A field trial was undertaken at Minnipa in 2020 to investigate combinations of wheat seed rate and herbicide treatments to control annual ryegrass. The average seedbank of annual ryegrass (ARG) at the site was 2012 ± 461 seeds/m2. ARG plant density was significantly influenced by herbicide treatment (P=0.008). Boxer Gold and Sakura + Avadex controlled ARG plant density by 63% and 70% respectively. Consistent with the trends observed for ARG spike density, ARG seed production was also significantly influenced by herbicide treatments (P<0.001) and while not significant there was a trend towards suppression of ARG seed production when wheat seed rate was increased (P=0.096). When averaged across all the seed rate treatments, the untreated control produced 13,155 ARG seeds/m2. The Boxer Gold treatment reduced ARG seed set by 69% to 4,018 ARG seeds/m2, while the Sakura + Avadex treatment reduced it by 70% to 3,849 ARG seeds/m2. Such high ARG seed set even when using pre-emergent herbicides highlights the importance of an integrated weed management strategy that incorporates diverse crop options such as hay and includes other cultural methods such as harvest weed seed collection and improved crop competitiveness. Consistent with the level of ARG control, herbicide treatments had a significant effect on wheat grain yield with Boxer Gold (1.869 t/ha) and Sakura + Avadex (1.871 t/ha) both increasing grain yield by 35% compared to the control (1.384 t/ha).

• 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.

A field trial was undertaken in 2020 to investigate the effects of sowing time, canola variety, seed rate and herbicides on annual ryegrass management at a high rainfall site in Victoria (Winchelsea). Crop establishment at this trial site was significantly influenced by the time of sowing (P=0.006) and the seed rate (P<0.001) and there was an interaction between time of sowing and seed rate (P=0.014). Crop establishment was close to half of the target density, which may have been due to dry soil conditions in TOS 1 but there may also have been some slug damage. Select and Factor herbicides provided a much higher level of ARG control in TOS 2 than in TOS 1. Evaluation of weather data for the site showed that there were 4 frost events before the application of POST herbicides on 12 June in TOS 1, including the day of herbicide application. Previous research has shown a negative effect of frost on the level of weed control provided by these herbicides. Grain yield of canola was significantly influenced by sowing time (P=0.008), variety (P<0.001), seed rate (P<0.001) and herbicide (P<0.001). There were also significant interactions between time of sowing x variety (P=0.023), sowing time x seed rate (P<0.001) and sowing time x herbicide (P<0.001). Lower grain yield in TOS 1 compared to TOS 2 (2.3 Vs 3.4 t/ha) is most likely related to significantly lower canola plant density. The average grain yield of hybrid Ignite (3.13 t/ha) was significantly greater than that of open pollinated Wahoo (2.54 t/ha). There was a strong correlation between annual ryegrass spike density from herbicide treatments and canola grain yield (R2=0.96). Sowing time x herbicide treatments that provided weaker control of ARG also produced lower grain yield and vice versa. These results show that ARG can be highly competitive with canola in high rainfall environments and all efforts need to be made to achieve good crop establishment and selection of effective herbicide strategies.

A field trial was undertaken at Kinnabulla (VIC) in 2019 to investigate combinations of sowing time, seed rate and herbicide treatments to control brome grass in barley. Spartacus CL barley was used in this trial to enable the use of Intervix® for post-emergence control of brome grass. In 2019, the trial site received 181 mm rainfall during the growing season (April-October), which was 23% lower than the long-term average for the site. However in December 2018, the site received a heavy downpour of 199 mm, which created good growing conditions for barley crop grown in 2019. In this trial, barley seeding rate did not have a significant effect on either yield (P=0.213), brome panicles/m2 at maturity (P=0.889) or brome seed set/m2 (P=0.409). This lack of effect of crop seed rate on the number of brome panicles and seed set could be related to the high plant available water during the crop and weed life-cycle or due to Spartacus being a less competitive barley cultivar due to its erect architecture. Time of sowing had a significant effect on brome panicles/m2 at maturity and brome seed set/m2. TOS 2 had a lower brome panicle density at maturity than TOS 1 across all herbicide strategies, which was most likely due to low pre-sowing weed kill in TOS 1 as brome grass had not yet germinated. However, brome population that had germinated after the opening rains was killed by glyphosate application prior to seeding barley in TOS 2. As the numbers of panicles were lower in TOS 2, brome seed set was also reduced in TOS2 relative to TOS 1. Herbicide strategy had a significant effect on barley grain yield. As the herbicides reduced the impact of brome on barley, its yield increased from 3.24 t/ha in the knockdown treatment (NIL), to 3.72 t/ha in the pre-emergent herbicides only and to 3.96 t/ha when the pre-emergent herbicides were followed by post-emergent Intervix. Somewhat surprisingly, TOS 2 produced higher yields than TOS 1 across all the treatments, with the greatest difference being 0.46 t/ha in the Nil herbicide treatments. However, the yield difference between the two times of sowing decreased when more effective herbicides were used (0.08t/ha difference between TOS 1 and 2 in pre-emergent only and 0.04t/ha difference when pre-emergent herbicides followed by Intervix). Higher barley grain yield in the later sown crop is most likely due to a significantly greater weed density in barley in TOS 1 than in TOS 2, as large numbers of early germinating brome plants were controlled with glyphosate knockdown in TOS 2. TOS 1 also experienced a mild frost during flowering, resulting in patchy frost damage. Furthermore, May 23 (TOS 2) sowing date still falls within the optimum sowing window for Spartacus, which is an early maturity variety, and TOS 1 on April 29 was earlier than optimum for this variety.

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.

• Delay in crop sowing by 25 days did not have a significant (P=0.796) effect on brome grass density in wheat (TOS1 = 8.7 brome plants/m2 Vs 8.1 plants/m2 in TOS2). Lack of brome grass establishment during the time gap between TOS1 and 2 is likely to be related to below average rainfall (15.6 mm) during the month of May, which was less than half of the long-term average.
• Brome grass plant density in wheat was only significantly influenced by the herbicide treatments (P<0.001). Intervix alone and as a follow-up treatment after Trifluralin + Avadex provided significantly greater control of brome grass than the knockdown treatment as well as Rexade treatment.
• Even at this low weed density site, sole reliance on the knockdown herbicide treatment allowed brome to set 1753 seeds/m2 and build-up its seedbank. Application of Rexade reduced brome seed set by 84% compared to the knockdown control. Treatment with Intervix virtually eliminated weed seed set and could play an important role in brome grass management in the Mallee.
• Even though the difference in wheat grain yield between the worst (knockdown only) and the best herbicide treatment (Intervix) was 190 kg/ha, these differences (11%) were statistically significant. Based on 2021 wheat grain prices, effective brome control treatments increased revenue by about $70-80/ha.

