tall hawkweed

Hieracium piloselloides

   

Family: Asteraceae

Weed Class:

Year Listed: 2013

Native to: Temperate Asia and Europe

Toxic: not known to be

Other Legal Listings:

additional photos

 

   

Why is it a noxious weed?

It appears to share the invasive characteristics of other hawkweed species already listed on the state noxious weed list as well as their negative impacts to rangeland and other habitats, especially in mid to upper elevations and in areas with low fertility soils.

How would I identify it?

General Description: This perennial, herbaceous plant does not have stolons, grows to 3 feet tall or taller and stem and leaves exude a milky sap when broken. Leaves are primarily basal, though sometimes with a few stem leaves near base of stem. Yellow flowerheads in loose clusters.

Flower Description: Flowerheads in open, round-topped clusters of typically 11-20, though can be more or less. Flowerheads composed of all yellow ray flowers with fused petals into a strap-like shape. Bracts at base of flowerheads have simple and gland-tipped hairs but do not have stellate (star-shaped) hairs.

Leaf Description: Leaves primarily basal, 3-8 (-20+), and there may be a few stem leaves at the base of the stem. Leaf blades are narrowly elliptic to narrowly egg-shaped and have smooth to toothed edges. Upper leaf surface hairless or with few hairs, lower surface has hairs along midvein.

Stem Description: Flower stems have hairs (1-2mm) that are simple, stellate (star-shaped) and/or gland-tipped.

Fruit/Seed Description: The seeds are 0.06 to 0.08 inches (1.5-2 mm) and have 20-40+ white bristles (pappus) in a single series on one end. Each seed is ribbed with minute barbs.

May be confused with: Many of the yellow flowering hawkweeds have a similar appearance. Linda Wilson’s “Key to the Identification of Invasive and Native Hawkweeds (Hieracium spp.) in the Pacific Northwest” Revised March 2007 is an excellent resource to identify hawkweed species.

How does it reproduce?

It can produce seeds and spread vegetatively by its rhizomes and root buds. Seed production is primarily through apomixis, the asexual formation of seeds, although occasionally sexual reproduction, outcrossing, and hybridization are believed to occur with some hawkweeds.
 

Where does it grow?

Tall hawkweed grows in shallow, coarse-textured soil, particularly along roadsides and in outwash areas. It has been documented in King, Snohomish and Grays Harbor counties.
 

How do I control it?

General Control Strategy

A long-term management strategy is needed to control invasive hawkweeds such as Hieracium piloselloides that promotes the establishment and growth of grasses and desirable plants. Make sure to monitor the area where the plants were removed for respouting roots and seedlings.

Mechanical Control

Mechanically controlling hawkweed species can be difficult to do in pastures and rangelands. Mowing plants to get rid of flowerheads only stimulates vegetative growth. If there are only a few plants, hand digging is a feasible option, but all of the roots must be removed. Once plants are dug up, put them into a city yard waste container or throw them in the trash. Do not put pulled plants in home compost piles as they might not get hot enough to kill them, and many species can vegetatively spread.

Cultural Control

Adding fertilizer and managing soil fertility has been used to effectively control hawkweed species in some areas, especially where populations are small or new.

Herbicide Control

Control of non-native hawkweeds infestations have relied extensively on selective herbicides, which can be effective, but reinvasion can occur unless other plants can fill the gaps left by the hawkweed removal. Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.


 

For more information

 
See Linda Wilson's key on PNW hawkweeds for more information about keying hawkweeds in the Pacific Northwest.
See our Written Findings for more information about tall hawkweed (Hieracium piloselloides).

Additional Photos


 
 

 


Roadside infestation

 


Blooming flowerheads

 


Blooming flowerheads on long flower stems

 


Plants with developing flower stems and flower buds

 


Infestation

 


leaf underside

 


infestation

 


inflorescence

 


blooming flowerheads

    

back to page top