To investigate factorial combinations of sowing time, seed rate and herbicides on the management of brome grass in faba beans.

A field trial was undertaken at Riverton in 2020 to investigate combinations of faba bean sowing time, seed rate and herbicide treatments to control brome grass. Three week delay in sowing caused a 95% reduction in brome grass plant density in faba beans. Riverton population of brome grass has been shown by our previous research to have a low level of seed dormancy. It appears excellent rainfall at the site in April and good follow-up rains were highly suitable for stimulating seedling emergence from the seedbank. The general trend of lower brome plant density in TOS 2 than in TOS 1 was also reflected in brome panicle density, which is the major driver of its seed production. This trend was particularly clear where only pre-emergent herbicides were used for weed control. The application of Verdict® eliminated brome panicle production and seed set. There was a significant effect of faba bean seed rate (crop density) on brome grass seed production. Increasing competition from faba beans reduced brome grass seed set by more than 50% as crop seed rate increased from 20 to 40 seeds/m2. Faba bean grain yield was only influenced by the main factors time of sowing (P<0.001), seed rate (P<0.001) and herbicide treatments (P=0.007). Earlier sown faba bean produced significantly greater yield than the crop sown 3 weeks later. Faba bean seed rate also resulted in a significant increase in grain yield as seed rate increased from 20 to 40 seeds/m2. As a result of the low brome grass density at the site, the increase in grain yield in response to weed control were small but significant (P=0.007). The combination of pre-emergent propyzamide followed by post-emergent application of Verdict significantly increased faba bean yield compared to pre-emergent propyzamide alone.