• Brome grass panicle density was significantly influenced by the time of sowing of wheat (P=0.034) and herbicide treatments (P<0.001). Three week delay in sowing reduced brome grass panicles from 538 panicles/m2 in TOS 1 to 321 panicles/m2 in TOS 2 (40% reduction).
• The trends observed in brome grass panicle density were reflected in its seed production. The delay in crop sowing resulted in 21% reduction in brome seed set with 7392 seeds/m2 in TOS 1 as compared to 5807 seeds/m2 in TOS 2 (P=0.025). Rexade provided significantly better seed set reduction (62%) in brome than Trifluralin + Avadex Xtra but was inferior to the Intervix treatments (91-94% reduction).
• Three week delay in sowing at this site resulted in 29% higher wheat grain yield in TOS 2 (2.198 t/ha) than in TOS 1 (1.703 t/ha). This improvement in wheat yield by delayed crop sowing was associated with 84% reduction in brome plant density in TOS 2 compared to TOS 1.
• Trifluralin + Avadex Xtra, used in this trial as the control, produced 1.439 t/ha wheat yield, which was a reflection of its low efficacy against brome grass. Rexade, which only had a moderate efficacy on brome, increased wheat grain yield by 45% compared to Trifluralin + Avadex Xtra. The highest wheat yield and the lowest weed seed set in this trial was observed where Intervix post-emergent was used after pre-emergent application of Trifluralin + Avadex Xtra (2.214 t/ha).

• Ryegrass plant density in this trial was significantly affected by the herbicide treatments (P=0.002). Boxer Gold IBS had the highest ryegrass plant density, which was significantly greater than the tank-mix application of Boxer Gold with Treflan or Overwatch followed by early post-emergent Boxer Gold.
• The results obtained for ryegrass head or spike density highlight the capacity of this weed species to take advantage of cold and wet conditions. In this trial each ryegrass plant produced around 10 heads, which could cause a sizable build-up in ryegrass seedbank for subsequent crops.
• Addition of Treflan to Boxer Gold and sequential application of Boxer Gold after Overwatch caused a significant reduction in ryegrass spikes as compared to application of Boxer Gold or Overwatch by itself.
• Even though the effects of crop sowing on barley grain yield were small, the difference between TOS 2 (10.6 t/ha) and TOS 1 (10.1 t/ha) was statistically significant (P=0.03). Boxer Gold + Treflan mixture and sequential treatment of Overwatch followed by Boxer Gold produced higher yield than the single herbicide treatments.

A field trial was undertaken in 2020 to investigate the effects of sowing time, canola variety, seed rate and herbicides on annual ryegrass management at a high rainfall site in South Australia (Frances). As expected, canola plant density was also significantly influenced by the seed rate (P<0.001). The lower seed rate had 26 plants/m2 as compared 52 plants/m2 in the higher seed rate. Therefore, crop seed rates selected were able to achieve the target crop density. Delayed sowing did not have any effect on in-crop ryegrass density (P=0.355). Application of pre- and post-emergent herbicide treatments resulted in a significant reduction in ARG plant density. However, there were no differences in ARG plant density between the herbicide treatments. These trends were also reflected in ARG spike density. The large amount of spikes produced by ARG in all the treatments indicates high tiller production by the plants that survived herbicide treatments as well as later emergence of ARG at this site. ARG spike production, which is the main determinant of its seed production, was significantly affected by canola variety (P=0.007). Hybrid variety Hyola 650TT was able to reduce ARG spike density by almost 50% compared to open-pollinated Wahoo. As seen with ARG spike density, canola variety had a significant effect on ARG seed set. Hybrid canola Hyola 650TT reduced ARG seed set by 73% as compared to the open-pollinated Wahoo (P=0.017). Herbicide treatments also had a significant effect (P=0.014) on ARG seed set. The treatment where Select + Factor + Atrazine were used post-emergent was the best performer with significantly lower ARG seed set than the other three treatments. Addition of Factor (butroxydim) has been shown to significantly improve control of clethodim resistant ARG populations. Canola variety selection also had a significant effect on grain yield (P<0.001). Hyola 650TT produced significantly higher grain yield than the open-pollinated Wahoo. These results clearly highlight the benefits of good early vigour of the hybrid variety for grain yield and weed suppression in this high rainfall environment.

A field trial was undertaken in 2019 to investigate combinations of faba bean sowing time, seed rate and herbicide treatments to control annual ryegrass. 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.

• Propyzamide provided stable and effective ryegrass control at both sowing times. In contrast, simazine + Trifluralin by itself or followed by clethodim was more effective in TOS 2 than in TOS 1. It is possible superior soil moisture conditions at sowing in TOS 2 may have improved weed control in these treatments.
• Increased crop ground cover from higher faba bean seed rates reduced ryegrass growth and spike density. An increase in faba bean seed rate from 20 to 40 seeds/m2 reduced ryegrass spike density from 35 to 21 spikes/m2 (41%).
• The combination of propyzamide followed by Factor + Clethodim was able to almost eliminate ryegrass spike production (0.1 spikes/m2). Previous studies have also shown improvement in ryegrass control when Factor (butroxydim) is added to clethodim when treating clethodim resistant populations.
• Faba beans sown on 26 May produced significantly greater grain yield than the crop sown on 22 June. This is consistent with general grower experience of superior performance of faba beans when sown early.
• As ryegrass density at the trial site was low (<35 plants/m2), grain yield of faba beans in herbicide treatments ranged from 2.48 to 2.65 t/ha and was unaffected by herbicide treatments (P=0.309). These results suggest faba beans can tolerate low ryegrass densities without suffering any loss in grain yield. However, failure to effectively control low ryegrass densities can lead to large build-up in ryegrass seedbank for subsequent crops.

A field trial was undertaken near Winchelsea, VIC to investigate the effect of faba bean sowing time, seed rate and herbicide treatments on annual ryegrass (ARG) control. ARG plant density was unaffected by the seeding date but was significantly influenced by the herbicide treatments. The results of seed production were somewhat surprising. As expected in such a long growing season, the use of pre-emergent treatment of Simazine + Triflur X IBS was unable to provide adequate weed control and resulted in the highest ARG seed set. The results also show that the post-emergent application of Select and Factor were relatively ineffective when used in TOS 1. However, the post-emergent treatments were highly effective in TOS 2. Previous research has shown reduction in the efficacy of these herbicides under cold and frosty conditions as in this study. Crop seed rate had a significant effect on faba bean grain yield (P<0.001) but time of sowing did not influence grain yield (P=0.61). Grain yield increased significantly as seed rate increased from low (4.65 t/ha), medium (5.96 t/ha) to high seed rate (6.51 t/ha). At this high rainfall site, simply relying on pre-emergence herbicides proved inadequate. Simazine + Triflur X had a significantly lower grain yield than faba beans sprayed with a combination of pre- and post-emergence herbicides. Even though the highest ARG plant density present at the site was 33 plants/m2, it was quite competitive with the crop (P=0.01) and reduced its yield by 0.4 t/ha as compared to the treatments where Select or Select + factor were used as post-emergent treatments.

