Spear thistle (Cirsium vulgare)
Spear thistle occurs widely on lowland and upland grassland and waste places. The weed competes effectively with crops for water, light and nutrients. It is biennial and only spreads by seed. Mature plants are normally 30-50 cm tall, with flowers from July through to late autumn. Large numbers of seeds are produced which can be blown by wind across farm and field boundaries.
The plants can be cut each year before mid-July to prevent shedding of viable seed. It is also possible to remove them by digging. Long-term control is possible from herbicide treatment; spear thistle is susceptible to clopyralid and moderately susceptible to MCPA herbicides. Where clover is an important constituent of the sward, a mixture of MCPA and MCPB herbicides is more appropriate.