Boundary Invasive Species Society
Orange hawkweed (Hieracium aurantiacum) and Invasive yellow hawkweed (Hieracium and Pilosella spp.)
Identification:
Impacts:
Invasive hawkweeds spread rapidly and choke out grasses and native plants which reduces forage for both wildlife and other grazing animals. Biodiversity is very important to a healthy ecosystem and plants like invasive hawkweed, which produce dense mono-cultures, are bad news. If you have seen infestations of orange hawkweed in the Boundary, please report the location so it can be dealt with.
Management:
Hawkweed is being treated outside of the containment lines along some roads There is not enough funding to treat inside the containment lines. There is a bio-agent that is in primary release stage for orange hawkweed. We hope it will be effective. There are a number of very effective herbicides for hawkweed. Changing the nitrogen level in the soil can also help control hawkweed.
Orange hawkweed (Hieracium aurantiacum) has small infestations located across the district with the majority of sites in the Christian Valley, Carmi-Beaverdell area, Greenwood, and a few isolated patches up the Granby.
Invasive yellow hawkweed (Hieracium and Pilosella Spp.) has a large infestation in the Beaverdell–Carmi area. Isolated patches are present in the rest of the Boundary and the strategy is to treat all satellite infestations to keep this plant from spreading.​
Orange hawkweed has brilliant orange flowers, with a single stem with black hairs, and a rosette of leaves at the base of the plant, it is easy to identify. It is often introduced through “wild seed mixes” or by transplants from one garden to another. It spreads by seeds, stolons, and by under-surface lateral roots. A 1 m square patch of orange hawkweed can produce over 40,000 seeds per year!
Yellow invasive hawkweeds are a complex group of several introduced hawkweeds including yellow hawkweed (Hieracium pratense), meadow hawkweed (H. pilosella), yellow devil hawkweed (H. floribundum) and king devil hawkweed (H. piloselloides). They are a very difficult group to identify and a key has been developed to aid in identification for those familiar with botany. Invasive yellow hawkweeds spread mainly by windblown seed and once established will spread by stolons (above ground runners like strawberries) to form a dense monoculture.