A field trial was undertaken at Washpool in 2019 to investigate combinations of wheat sowing time, seed rate and herbicide treatments to control annual ryegrass. The average seedbank of annual ryegrass (ARG) at the site was 2249 ± 284 seeds/m2. There was no evidence at this site of any reduction in ryegrass infestation in wheat by delaying sowing by three weeks between TOS 1 (77plants/m2) and TOS (74plants/m2). This result suggests the Washpool ARG population likely has a high level of seed dormancy, reducing the rate of ryegrass germination after the opening rainfall events. Herbicide treatment had a significant influence on ARG plant density (P<0.001). Boxer gold and Sakura + Avadex reduced ARG plant density by 45% and 73% from the untreated control (125 ARG plants/m2). Wheat was much more competitive against ARG when it was sown early. This was made evident by the large increase in ARG seed production when seeding was delayed. When averaged across all other treatments TOS 1 produced 1634 ARG seeds/m2, which was 73% lower than 5974 ARG seeds/m2 produced in TOS 2 (P=0.013). Wheat seed rate had a significant influence on ARG seed production (P=0.005), with the high wheat seed rate supressing ARG seed production by 37% when compared to the lowest wheat seed rate (100 seeds/m2). Wheat grain yield at this site was significantly influenced by the time of sowing (P=0.001), seed rate (P=0.001), herbicide treatments (P=0.001), and the interaction between the time of sowing and herbicides (P=0.011). Wheat was much more tolerant to ryegrass competition when sown early (TOS 1) as shown by the small increase in grain yield in herbicide treated plots. In contrast, there was a significant increase in wheat grain yield in herbicide treatments in TOS 2. The results of this study clearly show that delayed sowing of wheat allows for greater seed set by ryegrass and is also associated with a large yield penalty.

• Herbicide treatments had a significant (P<0.001) effect on ryegrass density. The highest ryegrass plant density was observed in Boxer Gold; other herbicide treatments provided significantly greater weed control than Boxer Gold.
• Boxer Gold treatment was also the worst performer in terms of ryegrass spike density with 223 ryegrass spikes/m2. Overwatch and Sakura + Avadex Xtra provided significantly greater suppression of ryegrass spikes than Boxer Gold. The best result was obtained where Overwatch applied before seeding was followed by Boxer Gold at 1-2 leaf stage of ryegrass.
• Boxer Gold was the lowest yielding treatment, which was consistent with its highest ryegrass spike density. Herbicide treatments that provided greater reduction in ryegrass spike density resulted in higher wheat grain yields.
• Overwatch followed by Boxer Gold was the highest yielding treatment in this trial (5.26 t/ha). The results of this trial highlight the importance of increasing the duration of herbicide activity in high rainfall areas such as Frances.

• The site mean for ARG plant density was 845 plants/m2, which is a reflection of the high seedbank. Delay in sowing from TOS 1 to TOS 2, reduced ARG plant density by 27% in the control (knockdown only). Further delay in sowing (TOS 3), reduced ARG plant density by 39%. Among herbicide treatments, Overwatch + Avadex Xtra provided the greatest reduction ARG plant density in all TOS.
• As wheat seed rate was increased from 100 to 200 seeds/m2, ARG spike density declined by 37%, which is quite similar to the previous results. Further increase in wheat seed rate had a marginal additional benefit for reducing ARG spike density.
• As wheat seed rate increased from 100 to 200 seeds/m2, ARG seed set decreased by 41%. Further increase in wheat seed rate to 300 seeds/m2 only had a small additional effect on ARG seed set.
• When only the knockdown herbicide was used to control ARG (control), wheat grain yield increased with delayed sowing, which is most likely due to improvement in ryegrass control. However when pre-emergent herbicides were used, wheat yield declined with delay in sowing. In these pre-emergent treatments, grain yield declined by >1 t/ha as crop sowing was delayed from 21 May (TOS 1) to 27 June (TOS 3).
• Yield improvements of more than 3 t/ha were achieved by combining early sowing with optimum wheat seed rate and effective pre-emergent herbicides.

A field trial was undertaken in 2020 to investigate combinations of wheat sowing time, seed rate and herbicide treatments to control annual ryegrass. Increase in wheat seed rate from 100 to 200 seeds/m2 caused a significant reduction in ARG spikes and seed set. The level of additional weed suppression from higher wheat seed rate ranged from 30-35%. As expected, both pre-emergent herbicides caused a significant reduction ARG plant density, spikes and seed production. Even though there was a general trend for Sakura to be slightly more effective than Boxer Gold, these differences were non-significant. It is somewhat disconcerting to note that even with the use of the tank mix of Sakura + Avadex Xtra, ARG was able to set more than 34,000 seeds/m2. These results highlight the need for integrating multiple weed control tactics to drive down the populations of this resilient weed. Wheat grain yield at Roseworthy ranged from 1.85 t/ha to 3.48 t/ha and with a site mean across all treatments of 2.773 t/ha. Time of sowing wheat did not have a significant effect on wheat grain yield in 2020 (P=0.168). However, wheat grain yield was significantly influenced by crop seed rate (P=0.023) and herbicide treatments (P=0.001). There was no interaction between these management factors. As seed rate increased from 100 to 200 seeds/m2, wheat grain yield steadily increased by 15%. Herbicide treatments had a highly significant (P<0.001) effect on wheat grain yield in this trial, which was not surprising considering the high ARG seedbank and weed density. Application of Boxer Gold and Sakura + Avadex Xtra increased wheat yield by 41% and 54% compared to the untreated control.

Key messages
• This field trial at Roseworthy was undertaken to investigate factorial combinations of canola seed rate and herbicides on the management of annual ryegrass (ARG).
• Canola seed rate had a significant effect on crop density (P<0.001). Crop density achieved was 30 plants/m2 for the low seed rate and 50 plants/m2 for the high seed rate.
• ARG plant density in various canola cultivars x weed management strategies was <100 plants/m2 (Table 6). Among herbicide tolerant crops, Truflex® (TF) glyphosate tolerant system and LT (LibertyLink® + Triazine tolerance) canola had a significantly lower ARG plant density (P=0.019) than the TT (triazine tolerant) canola. Within a canola cultivar, differences in ARG plant density were only observed in TT canola where application of clethodim alone or clethodim + butroxydim significantly improved ARG control as compared to pre-emergent herbicides alone (HT 1 and 2).
• There were significant differences between canola cultivars in ARG spike density. Application of propyzamide before sowing followed by two applications of glyphosate in TF canola reduced ARG spike density to less than 1 spike/m2. In contrast, spike density of ARG in TT canola was significantly greater (42-191 spikes/m2). As ARG population present in the trial paddock was glyphosate susceptible, use of this herbicide on TF canola proved extremely effective for ARG control.
• When averaged across the four weed management strategies, TF (Nuseed Raptor) canola (4.338 t/ha) produced significantly higher yields than TT (HyTTec® Trophy) (3.669 t/ha) and LT (Invigor® LT4530P) (3.523 t/ha) (P<0.001; LSD = 0.189).
• In this trial, glyphosate application in the TF canola not only provided excellent ARG control, but it also had excellent agronomic features, which resulted in grain yields well above 4 t/ha. Even though the differences between the herbicide treatments in TF canola were small, application of propyzamide pre-sowing gave a significant increase in yield relative to sole reliance on post-emergent glyphosate (HS 2 vs 4). Use of pre-emergent herbicide is likely to have reduced competition from ARG during the early vegetative stages prior to the use of glyphosate. Use of multiple modes of action is also beneficial for delaying the evolution of herbicide resistance in ARG populations.

