Nodding Thistle (Carduus nutans)

The paddock and roadside nasties are taking advantage of the advance of more spring like weather, and the base rosettes of several types of thistle are already appearing, particularly in bare spots.  So now is the time to attack before they shoot upwards.

Nodding thistle is a largely biennial plant, very invasive into pasture, and can form dense stands which obstruct livestock movement and suppress the growth of useful and palatable plants.  Where the perhaps better known Scotch thistle begins with a rosette of leaves covered on the top side and edges with small hairy prickles, at the rosette stage Nodding thistle leaves are about 18 cm long and 10 cm wide, deeply divided into triangular lobes with firm spiny tips up to 8mm long.  An antagonistic plant right from the start.  Once it grows upwards the flower stalks can be 75 cm or more tall with many stems growing from the basal rosette.

The common name derives from the fact that the solitary red-purple flower heads droop down at the tip when mature, where those of other types remain vertical.  Flower heads can be 4 cm in diameter, surrounded by two sets of bracts, with the outer ring curved backwards and the inner standing erect.  Flowering from November to February each flower produces a mass of small seeds, each equipped with a pappus or flying mechanism to ensure rapid spread.

Found in New Zealand since the 1930’s, herbicide resistant strains developed during the 1980s.  It originated from Europe, north-west Africa and Asia Minor, and is found now throughout New Zealand, although more in dry parts and less in Westland.  They are subject to Pest Plant Management Strategies in many regions.  For instance Environment Waikato requires ‘total control’ by the occupier on all land from Hamilton to Tokoroa and Port Waikato, including Coromandel, and control within 50 metres of the boundary ‘boundary control’ in all other areas under its jurisdiction (map on its website).

What to use to control nodding thistles varies depending on which stage of growth they are at, and whether those in your area are phenoxy-resistant.  While MCPB will work on seedlings without damaging pasture, once they grow larger MCPA or 2,4-D is required, and even these will not work on resistant types without the addition of clopyralid which will cause even greater damage to clover and other pasture.  Massey University’s weed database recommends that if there are only a few plants then grubbing with a hoe to chop the taproot 2-3 cm below ground level is the most effective.  Just removing the rosette will not kill the plant and it will re-grow from the crown.

Otherwise, if you have a goat or two, they are happy to eat the plants once they grow taller than the surrounding vegetation.

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