Keep nodding and plumeless thistle from affecting nearby land.
|Production threat||Environmental threat||Public threat|
Nodding and plumeless thistle are agricultural pests in the Waikato region. They are highly invasive pests and have unpalatable foliage, reducing pasture production throughout New Zealand. Seeds remain viable in the soil for many years. Their dense stands obstruct livestock movement and inhibit and suppress the growth of desirable pasture species. ‘Tufted’ seeds are spread between properties mainly by contaminated hay and machinery, uncertified seed and stock feed and also through wind dispersal.
Variegated thistle (Silybum marianum). This is a very conspicuous spiny thistle up to 2m high, which is easily recognised by cream marks on its leaves (hence the ‘variegated’ appearance). The Regional Pest Management Plan objective for the Waikato is to eradicate variegated thistle.
All landowners/occupiers in the Waikato are responsible for controlling nodding and plumeless thistle on their properties and are required to work with Waikato Regional Council in areas where control programmes are in place. If you graze the roadside then you are responsible for controlling these plant pests on that adjoining land. The level of control depends on where the property is.
See the map below for an overview of the locations of the two types of control zone.
Nodding and plumeless thistle are also banned from being sold, propagated, distributed or included in commercial displays.
The best returns from thistle control come from managing the most productive land. Relatively low returns for sheep and beef make thistle control marginal in hill country, except after a drought. High livestock value and gross margins increase the value of the pasture and make weed control more worthwhile.
Many principles which apply to nodding thistle and variegated thistles are also relevant for other thistles such as Scotch and winged thistles.
Some options for managing thistles are included below, but there are many others. For more information contact your herbicide representative or check www.pestweb.co.nz(external link).
Grubbing plants is an effective method of controlling thistles, provided that they are grubbed at least 5cm 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 regrow from the crown. You will need to mow repeatedly to make sure the plants do not reach flowering/seeding stage.
There are many herbicides that will control nodding and plumeless thistle. 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. Some suggested herbicides are included in the table in this factsheet. Contact your local biosecurity plant pest officer for free advice on what herbicide and application method would best suit your situation on the freephone 0800 BIOSEC (0800 246 732).
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 nodding or plumeless thistle to go to seed. Boom spraying in autumn and early winter with a herbicide such as MCPA, 2,4-D or Batton provides effective control of seedlings and reduces the likelihood 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 (see ‘physical
control’ above) or selecting a herbicide such as picloram granules. Picloram is a dry application powder which does not require mixing or spray equipment.
Note: using non-selective herbicides (which you may have already purchased for other plant control jobs) will destroy surrounding pasture species and reduce competition against new thistle seedlings.
Many nodding and plumeless 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, growing up to 1.6m high, with larger flowers and its leaves branching from higher on the stem. Plumeless thistle grows taller than nodding thistle – to about 2m high.
Disclaimer: Any product names mentioned below are not an endorsement nor are they a criticism of similar products not mentioned.
Summary of herbicides and application methods for control
When to apply
|2,4-D||Up to small rosette||Slight||No||Slight|
|Dicamba||Up to large rosette||Severe||No||Severe|
|Triclopyr/picloram||Up to large rosette||Yes||No||Severe|
|Metsulfuron-methyl||Up to large rosette||Yes||Usually moderate||Severe|
|Picloram||Up to large rosette||Yes||No||Severe|
|MCPA||Up to small rosette||Moderate||No||Slight|
|Glyphosate||Any stage||No||Severe||Severe but temporary|
|Clopyralid||Up to large rosette||Severe||No||Moderate-severe|
|Mecoprop/dichloroprop/MCPA||Up to small rosette||Moderate||No||Severe|
|Herbicide rules will apply. You may need to notify neighbours if spraying. The Waikato Regional Plan explains the agrichemical (herbicides) use rule in section 6.2|
After initial control, it’s important to clean out the site again at least annually to control regrowth.
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 biocontrol agents have been released throughout the Waikato and have established themselves in all suitable areas. However, if you have nodding or plumeless thistle on your property you will still need to undertake control work.
Four biological agents have been released in the Waikato to feed on nodding thistle:
Each of these agents will also feed on plumeless thistle. The receptacle weevil has had the most significant impact on nodding thistle 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.
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.
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