California Pest Rating
Dittrichia viscosa (L.) Greuter: false yellowhead
Former Pest Rating: Q
CURRENT Pest Rating: A | Proposed Seed Rating: P
False yellowhead (Dittrichia viscosa) has been rated as “Q” on the CDFA Plant Pest Rating since 2014. This plant is on the “Alert list” for Environmental weeds in Australia. Recent reports of its presence in Solano County has prompted issuance of a permanent rating.
History & Status:
False yellowhead (Dittrichia viscosa) is an erect, perennial, soft-wooded shrub, 1–1.5 m tall and 1 m wide. Its leaves are greyish-green, partially clasping and elliptical. The yellow flowers are daisy-like and 10–20 mm across, with radiating petal-like flowers. The flowers are surrounded by narrow, triangular, sticky bracts. The seeds are approximately 2 mm long, with about 15–25 bristles at the base (Ratcliffe, 1976). The roots can be quite substantial, even in small plants. The young stems and leaves are covered with glandular hairs which exude a sticky foul-smelling oil. The oil can cause allergic reactions. It is native to Northern Africa, the Middle East, India, and southern Europe (Brullo & de Marco, 2000), but it has expanded its range in response to human disturbance and proved tolerant of harsh water and mineral stress (Wacquant, 1990; Thompson, 2005; Murciego et al. 2007). False yellowhead inhabits disturbed places, roadsides, pastures, fields, riparian woodlands, levees, washes, and margins of tidal marshes. (Blanco 2011; Wacquant, 1990). False yellowhead was first found in California in 2014 (Consortium of California Herbaria). False yellowhead’s ecology seems to be similar to its close relative stinkwort (D. graveolens), a serious weed in California (Ditomaso & Brownsey, 2013; Wacquant, 1990).
Official Control: False yellowhead has not been listed as a harmful organism (Phytosanitary export database- USDA Phytosanitary Certificate issuance and Tracking system (PExD). The Solano County Agricultural Commissioner’s staff has been controlling and monitoring this plant since it was first found.
California Distribution: Known only from Solano County in California (Consortium of California Herbaria).
California Interceptions: It has been found growing along McGary Road in Solano County, as reported multiple times by the county agricultural commissioner’s office. (Pest and Damage Report Database). It has not yet been intercepted at CA borders.
United States: False yellowhead was collected in three states in the eastern U.S. (USDA Plants), but it is unlikely that it persisted beyond the late1800s. (FNA, 1993+).
International: False yellowhead is common throughout the Mediterranean. Its native range includes the coasts of southern Europe (including France, Spain, Greece, Italy, Bulgaria and Turkey), the Middle East (Israel, Jordan and Syria), as well as northern Africa (Algeria, Egypt and Libya) (Ratcliffe, 1976; Brullo & de Marco, 2000). It is spreading rapidly in Southeastern and Southwestern Australia (Baldwin et al., 2012).
The risk False yellowhead would pose to California is evaluated below:
Consequences of Introduction:
1) Climate/Host Interaction: False yellowhead is a ruderal plant species adapted to areas disturbed and altered by human activity (Wacquant, 1990). The typical habitats of viscosa include arroyos, abandoned agricultural fields, roadsides, trails, and disturbed urban sites (Ratcliffe, 1976). It occurs on various soil types and is tolerant of high mineral soils (Wacquant, 1990). Although it is drought tolerant, it prefers the margins of wetlands (Warlop et al., 2010). Once established after disturbance, it can spread to less disturbed situations (Wurcquart, 1990). Therefore, false yellowhead receives a High (3) in this category.
Evaluate if the pest would have suitable hosts and climate to establish in California:
– 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:
– 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: False yellowhead spreads via seed. Seed dispersal is aided by an arrangement of bristles at the end of the seed (pappus) that catches the wind. (Australian Weed Management Guide). It produces prolific seed that secretes a sticky exudate causing seed to cling to clothing, animal fur and machinery. The seed bank of its close relative Stinkwort is moderately persistent (Cal-IPC). False yellowhead receives a High (3) in this category.
Evaluate the natural and artificial dispersal potential of the pest:
– 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: False yellowhead can lower range productivity. It is unpalatable to livestock (Philbey and Morton, 2000). Furthermore, because of the barbs on the pappus of the seeds, it leads to enteritis and other gastrointestinal disease in livestock. As they are similar to those of Stinkwort, false yellow head is likely to have similar impacts on livestock. It is thought that false yellowhead would have similar impacts on grazing animals. Thirty years after introduction to South Australia, false yellowhead is a bad weeds of roadsides. Some people are allergic and develop severe dermatitis after contacting false yellowhead plants (Máñez et al., 1999; Hernández et al., 2001). It is also allelopathic to other plants and suppresses seed germination (Omezzine et al., 2011). False yellowhead receives a Medium (2) in this category.
Evaluate the economic impact of the pest to California using the criteria below:
Economic Impact: D, F
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.
