Hieracium, hawkweed

Scientific name: Hieracium and Pilosella spp.

King-devil hawkweed flowers

Mouse eared hawkweed

Mouse eared hawkweed flowerhead

King-devil hawkweed

King-devil hawkweed flowerhead

Orange hawkweed flower

Orange hawkweed plant in pasture
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • All the plants listed here are included on the National Pest Plant Accord, which means they cannot be grown, distributed or sold in New Zealand.

Distinguishing between species

Mouse-eared hawkweed (Pilosella officinarum)
  • Rosette-based perennial plant producing creeping grey-white stolons which spread outwards and form large, dense mats that exclude other vegetation
  • Pale lemon-yellow flower heads (often with a red stripe on the outer face of the petals) that occur singly on a leafless flower stalk
  • Leaves lie flat on the ground and have white edges that are often upturned
  • Long hairs are scattered on the upper surface of the leaves. The undersides are felt-like and covered in dense, star-shaped hairs
  • Sap is milky-white
  • Common in high-country and dry pasture land, river flats, forest margins and roadsides.
King-devil hawkweed (Pilosella piloselloides subspecies praealta)
  • Multiple clusters of bright yellow flowers on tall red stems
  • Small leaves at the base of the flower stalk are green to red in colour
  • Leaves are erect with their edges folded in
  • 2 – 5 mm long hairs on the mid-rib and edges of leaves
  • Milky-white sap
  • Common in modified tussock grassland, roadsides, river terraces scrub and pasture.
Orange hawkweed (Pilosella aurantiaca)
  • Multiple clusters of attractive orange flowers, with each ‘flower’ about 2 cm across
  • Rosette  leaves are lance-shaped, with upturned edges and long simple hairs scattered on both upper and lower surfaces
  • Sap is dirty white
  • Mostly found in the North Island. Common in waste areas, modified tussock grassland, river terraces, lawns and pasture.
Less common species present in New Zealand:
  • Tussock hawkweed (Hieracium lepidulum) has few bright yellow flowers at the top of the stalk. In the North Island it is only found on Mt. Taranaki, but in the South Island it occurs in Nelson, Marlborough, Canterbury and Otago
  • Field hawkweed (Pilosella caespitosa) is only found in the South Island (Marlborough, Canterbury, Otago), and has green leaves that are softly hairy on both surfaces.

Origin

  • Native to Europe and deliberately introduced, hawkweed persists as an invasive weed in many parts of the North and South Islands.

Life cycle

  • Initially plants establish from seed and then spread by daughter plants produced by creeping stolons
  • These weeds are invasive and can be very hard to control
  • Plants form a solid mat which excludes other pasture species
  • Plants flower in spring and later produce seed heads
  • Seeds are black, with a long hairy pappus attached which protects the seed and aids to some extent in wind dispersal
  • Seeds are ribbed with small hairs that allow them to stick to fur, clothing and vehicles.

Benefits

  • Provides nectar for bees and other insects.

  • While hawkweed is readily grazed by stock it is very low growing and hard for livestock to reach
  • The quality of pasture is reduced – especially in areas heavily infested with hawkweed
  • Stocking rates are reduced and gross annual revenue losses result. In 1993 this loss was estimated to be $45 million per annum for New Zealand.

Grazing management

  • Appropriate grazing management is one of the best methods for controlling hawkweed invasion and spread on unfertilized or low-input land
  • Hawkweed species are restricted by grazing but rapidly increase in ungrazed pastures. Therefore, frequent grazing is the easiest method of hawkweed control
  • Spring grazing greatly reduces hawkweed flowering, as flowerheads are palatable to stock. This leads to a lower reproduction rate of the weed.

Fertiliser

  • Hawkweed populations decrease under fertiliser application. Sowing new pastures helps to provide competition and suppresses hawkweed
  • The weed is highly invasive under low fertility; maintaining soil fertility is important for the control of hawkweed.

Grubbing

  • Grubbing can be an effective method of control for small infestations. However, it is important to remove all stolons or the plant may re-grow.

Chemical control

  • Chemical control of hawkweed is difficult because most herbicides do more damage to the surrounding pastures than to the weed
  • In trials 2,4-D has shown promise in controlling hawkweed.

ALWAYS READ PRODUCT LABELS BEFORE APPLYING

Active ingredient When to apply Residual effect Grass damage Clover damage
2,4-D Spring Slight No Slight

Consult your farm consultant, industry rep or New Zealand Agrichemical Manual for more information about chemical control.

Forestry

In areas of steep hill country where infestations are large and management options are limited consider forestry plantations. Not only will this wipe out the hawkweed infestation but may increase farming profits once trees have established.