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Creeping thistle

( Cirsium arvense )
Canada Thistle

Perennial weed found in grassland and perennial crops like orchards, spreading by deep, white, fleshy roots and by seed. There are male and female plants (dioecious), the former having spherical flowers and the latter elongated. They need to be within 100m of each other for pollination to occur. When ripe the seeds are wind-borne on fluffy balls of long hairs and germinate the same year or the following spring. The flowering stem dies back when the seeds mature, but remains upright to disperse them.
The seedling develops a long tap root which can go down about 3 metres and lateral roots which can spread for up to 6 metres. These lateral roots develop adventitious buds which grow in the spring.
It is proscribed under the Weeds Act 1959 and must be controlled in agricultural land. Allowing the seed to disperse is an offence.

Flowers - purple from July to September, turning white as the seeds mature
Height - up to 100cm.

CREEPING THISTLE

Remove the young plants before they can develop a perennial root system. For established plants, dig out as much root as possible, repeat many times. Breaking up the roots can result in multiplying the problem, unless they are brought to the surface where drying or frost will kill them. Also the roots can lie dormant in the ground for many years.
Weedkillers to use:-
Glyphosate, systemic action, taken down into underground parts.
Dichlobenil applied in early spring, kills emerging shoots for up to a year among established woody plants.

The Spear Thistle is a larger plant with more vicious spines, but does not have creeping roots, and is similarly controlled by the Weeds Act.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.

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