Effect of mowing a legume fertility-building crop on shoot numbers of creeping thistle (Cirsium arvense (L.) Scop.)

Summary

This report was presented at the UK Organic Research 2002 Conference. Perennial weeds with spreading root systems, e.g. Cirsium arvense, are difficult to control in organic arable rotations, particularly in those without grazed leys. Competitive crops and repeated mowing are proven methods of control that can be applied to the legume fertility-building crops in stockless rotations. An experiment at ADAS Terrington in 2000 compared a standard treatment of mowing at 45 cm legume height (x4) with mowing every two weeks (x8), and mowing when thistle flower buds were visible (x3). Thistle shoot numbers counted in July 2001 were around 75% less than at start of mowing in April 2000 (mean of 9.5 shoots per m2). The results suggest that achieving and maintaining a dense competitive crop has more influence than mowing frequency on creeping thistle survival under a clover fertility-building crop.