Economic Impact Score: 2
– 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: False yellowhead is likely to trigger new chemical treatments by ranchers and land managers. The plant can dominate roadsides, disturbed grassland, and wetland margins, excluding native plants and lowering biodiversity (Australia Weed Management Guide). Rare taxa that might be affected in CA include grassland species such as showy Indian clover (Trifolium amoenum) and CA filaree (California macrophylla), and vernal pool species such as Burke’s goldfields (Lasthenia burkei) and CA tiger salamander (Ambystoma californiense). The plant can disrupt natural communities and exclude cultural plants from a landscape. False yellowhead receives a High (3) in this category.
Evaluate the environmental impact of the pest on California using the criteria below:
Environmental Impact: A, C, D
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:
Environmental Impact Score: 3
– 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 False yellowhead: High (14)
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: False yellowhead has been found in one county in California. 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: High (13)
Uncertainty is low, as the plant has spread widely in the Mediterranean and South Australia. It also shows signs of fast establishment in its one known occurrence in California.
Conclusion and Rating Justification:
An A rating is recommended, as the plant is invasive, but not yet widespread. There is still the chance to eradicate this plant from North America.
Australian Weed Management Guide. False yellowhead. Accessed 10/11/2016:
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.
Blanco G. 2011. Dittrichia in Claves de la Flora Vascular de Andalucía Oriental. G. Blanca, B. Cabezudo, M. Cueto, C. Morales Torres & C. Salazar, eds. Servicio de Publicaciones de las Universidades de Almería, Granada, Jaén y Málaga. Universidad de Granada. Granada, Spain.
Brullo, S & de Marco, G. 2000. Taxonomical revision of the genus Dittrichia (Asteraceae), Portugaliae Acta Biol. 19: 341–354.
Consortium of California Herbaria. Accessed 10/11/2016: ucjeps.berkeley.edu/consortium/
Flora of North America Editorial Committee, eds (FNA). 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford.
Hernández, V., R. M. del Carmen, S. Máñez, J. M. Prieto, R. M. Giner, & J. L. Ríos. 2001. A mechanistic approach to the in vivo anti-inflammatory activity of sesquiterpenoid compounds isolated from Inula viscosa. Planta Medica 67: 726-731.Máñez, S., M. C. Recio, I. Gil, C. Gómez, R. M. Giner, P. G. Waterman & J. L. Ríos 1999. A glycosyl analogue of diacylglycerol and other antiinflammatory constituents from Inula viscosa. Journal of Natural Products 62: 601-604.
Murciego, A. M., A. G. Sánchez, M. A. R. González, E. P. Gil, C. T. Gordillo, J. C. Fernández & T. B. Triguero 2007. Antimony distribution and mobility in topsoils and plants (Cytisus striatus, Cistus ladanifer and Dittrichia viscosa) from polluted Sb-mining areas in Extremadura (Spain). Environmental Pollution 145: 15-21.
Omezzine, F., A. Rinez, A. Ladhari, M. Farooq & R. Haouala. 2011. Allelopathic potential of Inula viscosa against crops and weeds. International Journal of Agriculture and Biology 13: 841-849.
Parolin P, M Ion Scotta, & C Bresch. 2014. Biología de Dittrichia viscosa, una planta ruderal del Mediterráneo. Phyton (Buenos Aires) vol.83.
Philbey A. & A.G. Morton 2000. Pyrogranulomatous enteritis in sheep due to penetrating seed head of Dittrichia graveolens. Australian Veterinary Journal 78: 858-860
Pest and Damage Record Database, Plant Health and Pest Prevention Services, CA Department of Food and Agriculture. Assessed Date: 10/18/2016
Phytosanitary Export Database- USDA Phytosanitary Certificate issuance and Tracking system (PExD), Date Assessed: 10/18/2016. https://pcit.aphis.usda.gov/PExD/faces/PExDReport.jsp
Ratcliffe, D. 1976. Dittrichia in Flora Europaea Vol. 4: Plantaginaceae to Compositae. T. G. Tutin, V. H. Heywood, N. A. Burges, D. H. Valentine, S. M. Walters, & D. A. Webb, eds. Cambridge University Press. United Kingdom.
Sinden J., R. Jones, S. Hester, D. Odom, C. Kalisch & R. James (2004). The economic impact of weeds in Australia. Report to the CRC for Australian Weed Management. Pp. 1-65.
Thompson, J. D. 2005. Plant Evolution in the Mediterranean. Oxford University Press, Oxford.
USDA Plants; Dittrichia viscosa. Accessed 10/11/2016: http://plants.usda.gov/core/profile?symbol=DIVI6
Wacquant, J. P. 1990. Biogeographical and physiological aspects of the invasion by Dittrichia (ex-Inula) viscosa W. Greuter, a ruderal species in the Mediterranean Basin. Pp. 353-364 in Biological Invasions in Europe and the Mediterranean Basin. F. di Castri, A.J. Hansen, and M. Debussche, eds. Springer Netherlands, Dordrecht.
Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6650; plant.health[@]cdfa.ca.gov
Comment Period: CLOSED
45-day comment period: Dec 1, 2016 – Jan 15, 2017
Pest Rating: A | Proposed Seed Rating: P