Parthenium hysterophorus L. | Santa Maria feverfew
California Pest Rating for
Family: Asteraceae
Parthenium hysterophorus L. – Santa Maria feverfew
Pest Rating: A |  Seed Rating: P

Initiating Event:

This plant has been rated as “Q” on the CDFA Plant Pest Rating List after a find in a greenhouse growing in coir from Sri Lanka. There have been two detections of this plant in Orange County in 2016.


Parthenium lobatum Buckley

History & Status:

Santa Maria feverfew is an aggressive, annual, herbaceous weed of highly negative economic importance. This erect, ephemeral herb is known for its vigorous growth and high fecundity, especially in warmer climates. It is native to the southern United States, Mexico, Central and South America; however the native range north of Mexico is not clear. Santa Maria feverfew is a prolific weed belonging to the daisy family (Asteraceae), producing thousands of small flower heads each yielding several single-seeded fruits on reaching maturity. Within the past century it has found its way to Africa, Australia, Asia and many Pacific Islands. It has now become one of the world’s seven most serious weeds in warm climates. It is found on abandoned lands, residential areas, railway tracks, road right-of-ways, drainage and irrigation canals, lawn edges, and other disturbed areas. It has wide adaptability, drought tolerance, high seed production ability and a long-lived soil seed bank. This weed invades established gardens, plantations and vegetable crops. Due to its high fecundity, a single plant can produce 10,000 to 15,000 viable seeds in one year and the fruits can disperse and germinate to cover large areas.

Official Control: Santa Maria feverfew is recognized as invasive weed in certain countries of Asia, Africa and Oceania. In 2014, it was added to the California list of noxious weeds (CCR Section 4500).

Much research has been carried out in South Asia on the control of this plant, including biological control. It has not yet established in California and no work has been done here.

California Distribution: One population was found on the U.C. Campus in Riverside in 1981. This population is evidently gone (Andrew Sanders, pers. comm.). Populations of Santa Maria feverfew have been found growing in two areas of California recently in Orange County (in 2016) and it has not yet naturalized in California.

California Interceptions:  Santa Maria feverfew has not been intercepted at California borders.

United States Distribution: Santa Maria feverfew has a native range in in the subtropical regions of North and South America and has been found in many Eastern states. It is now well established in the Southern United States

International Range: Santa Maria feverfew is native to Mexico, Central and South America. It is distributed in parts of Asia, Africa, North America, the Caribbean, Europe and Oceania.

This risk Santa Maria feverfew would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Santa Maria feverfew is a weed of semi-arid subtropical, tropical and warmer temperate regions. It is often found in riparian zones. It is able to invade natural ecosystems and has the ability to cause habitat changes in native grasslands and open woodlands. The climate in inland regions of California is more continental with some semi-arid areas. The Central Valley has hotter summers with a mediterranean style climate. This weed is likely to establish in small areas of California. Score: 2

Evaluate if the pest would have suitable hosts and climate to establish in California.  Score: 2

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

Evaluate the host range of the pest.

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: Risk is High (3). The plant produces via numerous seeds that are able to spread rather quickly. Santa Maria feverfew can be dispersed through water, farm machinery, industrial machinery, feral animals, humans, vehicles, stock fodder, and movement of stock, grain and seed (PAG 2000). It can also be spread by wind due to its small and light seed size (Navie et al., 1996; Taye, 2002). Score: 3

Evaluate the natural and artificial dispersal potential of the pest. Score: 3

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: Risk is high (3) as the plant can lower range productivity and land value. Santa Maria feverfew has been known to impact pastoral regions and can replace forage plants. This weed is considered to be a cause of allergic respiratory problems, contact dermatitis, and mutagenicity in human and livestock. Crop production is drastically reduced in infested fields owing to its ability to suppress growth of other plants (allelopathy). Santa Maria feverfew can also impact crop production indirectly by serving as an alternate hosts for other plant pests and disease causing organisms. It is estimated that in heavily infested crops, the cultivation costs may be doubled because the prepared ground must be re-worked to eliminate the emergent parthenium weed seedlings (Chippendale and Penetta). Score: 3

Evaluate the likely economic impacts of the pest to California using the criteria below. Score: 3

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.

