Orange Hawkweed

Description

Orange hawkweed was introduced to North America as an ornamental species towards the end of the 19th century in the eastern United States. Within 25 years it had spread from New England to Michigan and is currently one of the most widespread invasive plants in North America (Wilson and Callihan 1999). Orange hawkweed is a creeping perennial with milky sap and shallow fibrous root system (Wilson and Callihan 1999). The basal rosette of hairy leaves and cluster of dark orange compound flowers at top of a 0.3 to 1.2 m tall leafless flower stalk serve to distinguish this species from other hawkweeds in British Columbia.

Type

Perennial

Habitat & Impacts

Orange hawkweed occupies a wide range of well-drained habitats but prefers coarse soils and unshaded sites.

Method of Spread

It reproduces by seed, stolon, or rhizome and can form large continuous mats with up to 3500 plants per square metre (Wilson and Callihan 1999). Seed production is generally low, but seeds can be produced sexually or asexually without pollination. Seeds are mostly dispersed by animals, people, or vehicles. Although seeds are plumed, they are not spread widely by wind. Seeds can remain viable in the soil for more than 7 years although most germinate within one year of production.

Location

Orange hawkweed is currently concentrated in the eastern part of the Cariboo Chilcotin Coast from east of 100 Mile House to the northern boundary but there are sites along the length of Highway 97. Scattered sites are recorded in the Chilcotin, and it is not recorded in the coastal areas of the region.

Mechanical

Hand pulling of young plants can be effective but small root fragments can sprout and allow the infestation to persist. Mowing can control seed production but encourages vegetative growth and spread. Digging plants or otherwise disturbing roots can help spread since new plants can become established from root, stolon, or rhizome fragments (Wilson and Callihan 1999). Orange hawkweed should not be tilled unless this treatment is done in combination with a chemical treatment and followed by reseeding.

Chemical

Dicamba, Picloram, Aminopyralid, Clopyralid, or Picloram and 2,4-D are effective active ingredients that control orange hawkweed during the spring growing season.

Biological

Biological control agents are currently being developed, and once available may change the management approach to this species.

Cultural

Ammonium Sulphate (Nitrogen fertilizer) can be applied to fields to suppress the competitive edge of orange Hawkweed. 

CCCIPC Priority & Treatment Strategy

Priority 1 (new invader) in the Chilcotin and Central Coast, Priority 2 (containment) in the Central and South Cariboo, and Priority 3 (established) in the North Cariboo and Nazko. Preventing additional sites from establishing in western parts of the region is a priority. A containment area is established east of Highway 97 along the Interior Douglas Fir/Sub-Boreal Pine Spruce Biogeoclimatic zone boundary to Williams Lake, then along the West Fraser Road to Narcosli/Deep Creek then west to the Itcha Mountains (see maps in Appendix 6). All sites outside the containment line will be aggressively controlled.

Local Level

Hand pulling new and small infestations, chemical, and fertilization for large sites.

Landscape Level

Chemical treatments.