Nodding Thistle

(Carduus nutans)

Boundary Control Pest

Nodding Thistle is an annual or biennial plant, with erect flowering stems up to 1.5 metres tall. It has large purple flowers that droop when mature. Most seeds fall close to the parent plant, being large and heavy. The seeds can also be spread by water, animals, hay, agricultural equipment and in agricultural seed. They will mature even after plants are cut, and have a longevity of 10 years.

Reasons for the Strategy
Several clumps of green stalks with purple flowers on top.

Nodding Thistle is considered to be the most aggressive thistle in New Zealand. Its suppression of pasture has the potential to reduce grazing capacity – it is capable of total ground cover. It will quickly spread to uninfested areas as a consequence of summer drought. Dense mature stands obstruct livestock movement and provide habitat for rabbits and vermin. Spines adhere to wool, lowering its value.

Nodding Thistle is assessed at “6” on the infestation curve. It is widespread throughout the Tasman-Nelson region, except for Murchison and most of Golden Bay. The distribution of Nodding Thistle has reached a level where the most cost effective form of control is to require boundary control, and to invest in biocontrol. This will assist in protecting land that is clear, or being cleared of Nodding Thistle, from invasion from adjacent land by Nodding Thistle. Extensive areas of suitable habitat, and the potential for it to cause significant adverse effects, mean the benefits of boundary control far outweigh the costs.

Objective

To control the spread of Nodding Thistle from adjacent properties to land that is clear, or being cleared of Nodding Thistle, in the Tasman-Nelson region during the term of the Strategy.

Alternative Measures

The alternative option of “do nothing” or relying on voluntary control will not achieve the objective of the prevention of the spread of Nodding Thistle to adjacent properties where there is no Nodding Thistle, or where control is being carried out. Requiring a greater level of control, instead of just boundary control, is not appropriate given the widespread distribution of Nodding Thistle, and that the occupier is the main beneficiary.

Strategy Rule for Nodding Thistle

The occupier shall destroy all adult and juvenile forms of Nodding Thistle located 20 metres or less from the boundary of the land that they occupy where the adjacent property is clear, or being cleared of Nodding Thistle. A breach of Strategy Rule 7.7.5 is an offence under Section 154(r) of the Biosecurity Act 1993.

Explanation of Strategy Rule

The Management Agency will limit its intervention to enforce compliance of the rule to occasions when a reasonable complaint is received from an adjoining land occupier. This would require the complainant’s land to be already clear, or being cleared of Nodding Thistle, and that any invasion of the pest plant through the boundary has the potential to cause economic harm to the complainant’s land.

Biosecurity Act Requirement

No person shall knowingly sell, propagate, breed, release, or commercially display Nodding Thistle, under Sections 52 and 53 of the Act.