Orange Hawkweed | Hieracium aurantiacum

Orange Hawkweed, photo by Becca MacDonald, Sault College,
California Pest Rating for
Hieracium aurantiacum:  Orange hawkweed
Family : Asteraceae
Pest Rating : B |  Proposed Seed Rating: P

Initiating Event:

Orange hawkweed had no previous pest rating, it has been reported in Nevada, Siskiyou, and Mono counties. A pest rating proposal is required to determine a permanent rating for this pest.

History & Status:

Background: Orange hawkweed is a fibrous rooted perennial herb in the Aster family (Asteraceae) that grows 10-36 inches tall. It blooms in late spring to early summer and  produces bright orange to orange-red ray flowers with 5 to 30 flower heads. Flower heads close every evening and reopen at mid-morning each day prior to seeding. Every flower head can produce between 12 and 50 small brown or black single seeded fruit  and has a hairy tuff at one end that allows the seed to be carried by the wind. Flower stems are bare, all plant parts contain a milky juice and leaves are covered with stiff hairs. Orange hawkweed, like all invasive hawkweeds, has a shallow and fibrous root system and underground creeping rhizomes.The plant rosettes also originate from aboveground stolons (resembling those of strawberry). The stolons are capable of producing new plants where the runners contact soil; therefore, patch expansion is accomplished primarily by stolon growth and/or rhizomes. Long distance spread is mostly by wind and water borne seed or by seeds carried in and on wildlife and livestock2,3.

The scientific name Hieracium is of Greek origin and means ‘hawk’. Hawkweed refers to the fact that many species of this genus grow at high altitudes that are only accessible by hawks. It spread rapidly in North America after its introduction as an ornamental and/or as a contamination of pasture seeds from its native range in Europe1.

Worldwide Distribution: Orange hawkweed is native to Europe it grows; in subalpine areas resulting in a disjunct distribution1. It has spread to most of Europe and in southern Russia. Due to its use as a garden ornamental and rock garden plant,  it was introduced into exotic locations including New Zealand, Tasmania, Japan, Canada, Australia and North America1,3.

Official Control: Orange hawkweed is listed as a harmful organism in Korea5. It is   prohibited entry to Australia, New Zealand and the USA. Orange hawkweed is deemed a noxious weed in Oregon, Washington, Idaho, Montana and British Columbia. This makes it unlawful to transport, propagate and sell in these localities3.

California Distribution: Orange hawkweed has been reported  from Siskiyou, Nevada and Mono counties.

California Interceptions: One PDR (470P06027609 from Siskiyou County) was reported in the Pest and Damage Record Database by CDFA4. There are five vouchers from Siskiyou , Nevada and Mono  counties documented  between 1967 and 2013. Only the Siskiyou County population seemed  adventive.

The risk Hieracium aurantiacum (Orange hawkweed) would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Orange hawkweed is well established in Oregon and Washington, and is spreading there. These states have similar habitat to northern California. Therefore, there is a high risk that it will establish in this part of California. It receives a Medium (2) 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) Pest Host Range: Orange hawkweed does not require any one host, but grows wherever ecological conditions are favorable. It receives a High(3) in this category.

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: Orange hawkweed reproduces and spreads through prolific seed production, as well as vegetatively through stolons, and rhizomes. Under ideal conditions, one plant can spread and infest an area two to three feet in diameter in its first year of growth. Seeds can be dispersed by wind, water, or “hitch-hiking” and are often moved in contaminated soil associated with transplanting new plants into gardens and flowerbeds2. Seeds are able to germinate immediately after dropping from the plant and can remain viable in the soil for up to seven years3. It receives a High (3) in this category.

Evaluate the 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: Orange hawkweed is invasive in natural or lawn environments in high latitude and altitude areas. It can form mats that prevent the growth of forest understory plants. Orange hawkweed monocultures may degrade forest rangeland, reducing the amount of forage available to livestock3. It receives a Low (1) in this category.

Evaluate the economic impact of the pest to California using these criteria.

Economic Impact: D

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: (1)

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: Orange hawkweed is an aggressive competitor for space, light, and soil nutrients. It has been reported to be allelopathic, producing phytotoxic chemicals in pollen grains that inhibit seed germination, seedling emergence and regeneration of other plants2.  Rare taxa that might be affected include species such as Kincaid’s lupine (Lupinus sulphureus ssp. kincaidii),Fender’s Blue Butterfly (Plebejus icarioides ssp. fendri) and Humboldt milk–vetch (Astragalus agnicidus).

It receives a High(3) in this category.

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

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. Significantly impacting, home/urban gardening or ornamental plantings.

Environmental Impact Score: (3) cultural practices

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 Orange hawkweed: 

Rating (Score): Add up the total score and include it here

Low = 5-8 points

 Medium = 9-12 points

High = 13-15 points

Total points based on above criteria, which does not take into account the current  distribution in California: Medium (12).

6) Post Entry Distribution and Survey Information: Orange hawkweed has been reported in Mono, Siskiyou and Nevada  counties and may be eridicate at this time. 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.

Final Score:

The final score is based on introduction score minus the post entry distribution and survey information Score: (11)


Orange hawkweed has been present in California about 30 years and it is localized in a limited area. It has the potential to spread to more acreage and may be eradicated at this time. It is likely that this plant will come to dominate many new areas and increase its density and distribution.

Conclusion and Rating Justification:

Conclusions of the harm associated with this pest to California using all of the evidence presented above: Based on the score listed above, Orange hawkweed is a Medium risk. Although it is only medium risk in California, it is possible to keep it out of the State with modest effort. Given this, and its ability to spread widely and displace native plants, a “B” rating is proposed.

  1. Ghislaine Cortat   CABI online Orange hawkweed. Accessed 4-25-17.
  2. Oregon Department of Agriculture Plant Pest Risk Assessment for Orange hawkweed, Hieracium aurantiacum  Accessed  4-25-2017.
  3. US Forest Services Fact Sheet.  Accessed  4-25-2017.
  4. Pest and Damage Record Database, California Department of Food and Agriculture, Plant Health and Pest Prevention Services. Accessed 4-25-2017
  5. USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD). Accessed 4-25-2017.

Responsible Party:

Javaid Iqbal, California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6695;[@]


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Pest Rating : B |  Proposed Seed Rating: P

Posted by ls