The influence of tillage and method of straw disposal on the survival and growth of black‐grass, Alopecurus myosuroides, and its control by chlortoluron and isoproturon

SUMMARY A winter wheat crop was established in a field infested with black‐grass. Three cultivation systems were used ‐ ploughing, tine cultivation and direct drilling. Straw of the previous wheat crop was either spread and burnt or removed by baling. Chlortoluron at 1–60 and 3–20 kg/ha pre‐emergence and isoproturon at 1 14 and 2–27 kg/ha pre‐ and post‐emergence were applied to sub‐plots of all cultivated treatments. Ploughing substantially reduced black‐grass infestation compared with the other two cultivations. Straw burning was effective in destroying many seeds and resulted in less black‐grass in the crop. The pre‐emergence herbicide applications were more effective after ploughing than after direct drilling, irrespective of straw disposal method. When the straw was burnt, black‐grass control on the tine cultivated plots was at least as good as after ploughing but where the straw was baled, poorer control was obtained. Chlortoluron gave better control than isoproturon but the relative effects of cultivations and straw disposal method were similar with both herbicides. The post‐emergence herbicide treatments gave excellent control after all cultivations. Many black‐grass seeds in the surface soil were shown to remain dormant, but viable, from autumn until the following April.