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Orange Hawkweed

Posted by cahnrs.webteam | November 13, 2013

Also Known As: devil’s paintbrush, fox and cubs, king devil

Orange Hawkweed is a Class B Noxious Weed. Class B noxious weeds are nonnative species whose distribution is limited to portions of Washington State. In some regions where a class B species is already abundant, control is decided at the local level.

Orange Hawkweed (Hieracium aurantiacum L.) Orange hawkweed, a perennial plant of the sunflower family, originated from Europe. The hawkweed plant spreads by seed, stolons, rhizomes and root buds, and has a shallow, fibrous root system. The plant stem extends from a basal rosette of hairy, lance-shaped leaves that are 4 to 6 inches long. The stem reaches a height of 10 to 20 inches, and is usually leafless, although occasionally a leaf will appear mid-stem. Stiff, glandular hairs cover each erect, slender stem. The plant leaves and stem exude a milky latex when broken. Atop the stem is a cluster of bright orange-red, dandelion-like flowers that typically appear in late May or June and flower into early fall. Each flower measures about ½ to ¾ inch in diameter and has notch- tipped, square-edged petals. The flowers tend to close up when the plant is shaded. Each flower bears 12-30 tiny, plumed seeds that are generally dispersed by wind and water. Hawkweed seeds can also be transported in contaminated soil and are sometimes found in wildflower seed mixes. The seedsImage_006 remain viable in the soil for up to 7 years.

An orange hawkweed plant sends out 4–8 stolons each season. The extensive stolons can create dense mats, which displace desirable vegetation and reduce forage for livestock and wildlife. Not only is orange hawkweed an aggressive competitor of pasture and range plant species, but it is unpalatable to animals and is also reportedly allelopathic, producing phytotoxic chemicals in its pollen grains that inhibit other plants from regenerating. Orange hawkweed generally inhabits moist grasslands, shady area sand disturbed soils. Hawkweeds do not persist in cultivation.

 

 

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 Control Methods

Prevention of orange hawkweed is the preferred method of control. This involves monitoring property to allow early detection of weed infestations and managing desirable vegetative species to give them competitive strength against weedy invaders such as hawkweed. Orange hawkweed should never be used as a garden ornamental, and wildflower mixes should be avoided to prevent accidental introduction of invasive species.

Mechanical: Because orange hawkweed can resprout from any fragments left in the soil, mechanical control is limited. Small infestations of hawkweed can be hand dug, although all vegetative parts of the plant must be removed to prevent plant regrowth. Although mowing may prevent seed set, mowing actually promotes flowering and the spread of stolons. After control measures are taken, the site should be monitored over the long term for plants growing from root fragments or from seed.

Chemical: Several herbicides offer effective control of orange hawkweed. Growing plants can be controlled with clopyralid, picloram, or combinations of these herbicides with 2,4-D. A surfactant should be added to the mix to ensure adherence of the herbicide to the plant’s hairy leaves. Early season treatment applied at the rosette stage provides optimal control. Retreatment may be necessary.

More information can be found in the PNW Weed Management Handbook

Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Biological: No biological control agents are currently available for orange hawkweed.

Questions: contact Steve Van Vleet or phone (509) 397 – 6290

Photo credits included in PDF

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