Weed of the Week: Hawkweeds
Attracting butterflies, birds, and bees with its dandelion-like features, invasive yellow and orange hawkweeds (Hieracium caespitosum
and H. aurantiacum)
began popping up around British Columbia as recently as fifty years ago, finding their way into backyard rock gardens and public landscapes as a gardener’s favourite perennial. Currently there are 14 invasive hawkweed species in BC, making them difficult to identify among the 8 native hawkweed varieties.
Hawkweeds are members of the sunflower family (Asteraceae) and are closely related to dandelions. Distinguishing characteristics of hawkweeds include bright orange, orange-red, or yellow ray flowers with several flower heads in clusters at the top of each plant. Leaves are long and oval-shaped, and cluster in a rosette formation at the base of fibrous, black-haired stems that contain a milky fluid. Hawkweeds can grow up to 30-60 centimetres in height.
Through intentional planting and accidental dispersal by human activities, wind, animals, and contaminated hay and soil, hawkweed blooms are now so visible throughout BC that many consider them a wild flower; however, this ‘wild flower’ is emerging as one of the most troublesome, aggressive invasive plants in the Pacific Northwest. The severity of its impact on the environment and the economy are only beginning to be realized.
It is no surprise that orange hawkweed is also termed “Devil’s Paintbrush,” and yellow hawkweed, the “King Devil,” as they are highly competitive and aggressively invasive, rapidly spreading through above- and below-ground runners, seeds, and root buds. Root buds sprout to produce new plants and are another form of vegetative reproduction used by hawkweeds. For instance, one plant can produce over 700 root buds in one growing season!
With several methods of reproduction, hawkweeds are high-speed invaders that can replace native vegetation in open, undisturbed natural areas, such as meadows and rangelands, reducing forage crops and threatening biodiversity. Hawkweeds are found at low to mid-elevations throughout most forest regions and regional districts in BC. Dense mats displace forage plants in hay fields and pastures, with infestations causing a reduction in crop yields and a rise in management costs. Hawkweeds further impact the forest industry, with a high risk of establishment and spread along forest service roads and harvested areas.
With no biocontrol agent available, the best way to control hawkweeds is with selective herbicides. In agricultural situations, hawkweed plants will not withstand regular tillage. Hand-pulling, even very small patches, is ineffective unless done with frequency and diligence to eliminate re-growth. Mowing down larger infestations will only serve to aggravate this invasive plant, potentially tripling its spread. Targeted grazing hawkweeds with sheep or goats may provide adequate control in some circumstances.
Once established, hawkweeds can be difficult to control or eradicate; thus, prevention is key!
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