HPIPM:Orange hawkweed

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Asterales
Family	Asteraceae
Subfamily	Cichorioideae
Tribe	Cichorieae
Genus	Pilosella

Scientific Name

Pilosella aurantiaca

Scientific Name Synonyms

Hieracium aurantiacum

Common Name

orange hawkweed

Orange hawkweed (Hieracium aurantiacum)

Author: Jim Jacobs, Plant Materials/Invasive Species Specialist, USDA-Montana NRCS.

Adapted from the USDA NRCS Montana Invasive Species Technical Note “Ecology and Management of Invasive Hawkweeds (Hieracium Spp.)”

Identification and Life Cycle

Orange hawkweed (Hieracium aurantiacum) is a creeping perennial in the sunflower family (Asteraceae). Each hawkweed stem terminates in 1 to 50 bright orange dandelion-like flower heads. Each flower head ranges from 1/2 to 3/4 of an inch in diameter, and consists of 12 to 30 tiny orange florets, each capable of producing one seed. The seeds are black and have white hairs (pappus) attached to one end that facilitates wind dispersal. It produces basal rosettes with 5 to 8 narrow leaves 4 to 6 inches long. Up to 30 flowering stems with short stiff, black hairs can grow from each rosette. Stems produce a milky sap. Flowering stems can be leafless, or have 1 to 3 clasping leaves alternately arranged on the lower half of the flowering stems, the upper leaves smaller than the lower leaves. The dorsal leaf surface is dark green, the ventral leaf surface is light green, and the margins are entire or minutely toothed. Leaves are bristly with short hairs. Up to 12 leafy, creeping aboveground stems (stolons) can grow 4 to 12 inches from the flowering plants and can establish new rosettes. Orange hawkweed has a shallow, fibrous root system with a rooting depth from 1.5 to 4.5 inches and spread of about 4 inches.

Habitats

Sites most susceptible to invasion are roadsides, moist mountain meadows, forest meadows and clearings, permanent pastures, hayfields, cleared timber units, and abandoned farmland. Soils that are well-drained, coarse-textured, and moderately low in organic matter are most likely to support hawkweeds, but they can tolerate a full range of conditions from gravelly to acidic soils, full sun to partial shade, and frost and snow cover.

Impacts

Hawkweeds can form dense mats and choke out all other native vegetation in wildland settings. They cannot compete with crops due to herbicide use and many crops have a higher competitive ability. Hawkweeds are palatable species, fairly high in nutrients, so many grazing animals will eat them. However, they can form monocultures and choke out other desirable forage species. Infestations can spread to threaten lawns and gardens.

Biology and Ecology

Rosette leaves begin growth in April and usually grow upward at an angle to the ground except when growing under grazing pressure or harsh conditions. Rosettes can form from seed or from buds on stolons. Under ideal conditions, one orange hawkweed plant can spread by stolons and infest an area 2 to 3 feet in diameter in its first year of growth. Rosettes are intolerant of shading by competitor plants. The initiation of flowering begins in late May and peaks in mid-June. A second flowering period in September has been reported. Flowers open in bright sun and are pollinated by a number of insects including bees, flies, moths, butterflies, and beetles. Each flower head can produce between 12 and 30 seeds. Seed production can be as high as 13,000 achenes/square yard in ungrazed grasslands, but intensive grazing can prevent all seed production. Seeds remain viable in soil for up to seven years and can germinate as soon as they are released from the parent plant. Hawkweed populations are made up mostly of rosettes with densities of up to 3,200 plants per square yard. Population expansion within established patches is predominantly vegetatively from stolons that initiate from rosettes.

Management Approaches

Orange hawkweed is an excellent candidate for integrated weed management using combinations of fertilizer, herbicide, and seeding competitive plants.

Biological Control

No insects have been approved for release in the U.S. to control orange hawkweed.

Mechanical and Cultural Control

Fertilizers have been used to reduce hawkweed infestations on low productivity sites by increasing the competitiveness of desirable plants. Because hawkweeds have their perennial buds at the soil surface, hand pulling may be effective if rosettes and stolons are removed. Hand pulling may be practical where it can be repeated often on small patches, where there are competitive desirable plants in the community, and when combined with fertilization. Mowing hawkweed is ineffective for reducing populations because the low-lying rosettes, and stolons grow below most mower blade height settings. Grazing animals eat the flower heads of hawkweed, but the rosettes are not usually eaten. Therefore, grazing may have a similar effect on hawkweed populations as mowing.

Chemical Control

Herbicides can provide short-term control when applied in spring and early summer.

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.

References

For more information and images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=orange%20hawkweed