Score the pest for Environmental Impact:

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: Risk is high (3) as the plant can disrupt natural communities and cultural plants in a landscape. It can cause prolonged toxic effects on the soil environment. The invasive ability and its allelopathy have given Santa Maria feverfew the ability to disrupt ecosystems by replacing dominant flora and suppressing natural vegetation, thereby becoming a threat to biodiversity. Sparse vegetation is seen in infested areas. Santa Maria feverfew has an adverse effect on native plants. It has been reported to cause irreversible habitat change in native Australian grasslands, open woodlands, river banks and flood plains. Santa Maria feverfew rapidly invade new surroundings and often replaces indigenous species. Score: 3

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:

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 Santa Maria feverfew:

Add up the total score and include it here. (14)

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: 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. Score: -1

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. Final score: 13


The extent of suitable habitat in CA is not clear, but this plant has shown itself to be capable of wide invasion where warmth and some summer water are available.

Conclusion and Rating Justification:

A very bad weed. Despite its limited adaptability to California, it deserves an A rating, as it is so harmful and as it has invaded similar habitats in Australia.


Adkins, S.W. and S.C. Navie. 2006. Parthenium weed: a potential major weed for agro-ecosystems in Pakistan. Pak. J. Weed Sci. Res. 12: 19-36.

Consortium of California Herbaria (

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

Lakshmi C. & C. R. Srinivas. 2007. Parthenium: A wide angle view. Indian J. Dermatol Venereol Leprol. 73:296–306.

Patel, S. 2011. Harmful and beneficial aspects of Parthenium hysterophorus: an update. 3 Biotech. 1: 1–9.

National Plant Germplasm System: GRIN database: USDA APHIS

Weeds of the United States and Canada: Southern Weed Science Society (USDA Natural Resource Conservation)

Invasive Species Compendium: Parthenium hysterophorus

PAG, 2000. Parthenium weed. Parthenium Action Group Information Document. CSIRO, Australia.

Navie SC, McFadyen RE, Panetta FD, Adkins SW, 1996. The biology of Australian weeds. 27. Parthenium hysterophorus L. Plant Protection Quarterly, 11(2):76-88; 4 pp. of ref.

Taye T, 2002. Investigation of pathogens for biological control of parthenium (Parthenium hysterophorus L) in Ethiopia. PhD Thesis. Humboldt University of Berlin, Germany.

Chippendale JF, Panetta FD, 1994. The cost of parthenium weed to the Queensland cattle industry. Plant Protection Quarterly, 9(2):73-76; 14 ref.

Distribution of Santa Maria feverfew in 1994 (Adkins and Navie, 2006)
Distribution of Santa Maria feverfew in 1994 (Adkins and Navie, 2006)

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0317;[@]

Pest Rating: A |  Proposed Seed Rating: P

Posted by ls 

One thought on “Parthenium hysterophorus L. | Santa Maria feverfew”

  1. As invasive plant co-chair for Orange County CNPS we agree with this proposal.
    I was involved in the detection of the two recent occurrences, both in OC. The published research seems to conclude that this is a weed species with a high potential for ecological disruption as an invasive plant as well as having a potentially significant economic impact on grazing systems and agricultural lands in CA.
    The species is under a similar review with the California Invasive Plant Council. Some research indicates that this species may have high phenotypic plasticity, making it, over time, highly adaptable to new ecological niches, such is we have in CA. In addition, its ecological amplitude and intensity in CA would appear to be high. Being an annual weed, with high seed production, high viability of seed, wind dispersion of the seed and the ability to disperse via other anthropogenic means would lead to a high invasive potential in California.
    This is a very bad weed. We support this proposal.

    Ron Vanderhoff
    Orange Co. CA Native Plant Society

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