Wheat plant density was significantly affected by the planting arrangement (P=0.027) and the herbicide treatment (P<0.001). The Ribbon seeder system had the highest wheat density (196 plants/m2) as compared to the knife-point system (180 plants/m2) and the Zero row spacing (177 plants/m2). Wheat plant density in the inter-row space in the Zero row spacing treatment was reduced by Treflan + Avadex and Boxer Gold. Annual ryegrass plant density was only affected by the herbicide treatments (P<0.001). Pre-emergent herbicide activity was much lower than expected (24-29% efficacy) and is likely to be due to extremely dry soil conditions at the site (decile 1 growing season). Similarly, the reduction in ryegrass spike density by the herbicides relative to the untreated control was low and ranged from 6 to 24%. There was no significant reduction in ryegrass seed production by the herbicide treatment, which was surprising because Sakura and Boxer Gold did reduce ryegrass spike density. Ryegrass was able to produce 18-20,000 seeds/m2 in different herbicide treatments, which highlights the poor efficacy of pre-emergent herbicide in dry conditions. Herbicide treatments had a significant effect on wheat grain yield with Sakura producing the highest yield (2.31 t/ha), closely followed by Boxer Gold (2.13 t/ha). Sakura and Boxer Gold treatments increased wheat grain yield by 29% and 19% compared to the untreated control, respectively.  These results show that ryegrass was quite competitive against wheat under the dry conditions experienced in 2018. The treatment of Sakura ($40/ha) increased wheat yield by 0.5 t/ha compared to the untreated control, which would have improved the gross margin by $150/ha.

Wheat plant density was significantly affected by the planting arrangement (P=0.012). The Ribbon seeder system had the highest wheat density (171 plants/m2) as compared to the knife-point system (156 plants/m2) and the Zero row spacing (151 plants/m2). The establishment of wheat plants in the inter-row space in the Zero row spacing treatment was strongly influenced by the pre-emergent herbicide treatment (P=0.002). Trifluralin, Avadex or Boxer Gold were higher risk pre-emergent herbicides for wheat establishment, whereas Sakura appears much safer where wheat seed is placed on the soil surface in the Zero row spacing system. Annual ryegrass (ARG) plant density was not significantly affected by the planting arrangement (P=0.513) or pre-emergent herbicide treatments (P=0.13). ARG spike density was not significantly influenced by wheat planting arrangement (P=0.185). Herbicide treatment did have a significant influence on ARG spike density (P=0.023) and ARG seed production (P=0.003). The best performing herbicide treatment of Sakura + Avadex still produced 16824 ARG seeds/m2. While this is 51% lower than the Treflan + Avadex, it will replenish the soil seedbank to a highly problematic level for the future. Wheat grain yield was significantly affected by the planting arrangement (P=0.034) and the herbicide treatments (P=0.004). Even though the differences in wheat yield were small <10% for planting arrangement and <14% for herbicide treatments, they were statistically significant.

The herbicide treatment had a significant effect on ARG density (P<0.001) in this field trial at Minnipa. Favourable rain events in June were highly suitable for the activity of both pre-emergent herbicides investigated in this trial. Averaged across the row spacing and SBU treatments, Boxer Gold and Sakura + Avadex reduced ARG plant density by 88% and 90%, respectively. The density of ARG spikes was significantly influenced by the herbicide treatment.  Boxer Gold reduced ARG spike density by 74% compared to the untreated control, whereas Sakura + Avadex caused 85% reduction in ARG spike density. The density of ARG spikes in Sakura + Avadex were significantly lower than in the Boxer Gold treatment. ARG seed production was also significantly affected by the herbicide treatment (P<0.001) but not by wheat row spacing (P=0.272) or seed boot design (P=0.994). ARG produced 5740 seeds/m2 in the untreated control, which was reduced by 74% by Boxer Gold and 86% by the mixture of Sakura + Avadex. Presence of ARG at 190 plants/m2 in the untreated control, reduced wheat grain yield by 11% compared to Boxer Gold or 8% compared to Sakura + Avadex. However, it was still profitable to control ARG with effective herbicide treatments. Based on cash grain price of Australian Premium Wheat (APW) of $400/t in 2018, Boxer Gold would be expected to increase the gross margin by $68/ha as compared $12/ha increase for Sakura + Avadex.

Key messages
• Lentil seed rate had a significant effect on crop density (P<0.001), which was within 10% of the target density range of 80 to 160 plants/m2.
• ARG plant density was significantly affected only by the herbicide treatments (P<0.001). Good soil moisture at crop sowing in 2022 were ideal for the activity of pre-emergent herbicide propyzamide, which reduced ARG plant density by 79% compared to the untreated control.
• The trial site has group 1 resistant ARG population, which was reflected in large ARG plant survival when sprayed with the post-emergent clethodim + butroxydim herbicide treatment (79% ARG control). However, the sequential application of pre-emergent propyzamide followed by the post-emergent herbicides substantially increased ARG control to 88%.
• Consistent with the results for ARG plant density, herbicide treatments caused a significant (P<0.001) reduction in its spike density. The combination of pre-emergent herbicides followed by the post-emergent treatments reduced ARG spike density by 86 to 91%. These trends are likely to be also reflected in ARG seed set, which tends to be highly correlated with spike density.
• As lentils are a weak competitor against weeds, herbicide treatments had a highly significant impact on crop yield (P<0.001). Use of pre-emergent propyzamide alone more than doubled lentil grain yield. Pre-emergent application of propyzamide followed by post-emergent clethodim + butroxdim was the best treatment with grain yield of 4.369 t/ha as compared to 1.303 t/ha in the untreated control.

Key messages
• A field trial was undertaken at Gladstone in 2022 to investigate combinations of wheat seed rate and herbicide treatments on annual ryegrass (ARG) control.
• Even though the increase in wheat plant density from 100 to 250 plants/m2 reduced ARG spike density by 19%, this was not statistically significant (P=0.225). However, ARG spike density was significantly affected by different herbicide treatments (P<0.001).
• Surprisingly Sakura® (pyroxasulfone) was relatively ineffective with more than 700 spikes/m2. In contrast, Overwatch® (bixlozone) treatment had significantly less ARG spike density. The most effective herbicide treatment was the combination of Overwatch® immediately before crop sowing (IBS) with early post-emergent (EP) Mateno Complete® (aclonifen, pyroxasulfone, and diflufenican).
• Overwatch® by itself produced wheat yield of 6.2 t/ha, which was almost 1 t/ha higher than Sakura®. The highest crop yield (7.03 t/ha) was achieved in the treatment where Overwatch® was followed by early post-emergent application of Mateno Complete®.

Key messages
• Increase in field pea plant density from 40 to 60 plants/m2 by higher seed rate treatments significantly reduced ARG plant and spike density, and increased field pea grain yield. However, the major driver of ARG density and crop yield in this trial was herbicide treatments (P<0.001).
• Large ARG seedbank present at the trial site resulted in continued weed establishment for at least 2 months after sowing, which was reflected in inadequate ARG control by pre-emergent propyzamide alone.
• This trial site has group 1 resistant ARG population, which was reflected in inadequate weed control by the post-emergent clethodim + butroxydim treatment (64% ARG control). The sequential application of pre-emergent herbicide treatments followed by post-emergent herbicides substantially increased ARG control to 86-93%.
• Field pea grain yield increased from 2.19 t/ha at the lowest crop density to 2.65 t/ha at the highest density, a gain of nearly 0.5 t/ha. This improvement in grain yield is likely to be associated with improved weed suppression at the higher seed rates.
• Effective herbicide treatments more than doubled field pea grain yield by reducing competition from ARG. Pre-emergent application of propyzamide followed by post-emergent clethodim + butroxydim was the best treatment with grain yield of 3.1 t/ha as compared to 1.2 t/ha in the untreated control.

