Management of inflorescence and viable seed production of blackgrass ( Alopecurus myosuroides) on set-aside in France

Abstract

Two experiments were carried out, one in a glasshouse and the other in the field, to assess the effect of weeding management (type and date) on blackgrass seed production during set-aside. The results of the field experiment were used to establish relationships between head length and spikelet number per head. Head number per plant was not reduced by one mowing in glasshouse, but it was reduced by double mowing. Early (beginning of anthesis) or intermediate (half-anthesis) glyphosate reduced head number by 72 or 50%, respectively, compared to a control, but later (during seed ripening) application did not. A first mowing reduced the length of heads elongated after the mowing by 25% compared to a control, but less than two successive mowings (by 50%). Seed viability was greatly reduced by early glyphosate (by 91%) compared to a control, less by medium date spraying and two mowings (by 17 and 47%, respectively), and not by one mowing or late spraying. These results were checked at two densities in the field experiment. The results of head length for low density were consistent with those in glasshouse, but head number did not differ between treatments. Head number per plant and head length at the highest density were lower (from 50 to 76% according to the treatments for head number and from 3 to 16% according to the treatments for head length) than those for individual plants. These preliminary results give indications, which should be checked in farmers’ field conditions, for better control of blackgrass in set-aside fields.