Environment

Nodding thistle

Nodding thistle.Nodding thistle.

Common name:
Nodding thistle, musk thistle, nodding plumless thistle

 

Scientific name:
Carduus nutan

 

Regional classification:
Total control - you are required to control

 

National classification:
National Pest Plant Accord – banned from being sold, propagated or distributed

Description

Nodding thistle is an erect biennial (sometimes annual) thistle, growing to about 1.6 metres high, reproducing by seed only. It has a stout, branched, fleshy taproot up to 40cm deep.

 

Stems:

  • flowering stems are often branched in their upper half
  • bear spiny “wings” to just below the flower head

Leaves:

  • rosette (basal) leaves are usually long and narrow
  • deeply cut into narrow lobes with spiny edges
  • upper leaf surface has metallic sheen and a whitish edge, especially around the base of the spines.

Flowers:

  • thistle rosettes can be up to 60cm across
  • easily recognised by its large flower heads which droop or nod when mature

Nodding thistle can be confused with the more common Scotch and winged thistles.  Scotch thistle leaves have small prickles on their upper surface as well as the edges.   Its heads are purple and winged thistle heads are small and pinkish-white.  Winged thistles are usually whitish on the underside of the leaves with the upper surface being paler green with clearly defined whitish veins.

Why is it a problem?

Nodding thistle is a major agricultural pest, smothering grass and forming a total groundcover that prevents stock movement.

 

Nodding thistle seeds are spread between properties mainly by contaminated hay and machinery, uncertified seed and stock feed.  Seeds remain viable in the soil for several years.

 

Nodding thistle prefers light soils and low-medium rainfall but will grow in most sunny, free draining sites with little ground cover.  Therefore all cropland and pasture subject to drought or insect attack is at risk.

 

The plant cannot compete with long pasture.

 

Plants which are mowed may persist as perennials until they are able to flower, thereby becoming harder to kill.

What can I do?

Isolated plants:

  • Grub out removing at least 5cm of taproot, or spot herbicide treatment.

Larger infestations:

  • Spot spray or grub mature plants not susceptible to the broadcast spray chemical.
  • Graze area prior to broadcast spraying to reduce clover leaf and to expose seedlings.
  • Broadcast spray during the late autumn or early spring period to remove seedlings and small plants.
  • Follow up with spot spraying or grubbing to catch late germinating or missed plants.
  • Infested areas must be checked at least twice yearly to ensure that plants do not seed.
  • If left to establish, nodding thistle can be very difficult to eradicate.
  • Grub or spray plants before they flower.
  • Keep a tight sward of grass and do not overgraze. This prevents germination or suppresses the majority of seedlings before they develop.
  • Use a controlled grazing regime, ie. subdivide paddocks with electric fencing to allow pasture to lengthen.
  • The best long term control option includes pasture renewal, ideally with a summer of fodder cropping. This will germinate a large proportion of the dormant seed and allow easy control.

The Northland Regional Council is continuing investigation into biological control options.  Domesticated goats work well as a biological control.  However, nodding thistle is considered to be such a threat that eradication, rather than control, is the aim.

 

Don’t buy uncertified seed and don’t buy hay from any unknown source, particularly from the Waikato and Bay of Plenty regions.

 

Make sure any machinery entering your property has been thoroughly cleaned.

Your responsibility

Nodding thistle is a 'total control' pest plant.  This means that the occupier or owner of a property where the plant is growing must aim at completely eradicating the plant.  It is illegal to sell, propagate, or distribute any parts of this pest plant in the Northland region.

 

The long-term goal is to totally eradicate the species from Northland.  Report any sightings of nodding thistle to the Northland Regional Council.

Recommended control methods

Site management:

  • Good pasture management can prevent establishment.
  • Prevent overgrazing especially in summer.
  • Ensure biocontrol agents are present.

Recommended approaches:

  1. Grub out scattered plants or small infestations; remove at least first 5cm of taproot.
  2. Weed wipe, all year round (300ml glyphosate/1L or 1g metsulfuron/1L).
  3. Spray lightly, not to run off, spring - summer (100ml glyphosate + 20ml penetrant/10L) or winter (3g metsulfuron + 10ml penetrant/10L). Avoid water contamination.
  4. Boom spraying established infestations (2,4-D ethylhexyl ester 2-2.5l/ha).

Caution: When using any herbicide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed. 

More information

For further information or control advice please contact one of our Biosecurity Officers at the Northland Regional Council on 0800 002 004:

  • Whangarei: Ken Massey
  • Dargaville: Peter Joynt
  • Kaitaia: Doug Foster

 

Top.