A field trial was undertaken at Watchman in 2020 to investigate combinations of barley sowing time, seed rate and herbicide treatments to control brome grass. The average seedbank of brome grass at the site was 2140 ± 178 seeds/m2. Delaying sowing by three weeks did not impact on barley establishment (P=0.368) and brome grass plant density (P=0.417). However, delayed sowing of barley did have a significant effect on brome panicle density (P=0.019) and it had an interaction with herbicide treatment on brome seed production (P=0.049). This lack of an effect of delayed sowing on brome plant density, compared to other brome sites indicates presence of high seed dormancy in Watchman population. Barley seed rate did not have a significant effect on brome panicle production (P=0.854), or brome seed production (P=0.392). However it did have a small, but significant impact on barley yield with a 6% increase in grain yield when barley seed rate was increased from 100 to 200 seeds/m2 (P=0.049). Increase in barley seed rate also significantly reduced barley grain contamination with brome grass seeds by 38% (P=0.049). Herbicide treatments had a significant effect on brome plant density (P<0.001), brome panicle density (P<0.001), brome seed production (P<0.001), brome grain contamination (P<0.001), and barley grain yield (P=0.023). Where IMI herbicide treatments were applied in this trial, brome grass control was improved greatly, which resulted in an increase in barley grain yield. These IMI herbicides were effective in providing high levels of brome grass control and should be considered a very useful tool in the management of brome grass. While herbicide resistance to these herbicides is common in annual ryegrass, IMI resistance in brome grass is far less common. However, over reliance on IMI herbicides should be avoided in order to preserve their activity for the future.

Canola establishment was significantly influenced by the variety (P=0.012) and seed rate (P<0.001). Greater plant density in the hybrid variety T4510 (36 plants/m2) than the open pollinated Bonito (31 plants/m2) is likely to be associated with the larger seed size and greater early vigour in the hybrid. Plant density achieved was within 10% of the target density. There was a significant interaction between sowing time of canola and herbicide treatments (P=0.004). This interaction was mainly associated with a significantly lower brome grass density in the control (glyphosate). In contrast, brome grass density was very similar between the two sowing dates where pre-emergent and post-emergent herbicides were used. Consistent with the trend of brome grass panicle density, brome grass seed production in this trial was significantly influenced by the herbicide treatment (P<0.001). The results also show that brome grass panicles set more seeds when only the knockdown or Atrazine IBS was used (49-59 seeds/panicle) as compared to post-emergence Haloxyfop treatments (30 seeds/panicle). Canola grain yield was significantly affected by the time of sowing (P=0.034), with the earlier sown crop (1.58 t/ha) producing higher yield than the later sowing (1.35 t/ha). The hybrid variety Invigor T4510 (1.56 t/ha) produced significantly higher grain yield than the open-pollinated Bonito (1.37 t/ha) (P<0.001). Increase in canola plant density from 25 to 50 plants/m2 also caused a significant increase in grain yield (P=0.002), even though the yield improvement was only 100 kg/ha. Even though brome grass density at the site was fairly low (~12 plants/m2), herbicide treatments had a significant positive effect on canola grain yield (P<0.001). Controlling brome increased income by $169/ha or 21% after including the cost of the herbicides and applying the herbicides when averaged across the trial.

A field trial was undertaken at Mallala in 2019 to investigate combinations of wheat sowing time, seed rate and herbicide treatments to control brome grass. The average seedbank of brome grass at this site was 2877 ± 406 seeds/m2. The two week delay in sowing reduced average in-crop brome density from 567 plants/m2 to 352 plants/m2 (38%). Even though the reduction in brome density at Mallala was significant, it was a much lower reduction than that observed in the trial at Riverton (82% reduction). This difference in brome grass density with delayed sowing at these two sites highlights the large differences in seed dormancy between the populations of this weed species. Brome grass panicle density was significantly affected by wheat seed rate (P=0.039), and herbicide treatment (P<0.001) but not by the time of sowing (P=0.152). Increasing seed rate of wheat suppressed brome grass growth and reduced its panicle density. As wheat density increased from 100 seeds/m2 (low) to the highest seed rate (200 seeds/m2 – high) brome panicle density was reduced by 39%. These results support previous findings that higher crop density can be an important part of an integrated weed management program. Wheat grain yield increased consistently with the increase in seed rate or crop density. This trend correlates well with the improved suppression of brome grass panicle density observed in the trial. Not only did higher wheat density achieve superior weed suppression, it also provided a significant increase in grain yield. Herbicide treatments also had a highly significant effect on brome grass panicle density. However, there was no interaction herbicides and TOS or seed rate. This indicates that herbicides performed similarly in both times of sowing and the three seed rates. Sakura + Avadex significantly reduced panicle density as compared to Treflan + Avadex and Intercept (Clearfield technology) was used after pre-emergent Treflan + Avadex, it prevented brome plants from producing panicles (3 panicles/m2). Herbicide treatments had a large and significant effect on grain yield of wheat at Mallala (Figure 5). This is not surprising considering the high weed density present at the site and high competitive ability of brome grass. The treatment of Treflan + Avadex produced only 1.11 t/ha, which was significantly lower than the more expensive pre-emergent herbicide mixture of Sakura + Avadex (1.81 t/ha). However, when Intercept post-emergence herbicide was used, wheat yield increased further to 2.63 t/ha. In this trial, integration of Clearfield technology with pre-emergent herbicides not only prevented brome grass seed set as shown but the panicle density, it also delivered the highest grain yields.

A field trial was undertaken at Riverton in 2019 to investigate combinations of wheat sowing time, seed rate and herbicide treatments to control brome grass. The average seedbank of brome grass at the site was 1863 ± 303 seeds/m2. Brome grass at this site was effectively controlled (>80%) by delaying sowing by 2 weeks, with treatment effects from herbicide and wheat seed rate treatment only being significant in the early sown plots, where brome grass density was high. These results clearly indicate that brome grass population present at this site has very low seed dormancy and germinates readily after the season opening rains and can be effectively controlled with a knockdown herbicide. Wheat grain yield results reflected the level of brome grass control with herbicide and wheat seed rate treatments improving yields significantly as brome suppression improved. These treatments did not have a significant effect on yield when sowing was delayed because brome was effectively controlled by the knockdown herbicides. In the early sown crop when brome grass was controlled effectively with Intercept®, the 2 week delay in sowing caused a 9% reduction in wheat yield.

