Hieracium aurantiacum L.
Vectors of spread:
General: Orange Hawkweed is a fast-spreading, hairy perennial plant, that can grow up to 60 cm tall. It is one of 14 non-native hawkweed species in BC.
Flowers: The flowers are bright orange or yellow clusters, and sit atop slender unbranched stems.
Stem: Stems are upright, unbranched, contain a milky sap, and are covered with black, bristly hairs.
Leaves: Leaves are hairy and arranged in a rosette at the base of the plant. Few to no leaves are found on the stem.
- Indian Paintbrush (Castilleja spp.): a native wildflower that can be many colours including orange and red.
Habitat and Origin
Orange Hawkweed was introduced from Europe to North America in 1818, most likely as a garden ornamental and as part of contaminated pasture seeds. This species can be found in subalpine meadows, pastures, clearings, roadsides, and other open and disturbed sites. Orange Hawkweed prefers areas with well-drained, coarse-textured soils.
Propagation and Vectors of Spread
Orange Hawkweed spreads by vegetatively through both above-ground runners called stolons and below-ground roots called rhizomes, as well as by seed.
Seeds are primarily dispersed by wind but are also spread by machinery, footwear, as well as in contaminated soil and garden waste. Orange Hawkweed is also sometimes sold as an ornamental.
Economic and Ecological Impacts
Orange Hawkweed forms dense mats that outcompete native species, leading to a drastic change in vegetation, loss of forage for stock, and loss of biodiversity.
Orange Hawkweed crowds out desirable forage plants and therefore can reduce agricultural productivity, as well as decrease land values.
What Can I Do?
Orange Hawkweed is found throughout the Sea to Sky, so PREVENTION of further spread is key.
Learn to identify Orange Hawkweed: use the images presented in this profile page.
What to do if you spot it: You can report any Orange Hawkweed sighting by clicking here.
Play, Clean, Go. Wash equipment and vehicles at designated cleaning sites before leaving infested areas. Remove any plant material from equipment, vehicles, and clothing.
- Regularly monitor properties for weed infestations.
- Ensure soil and gravel is free of Orange Hawkweed before transporting.
- Ensure plants (particularly flowering heads or root fragments) are bagged or covered to prevent spread during transport to designated disposal sites (e.g. landfill).
- Plant Orange Hawkweed in a garden, no matter how well-contained its enclosure may seem.
- Move soil or gravel that has been contaminated with Orange Hawkweed.
- Compost any flowering heads or plant parts. Instead, make sure to bag these plant parts and dispose of them at the landfill.
- Hand pull or dig when soil is moist.
- Remove all flower heads and buds from the site since they will continue to mature even after the plant is pulled.
- Mechanical control of Orange Hawkweed has had limited success since disturbing the stolons and rhizomes may only help the plant to spread.
- Although mowing prevents seed production by removing flowering stems, repeated mowing encourages faster vegetative spread.
In soils with low nitrogen and sulphur levels, the competitive ability of grasses can be increased through application of fertilizer with nitrogen and sulphur components.
Orange Hawkweed is effectively controlled by dicamba, clopyralid, picloram, and picloram + 2,4-D. However, picloram is not suitable for wet, coastal soils.
Complete eradication is unlikely, so a follow-up with fertilizer and top dressing is required.
We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Application Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.
No biocontrol is available at this time; more research is required.
When the soil is moist, Orange Hawkweed plants can be hand-pulled. Ensure that you remove as much of the root mat as possible. However, mechanical control methods can have limited success since disturbing the stolons and rhizomes may only help the plant to spread. A cultural control method of applying fertilizer with nitrogen and sulphur components may allow grass species to outcompete Orange Hawkweed, but only in soils that have low nitrogen and sulphur concentrations. If any chemical treatment is recommended for the removal of Orange Hawkweed, it must be carried out by a person holding a valid BC Pesticide Applicator certificate.
- E-Flora BC, Hieracium aurantiacum, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Hieracium%20aurantiacum
- Invasive Species Compendium (CABI), Pilosella aurantiaca, https://www.cabi.org/ISC/datasheet/27160
- Invasive Species Council of BC, Field Guide to Noxious Weeds and Invasive Plants of BC, https://bcinvasives.ca/documents/Field_Guide_to_Noxious_Weeds_Final_WEB_09-25-2014.pdf
- Invasive Species Council of BC, Orange Hawkweed, https://bcinvasives.ca/invasive-species/identify/invasive-plants/hawkweeds