ENVS 605

What is it?

Orange hawkweed (Hieracium aurantiacum) is a perennial plant originating from Europe. It reproduces from runners, rhizomes, sporadic root buds, and seed. Leaves are basal with one or two small leaves occasionally occurring on the bristly stem. Rosette leaves are four to six inches in length spatula shaped and have finely toothed margins. The plant grows 10 to 20 inches in height. Flowers have 5 to 35 red-orange-yellow heads with petals that are trap-shaped with notched tips. The flowers generally grow in clusters, and look similar to dandelions. They range from 1/2 to 3/4 inches in size. The plant also contains a milky juice. Habitat for orange hawkweed includes disturbed areas, ski-fields, grasslands, pastures, rangelands, woodlands, alpine meadows and yards. It grows in temperate and mountain regions and can tolerate a variety of conditions (CSU, 08/08).

Taxonomists have been reclassifying more species -over 9000 species because the asexual seed reproduction have minor geographical versions. One distinct classification characteristic is where the hairness grows on what part of the plant and the hairs shape.

 

Why is it a problem?

Orange hawkweed displaces native vegetation and reduces livestock and wildlife forage. The plants quickly form dense infestations which dominate the site with a solid mat of rosettes or seedlings. Orange hawkweed readily escapes gardens and becomes a serious problem in natural areas. The seed viability of orange hawkweed is seven years. The site must be monitored for at least eight years after the last flowering adult plants have been eliminated and treatments repeated when necessary (CSU, 08/08). Hieracium species are now considered native to Africa, Asia, North America, Central America and South America

 

Management Techniques:

The key to effective control of orange hawkweed is preventing the establishment of plant communities through sound land management practices. Maintain healthy pastures and rangeland and continually monitor your property for new infestations. If plant populations of orange hawkweed exist, combining herbicides and cultural control methods can be effective (CSU, 08/08). 

 

Orange hawkweed is designated as a “List A” species in the Colorado Noxious Weed Act. It is required to be eradicated wherever found in the State. For more information visit www.colorado.gov/ag/weeds and click on the Noxious Weed Management Program. Or call the State Weed Coordinator at the Colorado Department of Agriculture, Conservation Services Division, 303-239-4100  

 

When native forbs and grasses are already present, assisting plant competitiveness by supplementing fertilizers can be an effective cultural control method. This proves to be most successful on pasture and rangelands where soil nitrogen levels may be depleted (CSU, 08/08).

 

Bio-control agents are not included in the prescribed management plans by the

State for List A Species. Eradication is the management objective of all List A’s.

No bio-control agent for Orange hawkweed is available. For more information on

Bio-control in Colorado, please contact the Palisade Insectary of the Colorado Department of Agriculture at 970-464-7916.

 

No mechanical controls recommended because of the weed’s ability to reproduce by stolons, rhizomes and root fragments. This often renders mechanical control obsolete.

 

Since orange hawkweed has been identified in small quantities around Colorado, preventing the populations from spreading is important in management of the weed. Using a combination of control methods proves to be the most effective way to control populations. Using cultural and herbicide control methods together proves to be key in eradicating established infestations (CSU, 08/08)

 

General Information on Orange Hawkweed:

Natural Resource Conservation Service

• Website that provides information, locations, classification, legal status, and related links

 

Colorado Department of Agriculture

• Website that provides identification, biology & control of Orange Hawkweed

 

Colorado Weed Management Association

• Website that provides information, habitat, identification, impacts, biology and control of Orange Hawkweed