Control of Cirsium arvense (L) Scop, by herbicides and mowing

Summary: The efficacy of mowing and of herbicides (applied by spot spraying or boom spraying) for the selective control of Cirsium arvense (L) Scop, in Victorian pastures was investigated. The pastures were based on Trifolium repens L. and Lolium perenne L. A general decline in the number of thistle shoots in untreated plots at three out of five sites was recorded.‘Tordon 50‐d' (5% a.i. picloram and 20% a.i. 2,4‐D as triisopropanolamine salts), MCPB, 2,4‐DB and mowing resulted in suppression, but not eradication, during the experimental period. MCPB and 2,4‐DB are the most suitable herbicides for selective control. The use of‘Tordon 50‐d' is restricted by its effect on clovers, soil persistence and cost. Variable growth of C. arvense, associated with variable summer rainfall in Victoria, increases the difficulty in controlling this weed and necessitates a persistent long term approach.