A study of populations of black‐grass ( Alopecurus myosuroides ) in winter wheat, as influenced by seed shed in the previous crop, cultivation system and straw disposal method

SUMMARY A two year experiment was conducted in winter wheat infested with black‐grass. In the first year black‐grass was either allowed to develop and shed seed freely or was completely controlled by herbicides. In the second year straw was either burnt or removed by baling and three cultivation systems were compared – ploughing, tine cultivations and direct drilling. No black‐grass herbicides were applied in the second year. The presence of seeds shed in the previous crop greatly influenced the black‐grass infestation in the direct drilled crop where it was calculated that 80–90% of plants were derived from these recently shed seeds. In the crop established after ploughing, the black‐grass infestation was unaffected by seed production in the previous crop. Tine cultivations gave results similar to those found with direct drilling. It is suggested that these differences between cultivations were due to the presence of old seeds in the soil which were brought up to the soil surface by ploughing, but not by cultivations which did not invert the soil. Straw burning destroyed many freshly shed seeds on the soil surface and resulted in less black‐grass in the crop although the effect tended to be masked by cultivations. The practical implications of the results are discussed.