Scientific name: Bellardia viscosa
- 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.
- 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.
- 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.
- Holden P 2021/2022. New Zealand Novachem agrichemical manual. Agrimedia Ltd, Christchurch, New Zealand. 864 p.
- Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Lincoln, New Zealand. 416 p.
- Breitwieser I, Brownsey PJ, Nelson WA, Smissen R, Wilton AD eds. (2010 -2021) Flora of New Zealand Online â€“ Weed Profile – Bellardia viscosa. (Accessed 4 October 2021)