Russianthistle or Southern
Russianthistle [Salsola australis R. Br.][SASKR][CDFA list: C] Biocontrol
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
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.
PLANT:Leaves alternate, sessile, linear
to needle-like, gradate into rigid, spine-tipped bracts in the inflorescences.
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
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
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
HABITAT:Typically infests sandy soils on disturbed sites, waste places,
roadsides, cultivated and abandoned fields, disturbed natural and semi-natural
PROPAGATION/PHENOLOGY:Reproduce by seed. Seed appears to require an after-ripening
period. Cotyledons are photosynthetic upon emergence.
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.
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 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.