Variegated Thistle Control Guide

Do's and Don'ts of variegated thistle control

Variegated thistle flower, photo: M. Baker

Do's

  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see Herbicides for variegated thistle control for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries; and
  • Revisit and regularly inspect the site and ensure follow-up is undertaken.

Don'ts

  • Don't introduce thistles to thistle-free areas (e.g. by failing to wash down machinery and equipment between sites);
  • Don't start your control program without first planning your approach;
  • Don't allow variegated thistle to flower and set seed before treatment; and
  • Don't rely on one attempt at removal - follow-up is essential.


Spread of variegated thistle

  • Variegated thistle is spread by seed. Variegated thistle seed has only a rudimentary 'pappus' or parachute of hairs and is not spread by wind.
  • Variegated thistle seed is commonly spread in cereal seed. Seed is also spread by humans and livestock, in the fleece of sheep, on the wheels of vehicles, and by run off during heavy rain.

Avoid the introduction of variegated thistle

  • Avoid introducing variegated thistle seed into clean areas, or into areas from which the weed is being eradicated.
  • Implements and vehicles which have been used on infested areas should be thoroughly cleaned on leaving. See the Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading variegated thistle.
  • All seed, feed grains or hay should be free of variegated thistle seed.
  • Any livestock suspected of carrying seed on their bodies or in their digestive system should be held in a suitable area for approximately two weeks before being put on clean paddocks.
  • Special care should be exercised when buying sheep from other properties as seed is readily carried in wool.

Physical removal

  • Individual plants and small patches can be removed using hand-hoeing. Ensure that the growing point and the top 20 to 40 mm of the taproot are removed.

Cultivation

  • Variegated thistle does not readily invade healthy and vigorous pasture, and seedlings establish mainly when pasture opens up due to over-grazing or insect damage.
  • Aim to maintain a vigorous pasture. Heavily infested areas may need to be re-sown with perennial pasture grasses.

Chemical control

  • A number of herbicides are registered for use on variegated thistle in Tasmania. See Herbicides for Variegated Thistle Control for more information.
  • To avoid poisoning, stock should be removed from infested areas before any herbicide application and kept off the area until the thistles are completely dead. This may take 2-3 weeks after spraying.
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