large plants have been reported to produce up to 150,000 seeds, but plants growing in competition with crops typically produce 5,000–17,000 seeds.
Dispersal: Russian-thistle grows in a ball-like shoot structure that frequently breaks off at the base after senescence and rolls in the wind, dropping seeds as it bounces along. Winds with gusts up to 61 mph are required to break off stems of recently senesced plants. Plants tumble an average distance of 2,100 yards and a maximum distance of 2.5 miles until stopped by fence-lines, roadways or other obstacles. Tumbleweeds caught on railroad cars can spread seeds across the landscape for long distances. Plants retain 26–51% of seeds after tumbling approximately one mile, ensuring seed dispersal over large distances. Seeds also can be spread in waterways and contaminated crop seed or straw. Seeds present in the Columbia River and irrigation water laterals had a 56% germination potential.
Common natural enemies: The native caterpillars Coleophora parthenica and C. klimeschiella are sufficiently destructive to Russian-thistle that they have been released in Canada as biological control agents. Coleophora parthenica also was introduced into the Coachella Valley of southern California, but although the larvae infested most Russian-thistle plants, it had little effect on growth or population levels of this species. The rust fungus Uromyces salsolae, the anthracnose fungus Colletotrichum gloeosporioides and the bare spot fungus Rhizoctonia solani have shown potential to suppress growth under controlled conditions.
Palatability: While young and before spines form, Russian-thistle can provide a good source of forage for livestock and native animals. Oxalates and nitrates in the tissue of Russian-thistle can poison sheep. Nitrates become a problem when the plant is growing on well fertilized soils. Salinity enhances forage quality of Russian-thistle, reduces nitrate and oxalate concentrations at full flower, and creates good forage potential on arid lands.
Note: Russian-thistle pollen is an important contributor to summer hay fever problems in regions where it is common.
Weed Characteristics Summary Table
|Growth habit||Seed weight (mg)||Seed dormancy at shedding||Factors breaking dormancy||Optimum temperature for germination (F)||Seed mortality in untilled soil (%/year)||Seed mortality in tilled soil (%/year)||Typical emergence season||Optimum emergence depth (inches)|
|medium, branched||1.1–1.7||Yes||at||59/32 to 77/41||99||na||early spring||0.4–1|
|Photosynthesis type||Frost tolerance||Drought tolerance||Mycorrhiza||Response to nutrients||Emergence to flowering (weeks)||Flowering to viable seed (weeks)||Pollination||Typical & high seed production (seeds per plant)|
|C4||low||very high||no||low||10||–||both||15,000 & 150,000|
General: The designation “–” signifies that data is not available or the category is not applicable.
Growth habit: A two-word description; the first word indicates relative height (tall, medium, short, prostrate) and second word indicates degree of branching (erect, branching, vining).
Seed weight: Range of reported values in units of “mg per seed.”
Seed dormancy at shedding: “Yes” if most seeds are dormant when shed, “Variable” if dormancy is highly variable, “No” if most seeds are not dormant.
Factors breaking dormancy: The principle factors that are reported to break dormancy and facilitate germination. The order of listing does not imply order of importance. Abbreviations are:
scd = seed coat deterioration
cms = a period subjected to cold, moist soil conditions
wst = warm soil temperatures
li = light
at = alternating day-night temperatures
ni = nitrates
Optimum temperature range for germination: Temperature (Fahrenheit) range that provides for optimum germination of non-dormant seeds. Germination at lower percentages can occur outside of this range. The dash refers to temperature range, and the slash refers to alternating day/night temperature amplitudes.
Seed mortality in untilled soil: Range of mortality estimates (percentage of seed mortality in one year) for buried seeds in untilled soil. Values were chosen where possible for seeds placed at depths below the emergence depth for the species and left undisturbed until assessment. Mortality primarily represents seed deterioration in soil.
Seed mortality in tilled soil: Range of mortality estimates (percentage of seed mortality in one year) for seeds in tilled soil. Values were chosen for seeds placed within the tillage depth and subjected to at least annual tillage events. Seed losses are the result of dormancy-breaking cues induced by tillage, germination and deterioration of un-germinated seeds.
Typical emergence season: Time of year when most emergence occurs in the typical regions of occurrence for each weed. Some emergence may occur outside of this range.
Optimum emergence depth: Soil depths (in inches below the soil surface) from which most seedlings emerge. Lower rates of emergence usually will occur at depths just above or just below this range.
Photosynthesis type: Codes “C3” or “C4” refer to the metabolic pathway for fixing carbon dioxide during photosynthesis. Generally, C3 plants function better in cooler seasons or environments and C4 plants function better in warmer seasons or environments.
Frost tolerance: Relative tolerance of plants to freezing temperatures (high, moderate, low).
Drought tolerance: Relative tolerance of plants to drought (high, moderate, low).
Mycorrhiza: Presence of mycorrhizal fungi. “Yes” if present; “no” if documented not to be present, “unclear” if there are reports of both presence and absence; “variable” if the weed can function either with or without, depending on the soil environment.
Response to nutrients: Relative plant growth response to the nutrient content of soil, primarily N, P, K (high, moderate, low).
Emergence to flowering: Length of time (weeks) after emergence for plants to begin flowering given typical emergence in the region of occurrence. For species emerging in fall, “emergence to flowering” means time from resumption of growth in spring to first flowering.
Flowering to viable seed: Length of time (weeks) after flowering for seeds to become viable.
Pollination: “Self” refers to species that exclusively self-pollinate, “cross” refers to species that exclusively cross-pollinate, “self, can cross” refer to species that primarily self-pollinate, but also cross-pollinate at a low rate, and “both” refers to species that both self-pollinate and cross-pollinate at relatively similar rates.
Typical and high seed production potential: The first value is seed production (seeds per plant) under typical conditions with crop and weed competition. The second value, high seed production, refers to conditions of low density without crop competition. Numbers are rounded off to a magnitude that is representative of often highly variable reported values.
Get More Research and Updated Information on this Weed Species
Beckie, H.J. and A. Francis. 2009. The biology of Canadian weeds. 65. Salsola tragus L. (updated). Canadian Journal of Plant Science 89:7 75–789.
Blackshaw, R.E., J.R. Moyer, R.C. Doram and A.L. Boswell. 2001. Yellow sweetclover, green manure, and its residues effectively suppress weeds during fallow. Weed Science 49: 406–413.
Crompton, C.W. and I.J. Bassett. 1985. The biology of Canadian weeds. 65. Salsola pestifer A. Nels. Canadian Journal of Plant Science 65: 379–388.
Schillinger, W.F. 2007. Ecology and control of Russian-thistle (Salsola iberica) after spring wheat harvest. Weed Science 55: 381–385.
Young, F.L. 1986. Russian-thistle (Salsola iberica) growth and development in wheat (Triticum aestivum). Weed Science 34: 901–905.