Hieracium floribundum • Class A

The plant has a basal rosette of narrow, pointed leaves, which are covered with a whitish or bluish waxy coating. The top of the leaf is smooth while the underside has scattered, bristly hairs, particularly along the mid-rib. The single flowering stem grows up to 32 inches tall, and is sparsely covered with bristly blackish hairs. In mid to late spring the stems are topped with 3 to 50 bright yellow flower heads in a flat-topped cluster, closely resembling a dandelion. 

Its creeping growth fills in the gaps between other plants forming mats of rosettes and prevents other plants from establishing seedlings. 

It infests meadows, roadsides and fields and is especially invasive on poorer acidic soils. It prefers full to partial sunlight. 

Yellow Devil hawkweed is one of only 6 known Pollen Allelopathic plants. The pollen released from its flowers discharges 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 measure for Yellow Devil Hawkweed is prevention. Above all, prevent plants from going to seed. 

• Hand pulling or digging up isolated plants and small patches can help control Yellow Devil Hawkweed. Be aware that this species of hawkweed 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 the plants in the garbage. Do not compost. 

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

• Early season treatment with 2, 4 D plus dicamba (as in Weedmaster, etc.) can be an effective chemical control for Yellow Devil hawkweed. 

• Spot spraying with an herbicide containing the active ingredient glyphosate (Roundup Pro, Glyfos, etc.) 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. Spray each plant thoroughly on the stems and leaves, enough to be wet but not dripping. 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 (example: Milestone, Milestone VM, etc.) 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). 

• When using herbicides, always read and follow all label instructions and obey all label precautions. (Note: pesticide product registration is renewed annually and product names and formulations may vary from year to year.) 

There are no known biological control agents for use on hawkweeds in the United States. 

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