Estimation of seed production by Stellaria media, Sinapis arvensis and Tripleurospermum inodorum in arable crops

Seed production by Sinapis arvensis , Tripleurospermum inodorum and Stellaria media growing alone or in crops of spring wheat, spring field beans and spring linseed was studied in 11 experiments. Seed numbers for S. arvensis and T. inodorum were measured directly from samples harvested in late summer but for S. media were estimated from measurements of flower number and seeds/flower. Seed numbers were regressed against plant dry matter. In general, a linear log/log plot (y = mx + c) fitted the data for each species quite well (R-2 = 0.75, 0.89, 0.89 for S. arvensis , T. inodorum and S. media respectively), but there were small differences between crops and years in the individual regression lines, especially the intercept values. Estimated seed production for a 'mean' 10-g plant (dry matter) in the three crops for S. arvensis, T. inodorum and S. media was 590, 6300 and 8600, respectively. Seed production tended to be lower for the weeds in wheat than it was in field beans and linseed, or in the plants grown alone, primarily due to the differences in plant weight arising from the differing competition exerted by the crops involved.