Nodding Thistle Control Guide

Do's and Don'ts of nodding thistle control

Nodding thistle flowering plant

Do's

  • Plan your control program, this will save time and money in the long-run.
  • Use cultivation to eradicate a mature nodding thistle infestation.
  • Follow up cultivation by treating any nodding thistles that germinate in the crop.
  • Carefully time your use of herbicide for best results (see Herbicides for Nodding Thistle Control for more information).

Don'ts

  • Don't start your control program without first planning your approach.
  • Don't rely on just cutting and slashing - thistles will re-sprout from cut stems and rootstock.

Spread of nodding thistle

  • Seed is the only means of spread. A single plant has up to 120,000 seeds.
  • Seed may be carried as a contaminant of produce seed and hay, on vehicles and machinery, and in water and soil. Wind does not have a major role in dispersal and nodding thistle seed are usually not blown more than 10 metres.

Physical removal
  • Slashing and cutting of plants at the bud or early flowering stage can be used to delay flowering or seeding. However, this will usually cause 'coppicing' from the stem or rootstock, and must be followed up by measures to kill the whole plant.
  • Where the number of plants involved is small, removal by grubbing is feasible. The thistle should be grubbed out to a depth of at least 5 cm.
  • If the plant is in full flower, heads should be collected and burnt since seed may mature on the cut stalks.

Cultivation

  • Control of nodding thistle is best achieved by adequate cultivation of the site.
  • Ploughing and preparation for a crop will remove the germinated thistles, leaving a reserve of seed in the soil, which may germinate to produce thistles which will need to be dealt with in the crop.
  • Nodding thistle seed can remain dormant in the soil for 10 years or more. This dormant seed may germinate as a result of cultivation.

Biological control

  • Biological control is the use of living species, usually an insect, mite or disease, to control a weed.
  • Three biological control agents have been trialed or released in Tasmania to help control nodding thistle: the thistle-head weevil, seed-fly, and rosette weevil.
  • For more information on biological control programs in Tasmania contact the Tasmanian Institute of Agriculture.

Chemical control

  • A number of herbicides are registered for use on nodding thistle in Tasmania (see Herbicides for Nodding Thistle Control for more information).
  • An infestation may contain plants at various stages, including seedlings, small rosettes, large rosettes, flower-stem growth, and full flower. The type of herbicide used will depend on the stages of growth in an infestation (see Herbicides for Nodding Thistle Control for more information).
  • The best time to spray nodding thistle is when the plant is in the seedling and small rosette stage.
  • Control of an infestation in pasture may require spraying in spring and autumn.
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