Variegated thistle
| Botanical Name | Silybum marianum |
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| Family | Asteraceae |
| Origin | Mediterranean, SW Europe |
Identification
Variegated thistle is an erect annual or biennial thistle growing up to 2.5 metres high, and 2 metres wide, which reproduces by seed. Growing from a stout taproot, the easily distinguished rosette leaves are somewhat shiny and "variegated" in appearance due to the prominent white veins and blotches. The deeply divided, spiny leaves can grown to 600mm in length. Flowering stems are stout, hollow and are much branched from the base. The large purple flowers are surrounded by many sharp spines and produce 50 to 200 black or brown seeds. Each seed is 6 to 8mm long and has a large group of downy hairs (each about 20mm long) at one end.Habitats
Variegated thistle grows best on areas of high fertility such as alluvial flats, sheep camps, stock yards and other areas of high soil nitrogen levels.Impact to Biota and Ecosystems
Variegated thistle is a large and very competitive thistle, which when well established eliminates most other plants by shading and through competition for moisture and nutrients. It invades large areas of pasture and is generally unpalatable to stock, resulting in a drastic reduction in stock carrying capacity. Dense clumps of variegated thistles also provide an ideal harbour for rabbits which in return, provide suitable conditions for the establishment of the weed by disturbing the soil.Dispersal Routes, Vectors, Infestation Sources
Seed is the only means of spread, however the distance the heavy parachute seeds can travel in the wind is not known, although most dispersal is probably within 10 metres of the plant. Seed can be spread in hay, by water, in mud, agricultural produce and grain as well as on machinery or animals.Management
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Management |
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| Physical Control |
Small patches can be grubbed out before the plants flower. |
| Disposal |
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| Chemical Control |
Larger infestations can be sprayed with one of the following herbicides. Tordon Gold 100mls per 10 litres water (knapsack) 500mls per 100 litres water (gun spray) Metsulfuron : 1 gram per 10 litres water (knapsack) 5 grams per 100 litres water (guns pray) Graze the area before spraying to reduce clover leaf and to expose the weeds to the spray. Leave for one week to allow weeds to freshen prior to spraying. Delay grazing the sprayed pasture for two weeks as treated weeds are palatable to stock. Boom spraying herbicides 2,4-D 1.5 to 2 litres per hectare (seedlings only) MCPA 3 to 4 litres per hectare (seedlings only) For further information and more detailed control methods please refer to Environment Bay of Plenty's Fact Sheet on Varigated Thistle. |
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Biological Control |
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| Recommended Approach | |
Further Comment
This native of south-west Europe has spread throughout temperate areas of the world and was first recorded as a weed in New Zealand in 1869. It is found in the Bay of Plenty region but is not as widespread as some of the other thistle species.
For further information and more detailed control methods please refer to Environment Bay of Plenty's Fact Sheet on Varigated Thistle.
This plant is prohibited from propagation, sale and distribution in the Bay of Plenty!