Estimation of seed production by Myosotis arvensis, Veronica hederifolia and Viola arvensis under different competitive conditions

Seed production by Myosotis arvensis, Viola arvensis, Veronica persica and Veronica hederifolia was estimated in a series of 12 experiments. These species were grown in the field either on their own or in competition with a range of arable crops, though mainly winter wheat. Plants were harvested in summer, as they approached maturity and capsule and flower head numbers and dry weights were recorded. Seeds produced by each capsule (flower head) were also assessed in all experiments. Seed numbers were regressed with plant weight on a log/log basis, and high correlations were achieved in all cases (percentage variance accounted for > 91%). Slopes of the overall regression lines were slightly < 1.0 for all species (0.77-0.92). In the absence of crop competition, M. arvensis was estimated to produce c. 100 000, V. arvensis 3714, V. persica 4100 and V. hederifolia 980 seeds per plant. Competition from winter wheat reduced seed production of three of the species by more than 70%, but only reduced V. hederifolia production by 56%. These data on seed production form a key building block for the construction of population dynamics models to predict the likely consequences of the lower input weed management that is being promoted to reduce the environmental impact of weed control.