This field trial at Roseworthy was undertaken to investigate factorial combinations of sowing time, seed rate and herbicides on the management of annual ryegrass in faba beans.

ARG plant density was significantly influenced by the time of sowing (P<0.001), herbicide treatment (P<0.001) and the interaction between the time of sowing and herbicide (P=0.012). The 3 week delay in seeding faba beans had no impact on ARG plant density, as shown by the similar ARG density in the simazine + trifluralin treatment. However, POST clethodim and butroxydim had much greater efficacy in the 2nd time of sowing (TOS 2) than in the TOS 1. The same trend was evident in ARG seed set when crop seeding was delayed. In the Simazine + Trifluralin (IBS) treatment there was only an 8% reduction in ARG seed production when seeding was delayed. However, Simazine + Trifluralin (IBS) fb Clethodim had a 62% reduction in ARG seed production in TOS 2 than in TOS 1. ARG seed production was also strongly influenced by faba bean seed rate (P<0.001). The high faba bean seed rate had 43% less ARG seed set compared to the low faba bean seed rate. This result indicates that faba beans can be highly competitive with ARG at the high seed rate. Faba bean grain yield was significantly influenced by crop seed rate (P<0.001), with the high seed rate yielding 14% and 30% higher than the medium and low seed rates, respectively. Herbicide treatment had a significant effect on faba bean grain yield. When POST clethodim was applied after the Simazine + Trifluralin IBS (1.55 t/ha), faba bean grain yield improved by 43% to 2.211 t/ha. Crop yield responses to herbicides treatments were consistent with their efficacy on ARG, which highlights the sensitivity of faba bean grain yield to weed competition. This study has shown that at high plant density, faba beans can provide a significant suppression of ARG. However, faba beans were very intolerant to weeds as shown by the large yield losses. Higher seed rates, are important to both increase competitiveness of faba beans in suppressing ARG, and to also maintain grain yield. However, fungal disease management would need to be monitored and managed effectively.