Weed of the Week - Yellowdevil Hawkweed
Weed(s) Of The Week #8
Yellowdevil Hawkweed (Pilosella glomerata AKA Hieracium glomeratum)
Tall Hawkweed (Hieracium piloselloides)
Currently Unregulated But Being Considered For Listing Under Alberta's Weed Control Act
Submitted By Kelly Cooley, CoolPro Solutions
Both of these yellow flowered close cousins to our previous Weed Of The Week, Orange Hawkweed, grow a bit taller than their orange-petaled relative.
Both Yellowdevil and Tall Hawkweed seeds germinate in the spring and form lance-shaped leaves in ‘rosettes’ close to the ground, though Yellowdevil Hawkweed’s leaves are much more hairy than Tall Hawkweed. Both species eventually generate solitary and leafless though hairy stems – Tall Hawkweed grows slightly higher than Yellowdevil Hawkweed. All leaves and stems on both species yield a milky white sap if broken open. Both species’ stems eventually yield a cluster of buds that open in late June to early July to reveal yellow flowers (see photos), with Tall Hawkweed flowers being larger and less numerous than those of Yellowdevil Hawkweed. Both species are highly invasive creeping perennials that spread via rooted clumps tied together by shallow lateral roots. Unlike Orange Hawkweed, these two yellow-flowered hawkweeds do not use ‘runners’ (stolons) to reproduce. There is some evidence that several yellow flowered invasive hawkweed species in our region can hybridize, making positive identification difficult.
Both Yellowdevil and Tall Hawkweed have spread widely in the Castle Wildland Park and Livingstone Public Land Use Zone in the wake of the 2003 Lost Creek Fire. Both species are aggressively moving east of provincial public land areas downstream and down-road into agricultural pastures. While many herbicides are capable of controlling both species, once they have flowered, viable seeds still can form after spraying.
Landowners who spot these two yellow hawkweed species on or near their land should immediately take measures to bring infestations under control before they spread. Learning to spot these hawkweeds pre-flowering will aid in control. More information on these and other yellow flowered invasive hawkweed species can be found in the fact sheets found on the Alberta Invasive Species Council website (scroll down until you find the various Hawkweeds). You can report invasive hawkweeds yourself using their free EDDMapS application on your mobile device. For local Hawkweed control options, please contact our Agricultural Fieldman at 403-339-8741.
Photo Credits: Kelly Cooley, CoolPro Solutions
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