This field trial was undertaken at Roseworthy in SA, a medium rainfall environment, to investigate factorial combinations of sowing time, cultivar (hybrid Vs open-pollinated), seed rate and herbicides on the management of Annual Ryegrass in triazine tolerant canola.

• There was no effect of a two-week delay in sowing (P=0.672) on in-crop ryegrass plant density with 390 plants/m2 in TOS 1 and 401 plants/m2 in TOS 2. The combination of dry autumn and high seed dormancy in this ryegrass population is likely to be the reason for the lack of sowing time effect on weed density.
• Combinations of pre- and post-emergent clethodim or clethodim + Factor failed to reduce ryegrass plant density below 200 plants/m2. Such a high level of ryegrass plant survival is likely to be related to the presence of a high level of group A/1 resistance in this population of ryegrass.
• Ryegrass seed production was significantly affected by canola sowing time (P<0.001) with TOS 1 producing 35,757 seeds/m2 as compared to 49,368 seeds/m2 in TOS 2. Greater seed production with delayed crop sowing is likely to be the result of reduced competitive ability of canola with weeds when sown later.
• Superior early crop vigour in Trophy was reflected in 21% lower ryegrass seed set than in Bonito (37536 seeds/m2 Vs 47,589 seed/m2). Canola sown at the higher seed rate (50 seeds/m2) resulted in a denser crop canola, which reduced ryegrass seed set by 38% (32,683 Vs 52,442 seeds/m2).
• Combination of early crop sowing, higher seed rate, hybrid variety and herbicide treatments allowed canola to produce more than 2 t/ha yield at this site with a high seedbank of multiple herbicide resistant ryegrass. However, ryegrass population that survived management was able to produce up to 60,000 seeds/m2. Future management of this trial paddock would require at least 3 years of effective ryegrass management before normal crop management programs can resume.