Two experiments have investigated the persistence of 16 arable, annual broad-leaved weed species over 6 years in a silty loam and a clay soil. Small plastic beads were included as an 'inert' comparison. Seeds were broadcast in October on to plots at the start of the experiment, and these were either tine cultivated or ploughed annually thereafter. Plots were sown with either spring or winter wheat. As far as possible, weed seeding was prevented each year. For some species, the seed decline appeared to be slower on the ploughed plots than on the tined plots and in the winter wheat compared with the spring wheat. Seed decline also tended to be slower on the clay soil at Rothamsted than on the silty loam at Long Ashton. Some species declined rapidly (e.g. Brassica napus , Chrysanthemum segetum , Galium aparine , Galeopsis tetrahit ), with annual decline rates in excess of 58%, whereas others declined very little (e.g. Papaver rhoeas decline rate 9%). Most of the other species had decline rates between 20% and 40%. The results are discussed in relation to the development of population dynamics models to predict long-term consequences of alternative weed management strategies.

Summary.Plant‐parasitic nematodes were monitored in the multidisciplinary TALISMAN (Towards a Lower Input System Minimising Agrochemicals and Nitrogen) experiment undertaken at ADAS experimental sites at Boxworth, Drayton and High Mowthorpe, England (1990–1994). The treatments compared standard and alternative rotations, reduced and full herbicide application and full and half rate nitrogen at all three sites. After 6 yr, results snowed no evidence of either a positive or negative impact of the reduced application of agrochemicals on the non‐target plant‐parasitic nematode populations. Greatest differences were the unexplained year to year variability in nematode numbers.

There is increasing interest in policies encouraging organic or biological farming. Farmers in the UK are not converting to organic farming in large numbers, with one principal reason being the problem of weed control. There is some evidence that weed problems reduce over time, but it is uncertain to what degree weed populations increase during conversion at the field rather than plot scale and how management strategies affect that increase. The results of surveying two farms in conversion over 4 seasons suggest weed populations increase rapidly, but there is evidence on one farm with fields in longer conversion periods that the weed population growth stabilises. However, periods of grass ley of greater than two seasons duration greatly reduce weed population growth during the conversion period. There is no evidence of an increase in weed species number during the conversion period.