May’s Weed of the Month: Orange Hawkweed

Orange hawkweed in bloom

Orange hawkweed (Hieracium aurantiacum) is a relatively new invasive weed in Clackamas County and we are working to keep it from becoming a common problem for landowners!

Orange hawkweed infests disturbed open areas

A member of the sunflower family, orange hawkweed is native to central and southern Europe and grows in open areas like roadsides, meadows, pastures, hayfields, and disturbed sites.  Orange hawkweed is a class A noxious weed here in Oregon, which means it is a “weed of known economic importance which occurs in small enough infestations to make eradication or containment possible”.  Class A noxious weeds are of such importance that you are required by law to report them to the Oregon Department of Agriculture, Noxious Weed Program within 48 hours of discovery.

The creeping stolons of orange hawkweed

Orange hawkweed was named by the Roman naturalist, Pliny the Elder, who thought that hawks consumed this plant to improve their eyesight.  While we are not sure if hawks eat this noxious weed, or if it improves eyesight, we do know that landowners should not count on livestock to graze it down.  Wildlife and livestock find it generally unpalatable and avoid it.

Also known as “devil’s paintbrush,” orange hawkweed produces orange flower heads that look similar to common dandelion.  Unlike dandelions, the flowering stems will have more than one flower, the stems are usually leafless, stiff, and covered with dense black hairs.  The above-ground runners known as stolons create a dense mat of plants that excludes other plants.  All parts of the plant exude a milky sap when cut.  Late spring through early summer is a great time to be on the lookout for this invasive weed.  Plants can reach heights between 10″ – 20″ inches. Orange hawkweed is the master of speedy reproduction and can propagate from both seeds and runners.

Why Should I Care About Orange Hawkweed?

Orange hawkweed infestation replaces lawns and landscape plants.

Orange hawkweed exhibits very aggressive growth.  In open areas where it invades, it can form a near-complete monoculture.  It readily displaces native plants through its dense growth and spreading roots.  Orange hawkweed also inhibits seed production in co-occurring plants by interfering with the pollination process of other plants. Its windblown dandelion-like seeds can spread great distances away from plants.  Each flower produces a generous amount of tufted seed which can lie dormant in the ground for years.

The WeedWise program has been busy working on orange hawkweed since 2011, and we have heard many accounts of property owners that were gifted several plants.  People are often surprised at the attractiveness of the plant and choose to cultivate the plant.  This decision is quickly regretted when the plants rapidly spread to kill other desired plants and quickly take over their yards and open spaces.

How Can I Control Orange Hawkweed?

Orange hawkweed seed heads

Prevention is the best method of controlling orange hawkweed!  This plant is still relatively rare in our state and we are working hard to stop this plant from spreading further.  To prevent the spread of existing populations of this invasive weed, carefully clean equipment, vehicles, boots, clothing, and pets after visiting an infested site.  Mowing can reduce seed production but may increase the vegetative spread.  Hand pulling can be effective for small infestations, but care must be taken to remove the deep, fibrous root and the creeping stolons.  Regular follow-up and persistence are required for any hand removal efforts.  Hand-pulled plants should be bagged up, disposed of as trash, or burned.  Do not dump pulled weeds, as this can often lead to new infestations.

For larger patches of orange hawkweed, we recommend using an herbicide application in spring, followed by hand pulling in early summer before seeds develop.  For more information on the chemical control of this invasive plant, please contact us.

Report Orange Hawkweed!

Have you noticed invasive orange hawkweed in your area? If so, please report your sightings to the Oregon Invasive Species hotline.  The WeedWise program has resources to help control this plant often at no cost to landowners.  So contact us today to help stop the spread of orange hawkweed.

For more information about orange hawkweed check on these resources:

Thank you for your help in identifying and reporting locations of orange hawkweed in our community!

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WeedWise Program