Montana Field Guide

PLANTS: Perennial forbs with erect stems from 10-35 (70) cm tall that are rhizomatous and stoloniferous. Rhizomes have fibrous-roots. Stems are single (simple). Stems have stiff hairs (hirsute) of 2-4+ mm that may become shorter and stipitate-glandular upwards. Sources: FNA 2006; Lesica et al. 2012.

LEAVES: 3-8 basal leaves and 0-1 stem leaf. Basal leaves 3-15 cm long, petiolate, blades spatulate to oblanceolate, margins entire, and tips acute. Leaf surfaces with stiff hairs (hirsute) of 1-2+ mm long and stellate-pubescent.

INFLORESCENCE: More-or-less umbelliform. Burnt orange flower heads of 3 to 12, clustered, and pedunculate with stellate pubescence and stipitate-glandular hairs. The involucres are campanulate, 5–9 mm high. The involucral bracts (phyllaries) are linear-lanceolate with acuminate tips, and are stellate-hairy, stipitate-glandular, and sparsely setose-hirsute. Flower heads composed of 25 to 100 florets with petals red to orange, 6–8 mm long. The pappus are white bristles of 3.5-4 mm long. Fruits (cypselae) are columnar, about 2 mm long, and retain the tuft of bristles (pappus).

Flowering May – September (FNA 2006).

Montana has about 4 native and 3 exotic species of hawkweeds.

Orange Hawkweed is the only hawkweed in Montana with red-orange flower heads. Flower heads are composed of only ray florets.

Orange Agoseris Agoseris aurantiaca also has orange to pink, ligulate flower heads, but the plants are not hirsute hairy and the basil leaves are larger and oblanceolate. It grows in meadows and rocky slopes.

Disturbed soil of forest openings, rock slides, roadsides, lawns; valleys to lower subalpine (Lesica et al. 2012).

The loss of biodiversity is the most prevalent threat posed by Orange Hawkweed.

HABITAT VULNERABILITY
In their native habitats of northern and central Europe, Meadow and Orange Hawkweeds are species of pastures, roadsides, abandoned fields, and meadows that form small populations (Skalinksa 1967). In the northern U.S. these plants appear to pose the greatest threat to cooler, sub-humid to humid habitats.They have invaded moist pastures, forest meadows, abandoned fields, clearcuts, and roadsides from valleys to montane (Skalinksa 1967; Lesica et al. 2012). These habitats that also have well-drained, coarse-textured soils low in organic matter appear the most vulnerable to invasion by Orange Hawkweed (Wilson and Callihan in Sheley and Petroff 1999). Once established plants quickly grow into a matt of dense rosettes (Wilson and Callihan in Sheley and Petroff 1999). Consequently, elk habitat, recreational areas, and pristine mountain meadows are especially susceptible to invasion (Wilson and Callihan in Sheley and Petroff 1999). Drier rangeland habitats are not suspected of being vulnerable (Wilson and Callihan in Sheley and Petroff 1999). Meadow and Orange Hawkweeds apparently do not survive in annually-tilled cropland (Wilson and Callihan in Sheley and Petroff 1999).

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus ternarius, Bombus terricola, Bombus bohemicus, and Bombus flavidus (Heinrich 1976, Colla and Dumesh 2010).

Orange Hawkweed plants reproduce by seed, rhizomes, and stolons.

From the rosette, plants produce one flowering stem. Plants are often apomictic, that is reproducing from asexually produced seeds (FNA 2006). Apomictic reproduction creates morphological variants that perpetuate at population and regional levels (FNA 2006). This can make identifying hybrids difficult. Very few seeds are produced sexually through pollination and out-crossing (Wilson and Callihan in Sheley and Petroff 1999). Flowering in a related species, Hieracium floribundum, was found to occur upon exposure to a specific amount and quality of light (Wilson and Callihan in Sheley and Petroff 1999).

Mature seeds can germinate immediately after dispersal and be viable for up to seven years (Wilson and Callihan in Sheley and Petroff 1999). In a study of Hieracium floribundum only 1% of new plants were born from seeds (Thomas and Dale 1974). The study also found that 80% of the seeds dispersed within the colony with only 1% of the seeds travelling greater than 30 feet (10 meters) from the patch. Another study found seedlings that germinated in spring had better survival rates than those germinating in summer or winter (Johnson and Thomas 1978).

PREVENTION [Adapted from Sheley and Petroff 1999]
Successful management seeks to prevent infestations and detect them before the patch spreads vegetatively. Large infestations are difficult to control. Using multispectral, digital images may identify infestations in remote areas better than visual surveys over large areas (refer to Carson et al. 1995).

CHEMICAL CONTROL
The Phenoxy-type herbicides (2,4-D, clopyralid, and picloram) are effective in controlling orange and meadow hawkweeds when applied to the rosette stage and used with a surfactant (Wilson and Callihan in Sheley and Petroff 1999). The herbicide type and concentration, timing of chemical control, soil properties, and other factors will determine its effectiveness and impact to non-target species. Strict adherence to application requirements defined on the herbicide label will reduce risks to human and environmental health. Many herbicides must be applied by applicators with an Aquatic Pest Control license. Consult your County Extension Agent and/or Weed District for more information on herbicidal control.

Greenhouse and field studies conducted in southern Alaska by the Agricultural Research Service examined the effectiveness of aminopyralid, clopyralid, picloram, picloram+chlorsulfuron, picloram+metsulfuron, and triclopyr herbicides in controlling orange hawkweed (Seefeldt and Conn 2011). Only aminopyralid at 105 g ai/ha and clopyralid at 420 g ai/ha controlled orange hawkweed consistently, with peak injury observed one year after treatment. Clopyralid had less impact on non-target species with most recovering the year after treatment. In a pasture system, where grasses are preferred to forbs and shrubs, aminopyralid is preferred because it controls a broader array of forbs compared to clopyralid. In natural areas, where the desire is to retain biodiversity and the aesthetics of multiple forb, grass, and willow species, clopyralid is preferred because it will leave a greater species diversity than aminopyralid.

Researchers at the University of Idaho found more than a 50% control of hawkweed using clopyralid at the rate of 0.5 lb ai/ac (Wilson and Callihan in Sheley and Petroff 1999). A similar control was found using picloram at the rate of 0.2-0.5 lb ai/ac.

A combination of fertilizers and herbicides applied to areas where hawkweed is mixed with perennial grasses, legumes, and other forbs can reduce spreading (Wilson and Callihan in Sheley and Petroff 1999). Fertilizer treatments reduced hawkweed density and vigor in the U.S., Canada, and New Zealand. Depending upon soil productivity and grass condition, fertilizers can promote the growth of desirable plants which may become competitive enough to suppress hawkweed growth.

CULTURAL & GRAZING CONTROLS [Adapted from Wilson and Callihan in Sheley and Petroff 1999]
Hand-pulling and mowing are not effective control measures. Physical disturbance to orange hawkweed severs roots, stolons, and/or rhizomes causing the plant to further spread. Mowing may remove flowering stems and reduce seed production but will not hinder growth by the stolons or rhizomes. Soils disturbed by livestock, rodents, or people can also enhance the plant to spread.

BIOCONTROL [Adapted from Wilson and Callihan in Sheley and Petroff 1999]
In 1995 the USDA Agricultural Research Service in Bozeman, Montana began to develop the feasibility of a biological control program for orange and meadow hawkweeds. However, biological control for these plants has not yet successfully been developed in the U.S.

Useful Links:
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage.
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides

The loss of biodiversity is the most prevalent threat posed by Orange Hawkweed.