Common Hawkweed
Hieracium lachenalii

Common hawkweed is a fibrous-rooted perennial with upright stems and small, dandelion-like flower heads in loose clusters. A European species, common hawkweed is invasive in northwestern and northeastern North America, especially in woodlands, fields and roadsides. Like other hawkweed species, this plant is highly invasive and will spread over large areas if not controlled.

Common hawkweed is a Class C Noxious Weed in Washington State, selected by the King County Noxious Weed Control Board for county-wide control. Public and private landowners are required to control this plant when it occurs on their land.

Identification

• Stems upright, up to 2 1/2 feet tall, hairy, leafy, and topped by 4-12 small yellow flowers heads in an open, round-topped cluster
• Stems have a milky juice
• Leaf edges strongly toothed, leaf bases tapered and narrowing
• Leaves at base of stems are grey-green in color, broadly elliptical or lance-shaped, and still present when plants are flowering
• Stems have 4-7 leaves, smaller and lacking a stalk (petiole)
• Flower heads have white hairs around the base

Habitat and Impact

Common hawkweed is found mostly in open fields, mountain meadows, forest clearings, permanent pastures, cleared timber units, abandoned farmland, roadsides and other disturbed areas. Typically found where soil is well-drained, coarse-textured, and low-nutrient.

In the Pacific Northwest, hawkweeds are most abundant in middle elevations from 2000 to 5000 feet, but they are also found in lowland areas, especially along highways and roadsides.

Growth and Reproduction

Common hawkweed reproduces by seed. Because seed production is mostly asexual, hawkweeds do not depend on pollination and can rapidly dominate an area due to its high seed production. Hawkweeds are perennials and can thrive in a wide range of conditions. Seeds can disperse long distances.

Control

Small populations can be removed by digging. Make sure to remove the entire root since plants can resprout from root crowns. If plants are in flower, bag and discard flowering stems to avoid spreading seeds.

Do not control by mowing unless mowers can be cleaned before moving to new areas and all the flowering stems can be collected and discarded. Plants will re-grow after being mowed and flower again in the same season.

Large areas infested with hawkweed are highly difficult to manage. In areas where hawkweed is still limited in distribution, every effort should be made to contain and reduce the hawkweed before it is too established to control.

Selective herbicides have been most successful in managing hawkweed because they allow the grass to remain in place, greatly reducing the germination of hawkweed seeds in the soil and slowing down re-invasion by the hawkweed.

Hawkweed management needs to be combined with altering the conditions in the plant community to favor grasses and native plants. If holes left after controlling hawkweed are not filled quickly with desirable species, hawkweed is likely to re-infest the area. Since hawkweed often grows in low-nutrient, low-organic soils, amending the area with fertilizer and organic matter can help reduce re-infestation by hawkweed when combined with active management of the hawkweed.

Make sure to have a long-term plan to ensure success, protect native and beneficial species while doing the control, and start in the least infested areas first and then move into the more heavily infested areas.

For Photos and More Information on Common Hawkweed (Hieracium lachenalii)

Written Findings of the Washington State Noxious Weed Control Board (pdf file, requires Acrobat Viewer)

USDA-NRCS Plants Database Profile for Common Hawkweed (external link)

Photos and Distribution from the University of Washington Burke Museum (external link)

University of Idaho Hawkweeds Website (external link)