California Pest Rating for
Chrysanthemoides monilifera: Bitou bush
Pest Rating: A | Proposed Seed Rating: R
PEST RATING PROFILE
This plant has been recently discovered spreading from a single population in Orange County.
History & Status:
Background: Bitou bush is a small shrub (to 2 meters) native the Cape Region of South Africa. It is a semi-succulent plant with ascending candelabra-like branches and elliptical leaves without a petiole about 80 mm long. The flowers heads are borne in summer through fall. The ray flowers and disk flowers are bright yellow. Although it most likely arrived in CA as a garden plant, it is no longer available in the trade (except rarely as seed). Its distribution is limited by cold, as it is intolerant of frost.
Official Control: Bitou bush has not been subject to official control.
California Distribution: Known from 3 historic populations in Orange and San Diego Counties. These most likely are or were persisting from cultivation.
California Interceptions: None.
United States: Bitou bush has been reported from California only.
International: Bitou bush is native to South Africa. It is reported as naturalized and as an environmental weed in Australia and New Zealand where millions of dollars have been spent on control efforts.
This risk Bitou bush would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: The plant has had at least 3 introductions in CA. One of these populations is beginning to spread. It is very invasive in eastern Australia in areas with a similar climate to parts of California. Therefore Bitou bush 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: Bitou bush produces via numerous achenes (“seeds”) that are enclosed in a fleshy fruit dispersed by birds. Bird dispersal is an efficient means of plants establishing new populations. The seed bank is moderately persistent. Known populations have not spread until recently. Bitou bush receives a Medium (2) 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: Bitou bush does not persist well in grazed areas due to browsing and trampling. Bitou bush receives a Low (1) 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).
D. The pest could negatively change normal 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: Chrysanthemoides monilifera out competes native vegetation in coastal environments in Australia and New Zealand, and invasion can lead to a decline in both floral and faunal diversity, changing ecosystem composition. It changes ecosystem processes by altering nutrient cycling, particularly nitrogen cycling, at the expense of native species and creating heavy shade in normally high light areas. It is considered a “weed of national significance” in Australia and has replaced entire stands of native species. This species is tolerant of saline conditions near coastal areas. In addition, it can create a favorable environment for other invasive weeds. Rare taxa that might be affected include strand species such as Laguna Beach dudleya (Dudleya stolonifera) and sagebrush scrub species such as California gnatcatcher (Polioptila californica). Because it forms dense patches, it could interfere with recreation along the coast and invade expensive coastal properties requiring control. Bitou bush 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. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.
Score the pest for Environmental Impact. Score:
– 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 Bitou bush: Medium (12)
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: Bitou bush is very local in CA. It receives a Low (-1) 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.
The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (11)
As Bitou bush has invaded Australia and is beginning to spread in CA, uncertainty is low.
Conclusion and Rating Justification:
A potentially bad weed in CA. Bitou bush merits an “A” rating to prevent its further spread in California. It has a low risk as a potential seed contaminant, so it should be restricted in seed for planting.
Adamson, R. S. & T. M. Salter 1950. Flora of the Cape Peninsula. Juta & Co. Cape Town.
Baldwin, B. G., D. H. Goldman, D. J. Keil, R. Patterson, T. J. Rosatti, & D. H. Wilken, editors. 2012. The Jepson manual: vascular plants of California, second edition. University of California Press, Berkeley.
Bond, P. & P. Goldblatt 1984. Plants of the Cape Flora: A descriptive catalogue. National Botanic Gardens of South Africa, Kirstenbosch.
Consortium of California Herbaria accessed 1/21/2015: ucjeps.berkeley.edu/consortium/
Coutts-Smith, A. J., & P. O. Downey. 2006. Impact of weeds on threatened biodiversity in NSW. CRC for Australian Weed Management, Adelaide, Australia.
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford.
Grice, A. C., S. Campbell, R. Breaden, F. Bebawi, & W. Vogler. 2008. Habitat management guide-Rangelands: Ecological principles for the strategic management of weeds in rangeland habitats. CRC for Australian Weed Management, Adelaide, Australia.
Lindsay, E. A., & K. French. 2005. Litterfall and nitrogen cycling following invasion by Chrysanthemoides monilifera ssp. rotundata in coastal Australia. Journal of Applied Ecology 42: 556-566.
USDA Weed Risk Assessment of Chrysanthmoides monilifera accessed 1/21/2015: http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/Chrysanthemoides_monilifera_WRA.pdf
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.
Pest Rating: A | Proposed Seed Rating: R
Posted by ls