A field trial was undertaken at Minnipa in 2019 to investigate combinations of barley sowing time, seed rate and herbicide treatments to control annual ryegrass. The average seedbank of annual ryegrass (ARG) at the site was 4168 ± 411 seeds/m2. 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<0.001). There was a large impact of the 3 week delay in seeding barley on ARG plant density. This was particularly evident in the untreated control in which ARG density decreased from 676 plants/m2 in TOS 1 to 379 plants/m2 in TOS 2. This large reduction in ARG density due to delayed sowing is most likely related to rainfall events in early May, which would have caused weed emergence. Pre-emergence herbicides had higher efficacy in TOS 2 where the density of ARG plants had been reduced by the delay in seeding. This trend held through the season in the untreated control in which ARG spike density decreased from 306 spikes/m2 in TOS 1 to 199 spikes/m2 in TOS 2. In the trifluralin treatment, ARG produced 5078 seeds/m2 in TOS 2 as compared to 9192 seeds/m2 in TOS 1, a 45% reduction in ARG seed production. Unlike wheat in 2018, barley grain yield at Minnipa was not significantly influenced by the time of sowing (P=0.644). However, seed rate (P<0.001), herbicide treatment (P<0.001) and had a significant effect on barley grain yield. As stated earlier, there were large benefits of delayed sowing on weed control. In barley a three week delay did not significantly reduce grain yield as it had in the previous year in wheat. Lower yield penalty in barley from delayed sowing may be related to its earlier maturity than wheat.

• Three week delay in seeding barley reduced annual ryegrass (ARG) plant density by 45% in the control (knockdown only) and by 28% for the weaker Trifluralin treatment. However in the most effective herbicide treatments (Boxer Gold and Overwatch), high levels of ARG control was achieved in both TOS 1 and TOS 2.
• The interaction between sowing time and herbicide (P<0.001) was reflected in 45-50% lower ARG spike density in TOS 2 than in TOS 1 for the control and Trifluralin treatments. However, no such effect of delayed sowing was observed for the more effective treatments of Boxer Gold and Overwatch that reduced ARG spike production by 81% and 78%, irrespective of sowing time.
• Barley seed rate did have a significant effect on ARG seed production (P=0.022) with crop sown at 150 and 200 seeds/m2 having 29% and 21% lower ARG seed set than seed rate of 100 seeds/m2. It is a serious cause for concern that ARG was able to set 7705 and 8700 seeds/m2 in the most effective herbicide treatments Boxer Gold and Overwatch. These results highlight the need for growers to integrate tactics such as improved crop competitiveness and harvest weed seed control along with herbicides to achieve a decline in the seedbank of this difficult to manage weed.
• Herbicide treatment had a significant effect on barley grain yield with Trifluralin (1.99 t/ha) increasing grain yield by 16%, Overwatch (2.30 t/ha) 34% and Boxer Gold (2.33 t/ha) by 36% compared to the control (1.72 t/ha). These yield gains approximately equate to a 5:1 return on the cost of Trifluralin, a 4.5:1 return on Overwatch and a 5.8:1 return on Boxer Gold.  

Barley grain yield as significantly influenced by the time of sowing (P=0.025), seed rate (P<0.001) and the herbicide treatment (P<0.001). The delay of 4 weeks between the two sowing dates caused 22% (0.69 t/ha) reduction in grain yield or 25 kg/ha/day. Averaged over the two sowing dates and three seed rates, Boxer Gold treatment (2.996 t/ha) produced significantly greater barley grain yield than Treflan (2.634 t/ha) and the control (2.648 t/ha). Barley sown early (TOS 1) at high seed rate and sprayed with Boxer Gold produced 3.6 t/ha grain yield as compared to later sown crop (TOS 2) at low seed rate but treated with the same herbicide which produced 2.4 t/ha.

A field trial was undertaken at Washpool in 2020 to investigate combinations of barley sowing time, seed rate and herbicide treatments to control annual ryegrass (ARG). The average seedbank of ARG at the site was 1949 ± 496 seeds/m2. Time of sowing significantly influenced ARG plant density, with lower ARG plant density when seeding was delayed (P<0.001). Herbicide treatment had a significant influence on ARG plant density (P<0.001) due to 58% reduction in ARG plant density by the tank-mix of Boxer Gold and Trifluralin compared to the untreated control (155 plants/m2). Herbicide treatments also reduced ARG spike density and seed production. The mixture of Boxer Gold and Trifluralin reduced ARG spike density and seed production compared to the untreated controls by 45% and 42% respectively. ARG seed set was significantly lower in TOS 1 (18,911 seeds/m2) than in TOS 2 (30,990 seeds/m2) (P<0.001). Even though there was a higher ARG plant density in TOS 1 than TOS 2, greater competitive ability of early sown barley was able to reduce ARG spike density and seed production. Barley grain yield at this site was significantly affected by the time of sowing (P=0.014) and herbicide treatments (P=0.009). The control of ARG by the mixture of Boxer Gold and Trifluralin was reflected in barley yield improvement. The results of this study clearly showed that delayed sowing of barley can reduce ARG plant density but reduced competitive ability of the later sown crop often allows greater seed set by ryegrass that is also associated with a yield penalty.

General application of Sakura + Avadex over the whole trial site provided good control of ARG. As a result, follow-up application of Boxer Gold @ 1.5 L/ha or 2 L/ha at GS 11 (1-leaf stage) did not significantly reduce ARG plant density.  Post-emergence application of Boxer Gold at 1.5 or 2 L/ha after pre-emergence Sakura + Avadex extended the period of weed control, which reduced spike density of ARG (P=0.02). At both sowing times, increase in wheat plant density from 100 to 200 plants/m2 reduced ARG spike density by 44%. Delayed sowing at this site reduced the competitive ability of wheat against ARG. Averaged across the seed rates and herbicide treatments, ARG produced 234 spikes/m2 in TOS 2 as compared to 75 spikes/m2 in TOS 1 (68% reduction in TOS 1). Additional post-emergence application of Boxer Gold significantly increased wheat grain yield (P=0.008) compared to the baseline treatment of Sakura + Avadex. Wheat yield increased by 9% or 0.4 t/ha with the additional post-emergence treatment of Boxer Gold as compared to Sakura + Avadex treatment alone. Wheat grain yield was also significantly affected by wheat seed rate (P<0.001). Wheat grain yield increased from 4.6 t/ha at the density of 100 plants/m2 to the maximum of 5.48 t/ha at the seed rate of 200 plants/m2. This yield gain of 0.9 t/ha clearly indicates that early sowing, wheat density of 200 plants/m2 and effective use of herbicides can have a large influence on the profitability of wheat in the HRZ.

Wheat grain yield at Minnipa was significantly influenced by the time of sowing (P=0.002), seed rate (P<0.001), herbicide treatment (P<0.001) and the interaction between the time of sowing and herbicide treatments (P<0.001). Averaged across the seed rates and herbicide treatments, wheat produced grain yield of 1.67 t/ha in TOS 1 as compared to 1.06 t/ha in TOS 2. There were large benefits of delayed sowing on weed control. However, these benefits came at a significant cost in wheat grain yield.

Annual ryegrass (ARG) spike density and seed production were significantly reduced when seeding was delayed by two weeks (P=0.015 and P=0.017). This was not expected as ARG plant density was not significantly different between TOS 1 and TOS 2. Greater seed production by ARG in TOS 1 than in TOS 2 appears to be associated with good rainfall in late spring, which was used effectively by ARG but the crop was approaching physiological maturity and could not make use of increased plant available water. Crop type had a significant influence on ARG seed production with 23 to 53% lower ARG seed production in other cereals than Scepter wheat. Both ARG spike density and ARG seed production were significantly influenced by the herbicide treatment (P=0.017 and P=0.052). The new herbicide Overwatch® provided 30% greater ARG control than Boxer Gold®. Crop type also had a significant influence on grain yield (P<0.001), with barley generally yielding higher than wheat. Herbicide treatment had a significant influence on grain yield (P<0.001), where a 30% greater ARG control by Overwatch® than Boxer Gold® resulted in a 14% improvement in grain yield.

