Hieracium, subgenus  hieracium 
Hieracium, subgenus pilosella

Hawkweeds are hairy plants with stalked clusters of yellow flowers consisting of only ray flowers (dandelion-like).  Flower heads are joined to the hairy stems by leafy bracts. Wall hawkweeds have basal leaves and stem leaves. Meadow hawkweeds typically have basal leaves, but few to no stem leaves.  Basal leaves of most non-native hawkweed usually persist through flowering.

 Why are They Noxious Weeds?

Hawkweeds are invasive and spread readily. They are prolific seed producers and are weedy and capable of hybridizing with native and non-native species.  They are aggressive competitors for pasture, range and native plant species.

Hawkweeds prefer full sun, or partial shade. They infest meadows, roadsides and fields and are especially invasive on poorer acidic soils that are well drained and coarsely textured. They are aggressive competitors for pasture, range and native plant species.

Meadow hawkweeds spread by seeds and vegetatively by stolons, rhizomes, and auxiliary buds from root crowns. They also produce viable seed without pollination. The creeping growth of Meadow hawkweeds fills in the gaps between plants and forms mats of rosettes which prevent other plants from establishing seedlings. Non-native hawkweeds in the subgeus Pilosella include: whiplash (Hieracium flagellare), Yellowdevil (H. x floribundum), yellow or meadow (H. caepsitosum), queen-devil (H. glomeratum), pale (H. lactucella), mouseear (h. pilosella), and tall (H. piloselloides).

Wall hawkweeds  reproduce only by seed. Wall hawkweeds do not have stolons and grow from a single root base.  Non-native hawkweeds in the subgenus Hieracium include: European (Hieracium sabaudum), smooth (H. laevigatum), common (H. lachenalii), polar (H. atratum), spotted (H. maculatum), and wall (H. murorum). 

Yellow Devil and Yellow hawkweed are two of only six known pollen allelopathic plants. The pollen released from their flowers discharge toxins that inhibit the seed germination, seedling emergence, and saprophytic growth of surrounding plants.

• Early detection and eradication are important to prevent the spread of hawkweed. As usual with invasive species, the best control is prevention. Prevent plants from going to seed.   

• Hand pulling, or digging up isolated plants and small patches can help control hawkweed. Be aware that this noxious weed can reproduce from small root fragments, so it is important to get the whole root. Monitor the site where plants have been dug out for possible re-growth. Bag and dispose of all plants materials in the trash. Do not compost.

• Mowing is not effective as plants will send up shorter stems and quickly flower again. Plants will also put more energy into spreading by stolons and the infestation size and density will increase.

• Treatment with nitrogen will help other grasses to competitively suppress hawkweed growth.

• Triclopyr is very effective on most hawkweeds. Apply to actively growing plants, from spring to early summer before plants are fully in flower. Adding a surfactant is recommended.

• Spot spraying with an herbicide containing the active ingredient glyphosate may be used effectively in the spring while the plant is in the pre-bud to early bud growth stage. The goal is to insure all plants have emerged. Be aware, glyphosate is non-selective and will injure any plants that it comes in contact with, including grass.

• For selective control of hawkweed in agricultural settings (pastures, hayfields, etc.), an herbicide containing the active ingredient aminopyralid may be applied in the spring to plants in the pre-bud to early bud growth stage. It is also effective in the fall before a killing frost. Aminopyralid products will not harm grass and can be used around livestock provided all label precautions are followed.

• To minimize any harmful impact on bees and other pollinators, timing is important.  Ideally, treat plants before blooming.  If treatment after blooming is necessary, do control work early in the morning, or in the evening when bees are less active.

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels