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Why they are pest plants
Ragwort (Senecio jacobaea), plumeless thistle (Carduus acanthoides) and nodding thistle (Carduus nutans) are highly invasive agricultural pests that have unpalatable foliage, reducing pasture production throughout New Zealand. Ragwort is poisonous to cattle and horses.
How to recognise these pest plants
Ragwort
Ragwort is easily recognised by its bright yellow flowers, which appear from November to April. The flower stem can grow up to 1.2 m tall. Each flower is approximately two centimetres across and flowers are in flat-topped clusters. Recognising the juvenile plant is more difficult. As a young plant, ragwort is a flat rosette of dark green leaves with large lobes. As the plant matures and forms a stem, the leaves become deeply cut and stalk-less, growing close to the stem.
Nodding thistle
Many nodding thistle plants are biennial, germinating in autumn and only flowering in the second summer. Nodding thistle grows like the scotch thistle but it stands taller, with branches coming from higher on the stem. In the rosette stage, the leaves are usually long and narrow (up to 18 cm long and 10 cm wide) and deeply cut with spiny edges. The upper surfaces of the leaves have a metallic sheen and appear whitish at the base of the spines. Nodding thistle can grow up to 1.6 m high. The flower head is a distinctive bright crimson colour, larger than that of a scotch thistle and droops down nodding in the wind. Flowers are about 4 cm in diameter and appear from November to February.
Plumeless thistle
Plumeless thistle is almost identical to nodding thistle in both the rosette stage and flowering stage. However, plumeless thistle's flower heads don't droop and its bracts do not curve backwards.
Responsibility for control
The landowner/occupier is responsible for control. The level of control depends on where the property is. Intensively farmed areas are 'total control' areas, while all other areas are 'boundary control'.
If your property is in a total control area, you are required to destroy all ragwort, plumeless thistle and nodding thistle plants on your property to prevent them flowering. The total control zones for ragwort and thistles are not identical. Refer to the boundary control area maps for an overview of these zones.
In boundary control areas the land occupier must destroy all ragwort, plumeless thistle and nodding thistle within 50 m of the property boundary. If you graze the roadside then you are responsible for controlling plant pests on this adjoining land.
Control areas for ragwort
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Control areas for nodding and plumeless thistle
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How to control ragwort
Physical control
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Pulling plants out and disposing of them by deeply burying, burning or composting (if no seed heads are present) is an effective method of controlling ragwort. Plants are best pulled at the flowering stage where the roots are much less likely to re-grow. Mowing ragwort is not recommended, as it will encourage the plant to become multi-crowned or to become a perennnial plant, making it difficult to control. Ragwort is poisonous to cattle and horses but not sheep, so stocking ragwort-infested areas with sheep will reduce the number of plants.
Herbicide control
There are many effective herbicides that will control ragwort. The herbicide best suited to your property will depend on the level of infestation, the application equipment you have available and the stage of growth the plants are at. Contact your local Biosecurity Plant Pest Contractor for free advice on what herbicide and application method would best suit you.
A boom/aerial application of herbicide will affect desirable species such as clover and ryegrass. This damage can be minimised by applying herbicide to ragwort plants in the seedling/rosette stage during autumn and early winter. Be aware that ragwort plants may become more palatable to cattle and horses after spraying. Stock should be removed until the treated plants die.
Small block owners who may not have access to spray equipment could consider physical control methods or select a herbicide such as Tordon® 2G which is a dry application powder and does not require mixing or spray equipment.1
How to control plumeless and nodding thistle
Physical control
Grubbing plants is an effective method of controlling thistles, provided that they are grubbed at least five cm below the crown and control work takes place before the onset of seed. Mowing (or topping) thistles is less effective as the plant is able to re-grow from the crown. You will need to mow repeatedly to make sure the plants do not reach flowering/seeding stage.
Herbicide control
There are many herbicides that will control plumeless and nodding thistle and the best herbicide for your property will depend on the level of infestation, the application equipment you have and the stage of growth the plants are at. Contact your local Biosecurity Plant Pest Contractor for free advice on what herbicide and application method best suit you.
Spot spraying plants should be done before flowering, as mature plants are less susceptible to herbicides. Spraying after seed has set is ineffective, so make sure that you do not allow plumeless or nodding thistle to go to seed. Boom spraying in autumn / early winter with a herbicide such as MCPA, Pasture-Kleen or Batton provides effective control of seedlings and reduces the likelyhood of pasture damage compared to a spring application. Because plumeless thistle germinates at a later stage it is difficult to control both plumeless and nodding thistle with one autumn / winter application.
Small block owners who may not have access to spray equipment could consider grubbing out plants or selecting a herbicide such as Tordon® 2G which is a dry application powder and does not require mixing or spray equipment. Using non-selective herbicides (you may already have purchased for other plant control jobs) will destroy surrounding pasture species and reduce competition against new thistle seedlings.
Summary of herbicides for control
When using herbicides:
- read the instructions on the manufacturer's lable closely
- always wear protective clothing
- always minimise the risk to desirable plants
- contact the supplier for further advice.
| Herbicide |
Controls ragwort |
Controls plumeless and nodding thistle |
Spot spray |
Dry application (powder) |
Carpet wiping (spring/summer) |
Boom spray |
| Escort® |
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| Pasture-Kleen™ |
small rosettes |
small rosettes |
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| Batton |
small rosettes |
small rosettes |
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| MCPA |
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small rosettes |
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| Organic Interceptor™ |
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| Prefix® -D |
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| Tordon® 2G |
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| Tordon® Gold |
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Biological control
Biological control involves importing insects or fungi that feed on plants in their native countries. Biological control agents reduce infestations but do not eradicate plants from an area. All the following bio-control agents have been released thought out the Waikato region and have established themselves in all suitable areas. If you have ragwort, plumeless or nodding thistle on your property you will still need to undertake control work.
Three agents have been released in the Waikato region to attack ragwort: cinnabar moth, ragwort flea beetle and ragwort seedfly. The ragwort flea beetle has had the most significant impact on ragwort in the region. In its larvae stage, the beetle feeds onthe crown of the ragwort plant. Ragwort flea beetle was realeased in New Zealand in 1981 and has in places reduced ragwort from 60-98 per cent of its former density.
Three agents have been released in the Waikato region to feed on nodding thistle - receptacle weevil, crown weevil and gall fly. Each of these agents will also feed on plumeless thistle. The receptacle weevil has had the most singinficant impact on ragwort in the region. The larvae feed on the receptacles, reducing the amount of seed being produced. The effect is obvious only long-term, as this agent does not reduce plant growth.
Manaaki Whenua - Landcare Research runs a national biological control programme. Waikato Regional Council supports the programme and maintains a local biological control programme for the Waikato region.
More information
For further advice contact your local biosecurity pest plant contractor on 0800 BIOSECURITY (0800 246 732).
For more information on plant pests check out the Weedbusters website.
Related publications
- Visit our Waikato Regional Pest Management Strategy.
- 'What makes a pest a pest? - A guide to Waikatos pest management future' Pick up, download or order for free from our offices.
- 'Plant me instead - Plants to use in place of common pest plants'. Pick up or order for free from our offices.
- The 'National Pest Plant Accord Manual'. Pick up or order for $10 from our offices, or view it online for free.
- 'Poisonous plants and fungi in New Zealand - A guide for parents, schools and child minders' for $15 from our offices. Pick up or order .
Disclaimer
Although this content has been prepared in good faith from a number of sources believed to be reliable, Waikato Regional Council does not give any warranty that all information contained is accurate or complete, or that advice given will be appropriate in all circumstances. Mention of product trade names implies neither endorsement of those products nor criticisms of similar products not mentioned.