The trial site at Mallala was infested with a large seedbank of group A resistant brome grass, which made weed control in canola very difficult. Furthermore, the trial site experienced drought like conditions for most of the growing season which reduced the efficacy of atrazine. Even though the two-week delay in sowing reduced brome grass density from 927 plants/m2 in TOS 1 to 704 plants/m2 in TOS 2 (25%), this difference was not statistically significant.  However, the herbicide treatments (P=0.005) and the interaction between sowing date and herbicides (P=0.006) had a significant effect on brome grass plant density. Herbicide performance at the site was negatively affected by dry conditions and group A resistance in brome grass. As a result, even the best treatment combinations had more than 300 panicles/m2, which could lead to a large seed set in brome grass. When averaged across the sowing time, seed rate and herbicides, HyTTec Trophy produced 38% higher grain yield than Bonito. This difference in variety performance is consistent with superior crop establishment in HyTTec Trophy than Bonito. As a result of herbicide resistance in brome grass, yield increase in the Verdict treatment compared to the control (atrazine POST) was non-significant. However, use of clethodim increased yield by 61% compared to the control, which was statistically significant.

Barley plant density was significantly influenced by the time of sowing (P=0.025) and crop seed rate (P=0.002).  Averaged across the seed rates and herbicide treatments, the first time of sowing (TOS 1) had barley density of 125 plants/m2 compared to 82 plants/m2 in TOS 2, which was related to dry soil conditions after sowing in TOS 2. Brome grass plant density was significantly affected by the time of sowing (P=0.018) and the herbicide treatments (P<0.001).  The 4-week delay in sowing between TOS 1 and TOS 2, allowed greater emergence of brome grass seedlings before the sowing of the TOS 2.  Consequently, barley sown at TOS 2 had 48% lower brome grass infestation (107.9 plants/m2) than in TOS 1 (207 plants/m2). As expected, herbicide treatments had a significant (P<0.001) effect on brome grass density. When averaged across the sowing time and seed rates, the treatment of Treflan + Avadex was only moderately effective and reduced brome grass density by 36% (173 plants/m2) relative to the untreated control (271 plants/m2). In contrast, the same pre-emergent treatment (Treflan + Avadex) followed by Intervix reduced brome grass density by 90% (28 plants/m2). When averaged across seed rates and herbicide treatments, the time of sowing barley had a significant effect on its grain yield (P=0.011). TOS 1 produced 940 kg/ha greater barley grain yield than TOS 2. The post-emergence application of Intervix to the crop treated with Treflan + Avadex further increased barley grain yield by 872 kg/ha. These results are consistent with the trends in brome grass density and panicle production. The untreated control plots produced 40% lower grain yield than the Intervix treatment, which completely controlled brome grass. These results highlight the strong competitive ability of brome grass in cereals.

The average seedbank of ARG at the site was 3932 ± 270 seeds/m2. 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<0.001). The delay in seeding from TOS 1 to TOS 2 (16 weeks) caused a large reduction in ARG plant density. This was particularly evident in the untreated control in which ARG density decreased from 825 plants/m2 in TOS 1 to 31 plants/m2 in TOS 2 (96% reduction). This large reduction in ARG density due to delayed sowing is most likely related to an effective knockdown herbicide treatment after most ARG had emerged before TOS 2. Herbicide treatments reduced ARG plant density significantly in TOS 1, however herbicide effect on ARG plant density in TOS 2 was non-significant, possibly due to a much lower ARG density. While the delay in sowing significantly reduced ARG plant density (P<0.001), it did not significantly reduce ARG seed spikes (P=0.495). This result indicates that despite low ARG plant numbers in TOS 2, faba beans failed to compete effectively with ARG and suppress its growth. As a result, even at a relatively low density ARG was able to produce a large amount of seed for future infestations. Faba bean grain yield at Frances was significantly influenced by the time of sowing (P=0.033), seed rate (P<0.003), and herbicide treatment (P<0.001). Averaged across the seed rates and herbicide treatments, faba beans produced grain yield of 1.34 t/ha in TOS 1 as compared to 1.81 t/ha in TOS 2. Superior faba bean grain yield in TOS 2 In 2018 at Frances is most likely due to the reduction in ARG plant density.

A field trial was undertaken at Frances in 2019 to investigate combinations of barley sowing time, seed rate and herbicide treatments to control annual ryegrass. The average seedbank of annual ryegrass (ARG) at the site was quite low (472 ± 143 seeds/m2), which was reflected in low plant density at the site. ARG plant density was significantly influenced by the time of sowing (P=0.037), and herbicide treatment (P=0.009). There was a 37% reduction in ARG plant density between TOS 1 (20 plants/m2) and TOS 2 (13 plants/m2). Herbicide treatment had a significant effect on ARG plant density, with Boxer Gold showing lower efficacy on ARG than Treflan and Boxer Gold + Treflan. Unlike ARG plant density, ARG spike density was not influenced by time of sowing (P=0.171). ARG spike density was significantly influenced by barley seed rate (P=0.016), herbicide treatment (P=0.01) and the interaction between TOS and herbicide treatment (P=0.019). ARG spike density was 34% and 40% lower in medium and high seed rates respectively when compared to the low seed rate. These results suggest an improvement in ARG suppression from increasing barley competiveness with increased seed rate. Barley grain yield at the site averaged 6.6 t/ha. Herbicide treatment had a small (4-6%), but significant effect (P=0.009) on grain yield with Boxer Gold < Treflan ≤ Boxer Gold + Treflan for barley yield.

Key messages
• A field trial was undertaken at Roseworthy in 2022 to investigate the effect of combinations of wheat seed rate and herbicide treatments on crop yield and annual ryegrass (ARG) control.
• The increase in wheat plant density in the range of 100 to 300 plants/m2 improved suppression of ARG seed production (17-30%) and increased wheat grain yield (15-21%). However, herbicide treatments were the major driver of wheat grain yields and ARG suppression (P<0.001).
• The trial site had a large ARG seedbank that resulted in heavy and prolonged weed establishment. This was evident from inadequate ARG control achieved with pre-emergent herbicides alone. The trial site also had a detectable level of trifluralin resistance, which would have reduced efficacy of Trifluralin + Avadex Xtra® treatment.
• The sequential application of pre-emergent herbicides followed by an early post-emergent herbicide reduced ryegrass seed set by 94% compared to the untreated control and increased wheat yield by 4.57 t/ha.
• There was an exponential relationship between nitrogen recovery by wheat and ARG seed set, which accounted for >89% of the variation. Wheat plant density and herbicides treatments had a significant influence on nitrogen recovery in grain where only 300 wheat plants/m2 recovered nitrogen equivalent to fertiliser N applied. Only herbicide treatments achieving >60% ARG suppression achieved nitrogen recovery greater or equivalent to applied fertiliser N.

