Salsola tragus L.: Russian-thistle

California Pest Rating for

Salsola tragus L.: Russian-thistle

Caryophyllidae; Chenopodiaceae

Pest Rating: C | Proposed Seed Pest Rating: R

PEST RATING PROFILE

Initiating Event:

This plant has been rated as “C” on the CDFA Plant Pest Rating list and was recently assigned a Q rating by the botany lab.

History & Status:

Russian-thistle is a densely-branched, sub-shrubby annual, to about 1 m tall, with inconspicuous flowers and 5-winged fruits. Fruiting plants die and detach from their roots, forming a “tumbleweed” that tumbles over the ground, dispersing the single-seeded fruits far and wide. Russian-thistle is part of the confusing taxonomic complex that is native to the Old World and Australasia. In the current Jepson Manual, a narrow species interpretation is accepted and our plants are recognized as Salsola tragus. Russian-thistle can act as an alternate host for the virus that causes curly-top in sugarbeets, tomatoes, and melons. Russian-thistle favors disturbed sites, silty dry sites, and saline desert areas; It was introduced into the United States in South Dakota in 1874 as a contaminant of flax seed.

Official Control: Russian-thistle has been a “C” listed noxious weed by California.

California Distribution: Russian-thistle is known from all areas of California except for the North Coast and adjacent mountains.

California Interceptions: Fruits of Russian-thistle are detected commonly in vehicles entering California.

United States: Russian-thistle has been found in all states except Alaska and Florida.

International: Russian-thistle is native to arid, disturbed, and saline areas of Eurasia.

This risk Russian-thistle poses to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: The plant is particularly adapted to hot interior zones but is widespread in many coastal areas as well. Its widespread distribution demonstrates its ability to occupy California. Therefore, Russian-thistle receives a High (3) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Host Range: Risk is High (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

3) Pest Dispersal Potential: Russian-thistle produces via numerous seeds that seem to be able to spread via the tumbleweed habit. Russian-thistle receives a High (3) in this category.

Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Russian-thistle invades cropland, as well as rangeland. It can also serve as a host for curly-top virus. In some instances, detached plants have impeded traffic traversing arid areas. Russian-thistle receives a High (3) in this category.

Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield

B. The pest could lower crop value (includes increasing crop production costs)

C. The pest could trigger the loss of markets (includes quarantines by other states or countries)

D. The pest could negatively change normal production cultural practices

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

–Low (1) causes 0 or 1 of these impacts
–Medium (2) causes 2 of these impacts
–High (3) causes 3 or more of these impacts

5) Environmental Impact: Russian-thistle is likely to trigger new chemical treatments by ranchers and land managers. The plant can dominate subsaline areas or desert washes, excluding native plants and lowering biodiversity. Endangered taxa that might be affected include those that use arid areas such as the brittlescale (Atriplex depressa) and alkali mariposa-lily (Calochortus striatus). It might also reduce habitat value for endangered animals such as the giant kangaroo rat (Dipodomys ingens) by displacing food plants. The effect on local invertebrates is unknown, but the invertebrate fauna associated with Russian-thistle are unlikely to be as diverse as those that associate with native plants that are displaced by Russian-thistle. The plant can disrupt natural communities. Russian-thistle receives a High (3) in this category.

Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. Significantly impacting cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact.

–Low (1) causes none of the above to occur
–Medium (2) causes one of the above to occur
–High (3) causes two or more of the above to occur

Consequences of Introduction to California for Russian-thistle: High (15)

Add up the total score and include it here.

–Low = 5-8 points
–Medium = 9-12 points
–High = 13-15 points

6) Post Entry Distribution and Survey Information: Russian-thistle has been found in in all but 3 counties in California. It receives a High (-3) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

–Not established (0) Pest never detected in California, or known only from incursions.
–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (12)

Uncertainty:

There is little uncertainty, as this is an invasive agricultural and environmental weed in California.

Conclusion and Rating Justification:

A terrible weed because of its ability to grow in arid poorly vegetated regions. Because it has spread throughout most or nearly all of its potential range, it merits a C rating.

References:

Baldwin, B. G., D. H. Goldman, D. J. Keil, R. Patterson, T. J. Rosatti, and D. H. Wilken, editors. 2012. The Jepson manual: vascular plants of California, second edition. University of California Press, Berkeley.

CDFA Encycloweedia; Salsola tragus. Accessed 5/25/2015: http://www.cdfa.ca.gov/plant/ipc/encycloweedia/weedinfo/salsola.htm

Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/).

Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford.

Longland, W. S. 1995. Desert rodents in disturbed shrub communities and their effects on plant recruitment. General Technical Report Intermountain Research Station, USDA Forest Service No. INT-GTR-315: 209-215.

U.S.D.A. Plants database. Salsola tragus. Accessed 5/24/2015: http://plants.usda.gov/core/profile?symbol=SATR12

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312; plant.health[@]cdfa.ca.gov.