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Hieracium aurantiacum

Hawkweed Nomenclature & Identification – February 2013 MSU Weed Post

Friday, February 1st, 2013

 

The hawkweeds are difficult taxonomically and morphologically due to hybridization and agamospermy (the production of seeds without fertilization) .  So we hope this Weed Post  will provide you with a variety of resources to approach the hawkweeds with more confidence.  Download February 2013 MSU Weed Post

Visit the MWCA Weed ID page for details about orange hawkweed or meadow hawkweed complex. Contact your local weed coordinator if you think you find it in your area.


Hawkweeds – January 2013 MSU Weed Post

Tuesday, January 1st, 2013

 

MSU is starting the third year of the Weed Post with information on hawkweeds. Download the January 2013 MSU Weed Post

Visit the MWCA Weed ID page for details about orange hawkweed or meadow hawkweed complex. Contact your local weed coordinator if you think you find it in your area.


Weed of the Week – Orange Hawkweed

Thursday, October 28th, 2010

 

Orange hawkweed is native to Europe and likely came to the U.S. as an ornamental.  It has since escaped cultivation and was first found to be a problem in Spokane, WA in 1945.  There are serious infestations in northwestern Montana, northern Idaho, and northwestern Washington.

Orange hawkweed’s clusters of bright orange to orange-red dandelion-like flowers make it unmistakable.  The orange flowers follow the path of the sun throughout the day and if the plant is broken off it exudes a milky latex substance.  There are several native species of hawkweeds in Montana but orange hawkweed can be distinguished by its orange flowers (it is the only species with orange flowers), bristly hairy leaves (most other species have smooth leaves), and stiff black hairs up the stem.

Concerns Orange hawkweed is a great concern because of it ability to reproduce several ways.  The clusters of 5-30 flowers produce between 12 and 50 seeds per flower and these seeds remain viable in the soil for up to 7 years.  This plant can also spread or reproduce from stolons (above ground runners), of which it produces an average of 6 per year, rhizomes (underground horizontal roots), or adventitious root buds (buds on the roots that can develop into a new plant at any point).  Not only does it have the ability to spread in a variety of ways but it is also believed to be allelopathic (exudes toxic chemicals into the soil that suppress surrounding vegetation).  The combination of these abilities makes it a very aggressive species that can rapidly create large, dense monocultures pushing out not only native, beneficial vegetation but also established lawns.

Identification This perennial has a basal rosette with many hairy leaves and a leafless, hairy stem that can be up to 30 inches tall.  Each rosette is capable of producing 10-30 flower stems, each of which have 5-30 orange flowers that are arranged in a flat-topped cluster.  The flowers are bright orange to orange-red and dandelion-like in appearance, with square ended petals.

What can you do? Due to the extensive root system of orange hawkweed hand-pulling and digging-up large infestations is not an effective means of control.  Very small infestations may be controlled by these methods but care must be taken to remove all of the root system because even the smallest fragment can produce a new plant.  Mowing is not recommended because it actually encourages the growth of this plant.  There are several herbicides that are effective in controlling orange hawkweed and re-seeding is always recommended to fill in the areas where this plant was removed.  If you have any questions regarding orange hawkweed or any other weed call your local weed district.

Visit the MWCA Weed ID pages for additional information and pictures of orange hawkweed.

This series of articles was developed by Ravalli County.  If you would like to use these articles please contact Ravalli County Weed District Weed Coordinator at (406) 777-5842.