Pre-emergent herbicide treatments had a significant effect on annual ryegrass (ARG) plant density (P<0.001), ARG spike density (P<0.001) and its seed production (P<0.001). Wheat seed rate on the other hand, did not have any effect on ARG spike density or ARG seed set. In this trial, the lowest target wheat density was 150 plants/m2, which appears to be adequate for providing competition with ARG. Even with the use of the best pre-emergent herbicide treatments, ARG was able to produce more than 28,000 seeds/m2. These results indicate that even with the best pre-emergent herbicides currently available, ARG seedbanks are likely to build-up after the wheat phase in problem paddocks. Therefore, integration of pre-emergent herbicides with tactics such as harvest weed seed control is extremely important. ARG was highly competitive with wheat in this trial, which was reflected in large yield increases in the effective treatments. For example, wheat yield increased by 70% (1.4 t/ha) in the Overwatch® treatment compared to the untreated control. In contrast Boxer Gold®, which had higher ARG spike density also provided a smaller increase in wheat grain yield.

Herbicide strategy 1 (HS1), which was based on atrazine pre-sowing followed by clethodim (Select) post-emergence reduced ryegrass plant density relative to the untreated control by 57%. However, use of propyzamide pre-sowing, followed by atrazine and Select + Factor (HS 2) increased ryegrass control to 77%. Canola variety had a significant effect on ryegrass spike density (P=0.002). When averaged across the sowing dates and herbicide strategies, ryegrass growing in HyTTec Trophy produced 52 spikes/m2 as compared to 78 spikes/m2 in Bonito (33% reduction). HyTTec Trophy is a new hybrid triazine tolerant variety from Nuseed, which is known for high early vigour. Herbicide strategies also had a significant effect on ryegrass spike density (P<0.001). Ryegrass grown without any selective herbicide treatment (control – HS3) produced 128 spikes/m2 as compared to 40 spikes/m2 in HS1 and 29 spikes/m2 in HS2. This works out to 69% reduction in HS1 relative to the control and 78% reduction in HS2. Herbicide strategies had the largest effect on canola yield (P<0.001). HS1 and 2 produced canola yield of around 0.8 t/ha, which was almost 50% greater than the yield obtained in the control.

The herbicide treatment had a significant effect on annual ryegrass (ARG) plant density (P<0.001) in this field trial at Minnipa. Favourable rain events in May were highly suitable for the activity of both pre-emergent herbicides investigated in this trial. Averaged across the row spacing and seed boot treatments, Trifluralin and Boxer Gold reduced ARG plant density by 20% and 90%, respectively. The density of ARG spikes was significantly influenced by the row spacing (P<0.001), seed boot treatment (P=0.027), and the herbicide treatment (P<0.001). The 25cm row spacing had 20% lower ARG spike density than the 37.5cm row spacing treatment. The splitter seed boot treatment had 12% lower ARG spike density than the narrow seed boot treatment. Trifluralin only reduced ARG spike density by 20% compared to the untreated control, whereas Boxer Gold caused a 73% reduction in ARG spike density. ARG seed production was also significantly affected by the row spacing (P=0.003), seed boot (P=0.01), and the herbicide treatment (P<0.001). The normal (25 cm) row spacing set 38% less seed than the wide row spacing. The splitter seed boot treatment also had 32% lower ARG seed set compared to the narrow seed boot. ARG produced 4792 seeds/m2 in the untreated control, which was reduced by 11% by Trifluralin and 69% by Boxer Gold. Presence of ARG at 262 plants/m2 in the untreated control, reduced barley grain yield by 8% compared to Trifluralin or 16% compared to Boxer Gold. However, it was still profitable to control ARG with effective herbicide treatments. Based on cash grain price of Feed Barley of $250/t in 2019, Trifluralin would be expected to increase the gross margin by $32/ha as compared $71/ha increase for Boxer Gold.

• Barley crop establishment was significantly reduced in the wider row spacing treatments. This is most likely due to increased crop intra-row competition rather than fertiliser toxicity from reduced seed bed utilisation (SBU) as fertiliser was banded for crop safety and crop establishment was similar for the two seed boot treatments.
• Herbicide treatments achieved varying levels of annual ryegrass (ARG) control with Trifluralin reducing ARG plant density by 30%, Overwatch 67% and Boxer Gold 88% compared to untreated control (1092 ARG plants/m2).
• Improved crop competition in narrower row spacing was reflected in 28% lower ARG seed set in the 25cm row spacing than the wider 37.5cm row spacing. Even though Boxer Gold reduced ARG seed set by 86% compared to the control, ARG was still able to produce 4787 seeds/m2. Such a high level of ARG seed production is likely to have a serious impact on crops grown next year.

The herbicide treatment had a significant effect on annual ryegrass (ARG) plant density (P<0.001) in this field trial at Minnipa. Favourable soil moisture in early May was suitable for the activity of both pre-emergent herbicide treatments investigated in this trial. Averaged across the row spacing and seed boot treatments, Boxer Gold + Trifluralin and Sakura + Avadex reduced ARG plant density by 71% and 72%, respectively. The density of ARG spikes was significantly influenced by the row spacing (P<0.001), seed boot treatment (P=0.002), and the herbicide treatment (P<0.001). The 25cm row spacing had 43% lower ARG spike density than the 37.5cm row spacing treatment. The splitter seed boot treatment had 35% lower ARG spike density than the narrow seed boot treatment. Boxer Gold + Trifluralin reduced ARG spike density by 68% compared to the untreated control, whereas Sakura + Avadex caused a 70% reduction in ARG spike density. ARG seed production was also significantly affected by the row spacing (P<0.001), seed boot (P=0.003), and the herbicide treatment (P<0.001). The normal (25 cm) row spacing set 53% less seed than the wide row spacing. The splitter seed boot treatment also had 39% lower ARG seed set compared to the narrow seed boot. There was a 73% reduction in ARG seed production in the normal row spacing and splitter boot treatment compared to wide row spacing with single seed boot treatment. ARG produced 15483 seeds/m2 in the untreated control, which was reduced by 62% by Boxer Gold + Trifluralin and 67% by Sakura + Avadex. This level of ARG seed production would be more than adequate to allow problematic weed establishment in crops grown next year. Therefore, growers need to consider integration of harvest weed seed control or other management tactics for ARG management. Presence of ARG at 76 plants/m2 in the untreated control, reduced wheat grain yield by 29% compared to Boxer Gold + Trifluralin or 30% compared to Sakura + Avadex.

• While large differences in seedbed utilisation (SBU) were achieved with row spacing and seed boot treatments (7.9 – 22.1% SBU), it had a smaller impact on ARG suppression in this trial compared to previous trials.
• Averaged across the row spacing and seed boot treatments, Boxer Gold (850 ARG plants/m2), Overwatch (118 ARG plants/m2) and Sakura (422 ARG plants/m2) reduced ARG plant density by 49%, 93% and 75%, respectively compared to the untreated control (1680 ARG plants/m2).
• The 25cm row spacing had 17% lower ARG spike density than the 37.5cm row spacing treatment (P=0.007).
• Boxer Gold reduced ARG spike density by 58% compared to the untreated control, whereas Overwatch and Sakura caused an 84% and 82% reduction in ARG spike density, respectively.
• Grain yield in the 25 cm row spacing treatment (5.979 t/ha), was 14% greater than the yield in 37.5 cm row spacing treatment (5.243 t/ha).