Scientific name: Bellardia viscosa
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Upright, single-stemmed herb, to 60 cm high
  • Sticky, hairy leaves and stems
  • Rough, toothed, lance-shaped leaves 45 by 15 mm
  • Yellow, snapdragon-like flowers emerge from leaf axils progressively up the stem.


  • Native to western Europe and the Mediterranean, introduced to New Zealand around 1875.


  • Tarweed is found throughout New Zealand, growing in damp pastures, roadsides, waste places, lake margins and stream sides.

Life cycle

  • Tarweed is an annual, semi-parasitic herb which attaches to a wide range of host plants soon after germination. It is a prolific seeder, releasing thousands of very small, 0.5 mm long seed each year. Tarweed gains a competitive advantage by robbing nutrients from the host plant in addition to producing nutrients (sugars) through its own photosynthesis.


  • There are no known uses for tarweed.

Impacts on pasture

  • Tarweed robs nutrients from host plants, reducing their growth and production.

Impacts on forage crops

  • Tarweed is rarely found in fodder crops, possibly due to insufficient soil moisture.

Impacts on stock

  • Mature tarweed plants tend to be avoided by grazing animals due to their sticky, hairy nature.
  • Tarweed is not known to be poisonous.

Grazing and cultural management

  • Young tarweed plants may not survive intensive mob stocking, but once established they will not be grazed
  • Tarweed may be controlled by mowing
  • Improving pasture competition is recognised as the best cultural method for control.

Chemical control

  • Tarweed is readily controlled by the phenoxy herbicides MCPA and 2,4-D up to flowering
  • It is not susceptible to 2,4-DB or MCPB.


  • There are no legal biosecurity issues with tarweed, however, it should be considered best practice to not make hay from infested pastures and certainly not to accept contaminated hay onto a different property.