Twin cress

Scientific name: Lepidium didymum

Twin cress flower

Twin cress

Twin cress flowers and twinned seed pods

Twin cress flowers and twinned seed pods

Twin cress flowers and twinned seed pods

Twin cress
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Young stems break easily but later become tougher and can sprawl for long distances
  • Flowers are small with tiny white petals and twinned fruits
  • Soft, finely divided leaves are hairless, 1-3 cm long and alternate on the stems. Cotyledons are long and club-shaped
  • Twin cress forms a disk-like mat of prostrate shoots radiating from the top of the tap root
  • Can be confused with wart cress and soldier’s button, both of which have similar leaves
  • Leaves have a strong smell when crushed.

Origin

  • Native to southern South America, twin cress is now found in most of the world’s dairying regions
  • First found outside South America in the UK near the end of the 18th century and first      recorded in New Zealand in 1846.

Life cycle

  • Twin cress can grow at any time of the year when temperatures are mild and moisture is adequate
  • An annual or biennial weed, new plants appear in early spring or autumn, especially in newly sown and overgrazed pasture or in winter or early spring sown crops
  • Self-pollinating (average seed production per plant is about 1600, and can be up to 18,000). Seeds are dispersed on muddy hooves, muddy footwear, and by ants and birds.

Benefits

  • Twin cress is used as a herb and added to salads in South America
  • Has a hot, strong flavour whether eaten raw or cooked
  • Plants have been used as a herbal remedy in some countries.

Occurrence

  • Twin cress grows throughout New Zealand, and is particularly plentiful in Southland and many districts of the North Island
  • Can grow densely in waste places, gardens and some crops, and is common in new lawns and young pastures.

Impacts on dairy products

  • Twincress can taint milk: a particularly bad season in 1987 meant that the Waitoa branch of the New Zealand Co-operative Dairy Company reduced the pay-rate of farmers supplying tainted milk ( – see references under ‘Further Information’)
  • This taint is often only detectable when the milk is heated during processing. It can cause the product to be down-graded at significant cost to the producer.

Impacts on pasture

  • Usually a slow growing, insignificant weed of crops which is outcompeted by other weeds. However, herbicides used to control other weeds may allow twin cress to become more dominant.

  • Twin cress seedlings in new pastures can be checked adequately with MCPB. Established plants become much more tolerant to MCPB, so spraying should be done while the seedlings are still small
  • In older pastures twin cress is less common and can be adequately controlled by MCPA or 2,4-D. The sprayed pasture should not be grazed for three weeks as plants are more palatable soon after spraying and can still taint milk
  • Although twin cress is reasonably tolerant to many herbicides, selective herbicides will provide good control of this weed in most crops.

  • Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.
  • Young S 2013. New Zealand Novachem agrichemical manual. Agrimedia Ltd., Christchurch, New Zealand. 767 p.