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Weed of the month: Scotch Thistle

Scotch Thistle grows in all areas of Putty. Dense stands of mature thistles create barriers that hinder livestock movement. They compete with pastures, reduce carrying capacity and can cause injury to livestock and people handling the livestock. Dense thistle populations can also reduce property values.Ā 

Thistles are prolific seeders and can spread quickly.  Once established, they are difficult to control.  Seeds can germinate at any time of year however rain in summer and autumn can bring on growth.  Seedling survival is highest when grass cover is sparse due to a previous season of poor rainfall.  

Controlling an infestation.

Isolated plants should be removed using a hoe or mattock, removing as much of the taproot as possible so that regrowth does not occur.  Cultivation is effective on seedlings or young rosettes if they are uprooted. Slashing or mowing is not usually effective as plants develop new growth from the base and seed heads that are cut and left lying on the ground can germinate.

Herbicide control can be very effective and is an essential part of the overall management of these thistles. For large stand of thistles, spraying is the best way to get rid of them.

Effective herbicides are GrazonĀ® or a generic product that contains 300 g/l of Triclopyr and 100g/l of Picloram.  You could also use Dicamba that contains 340g/l MCPA and 80g/l of Dicamba or Melsulfuron 600. These three are selective herbicides and will not kill your grass nearby. Glyphosate will also be effective but keep in mind that Glyphosate will kill everything it comes in contact with.  Metsulfuron 600 is available at $25 per 500 gram container from Three Valleys Landcare.  .Contact Ken Ferguson on 65797077.


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