Variegated Thistle Silybum marianum
Origin. Eurasia.
Distribution in Canberra Region. CNP: patches found in most areas, especially under trees and in more moist areas.
CUPP areas: less. Farms: some heavily infested.
Dispersal. Mostly local from seeds dropping; windblown for short distances or carried downhill by rain. Mostly carried by livestock, and found in old sheep camps, under trees where livestock congregate.
General description and biology
An annual stout-stemmed erect weed, to 2 m in height and 5 cm diameter at base.
Leaves large, mottled, shiny green with white veins and spiny margins; stem-clasping.
Flowers (Nov.-Dec.) light purple, on tips of branches, surrounded by spiky bracts.
Thrives in more moist and fertile conditions, either shady or exposed.
Commonly occur in large clumps under large trees, and on former �sheep camps�.
Control methods
a. Manual methods
Best cut with loppers/giant secateurs, or dug out with mattock; or small ones pulled out.
If cut at ground level (below the first leaves) they don�t usually grow again.
The stems of all but small ones are too tough for brushcutters with nylon blades.
The rosettes can be quite easily cut off just below ground level with a mattock or mini-pick; less easily, with loppers. Getting them at the rosette stage is really the best strategy.
Chipping out with mattock is better, to avoid occasional regrowth.
If already gone to seed, it is useful and effective to collect and compost seedheads.
Best is a combination of chipping out rosettes + bagging any seedheads still around from last crop.
b. Chemical methods
Similar to those described for saffron thistles. However as the rosettes are much larger it is not necessary that the grass be cut or grazed before spraying � in spring.
Contact CNP/CUPP for advice on the chemical.
Alternative: dab glyphosate (1:2) copiously on the centre of rosette, using spraybottle or weed-brush.