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Nodding thistle is a biennial plant that grows from over-wintering rosettes and has a long, fleshy taproot. The flowering stems grow up to 1.5m tall bearing red-purple or, occasionally, white flowers that droop or nod when mature. Sharp spines densely cover the stems and leaf margins.
Nodding thistle is predominantly a weed of pasture (particularly pasture grazed by sheep) and also invades roadsides, wasteland and crops such as lucerne. It will grow in most soil types but does not grow well in excessively wet, dry, or shady conditions and does best under higher soil fertility.
Nodding thistle is considered to be the most aggressive thistle in New Zealand. It can invade pastures at all stages of development, particularly those grazed by sheep, and quickly establish in pastures suffering from summer drought. Its main economic impact is that it prevents stock from eating plants growing in the vicinity of the thistle, replaces desirable vegetation and hinders stock movement.
Nodding thistle is a prolific seeder, with approximately 200 seeds are produced per flower, of which two-thirds are viable. Seed may lay dormant in the soil for up to 20 years.
Good pasture management can prevent establishment.
•Prevent overgrazing especially in summer.
•Ensure biocontrol agents are present.
For further information or control advice please contact one of our Biosecurity Officers at the Northland Regional Council on 0800 002 004.