Integrated weed management maintains very low weed levels for more than a decade

Page last updated: Tuesday, 4 December 2018 - 12:18pm

Growers have eroded their ryegrass seedbanks by 99.3% from an average of 183 ryegrass/m2 in 2001 to 1.29 ryegrass/m2 in 2018 across the 27 focus paddocks. These growers had already eroded their ryegrass seedbanks by 89% in the first five years of this study. Since then, ryegrass numbers have been maintained at low levels over the remaining 13 years of monitoring.

Most growers are confident that their weed control strategies are working, but they remain worried about the development of resistance. Wild radish and brome grass are becoming more diffucult to manage.

Background

The focus paddocks are an opportunity to monitor weed management data from a range of paddocks that clearly demonstrate the benefits of integrated weed management (IWM). This was a joint DPIRD-GRDC project that began in 2001 when four small grower groups in the Geraldton Port Zone agreed to participate in IWM extension and research.

Ryegrass populations have been monitored at a farm-scale in each of the 27 paddocks for the past 18 years, making the data globally unique. The work, initiated by Peter Newman, has been presented at international conferences around the world and is viewed as one of the greatest examples of how IWM works in real life.

A weed count at the designated site in each focus paddock was conducted in September and October 2018. Counts are the average number of ryegrass plants/m2 counted in spring. These counts represent surviving ryegrass in crop/pasture in that month rather than a measure of the total weed seedbank. The 27 paddocks were split into two groups according to the growers’ use of harvest weed seed control (HWSC); those that are using HWSC (+HWSC) and those that are not using HWSC (-HWSC). To be considered yes for using HWSC, growers must have used HWSC at least four times or used in the past three years in a row.

Results

The 2018 survey counts were added to the ongoing focus paddock weed density graphs produced since 2001 (Figure 1). In 2018, the +HWSC group averaged 0.725 ryegrass plants/m2, with individual paddock averages ranging from 0-5 ryegrass plants/m2. The -HWSC group averaged 1.85 ryegrass plants/m2, with individual paddock averages ranging from 0-10 ryegrass plants/m2 (Figure 2).

While the +HWSC group had lower ryegrass numbers than the -HWSC, it should be noted that weed numbers were exceptionally low across all focus paddocks in 2017 and 2018, therefore dampening the clear trend seen in all of the previous years. Both groups were very successful at eroding the ryegrass seedbank while maintaining their cropping intensity in 2017 and 2018; however, the heavy reliance on herbicides within herbicides-only group is likely to result in higher levels of resistance in these paddocks.

Ongoing focus paddock weed density graphs. Surviving ryegrass in crop or pasture as counted by quadrat in specified location each Spring.
Figure 1 Average surviving ryegrass in crop or pasture as counted by quadrat in specified location each spring for all focus paddocks

Graph focuses on the reduction of ryegrass numbers from 2005. In 2018, the Plus HWSC group averaged 0.725 ryegrass plants/m2 and the Minus HWSC group averaged 1.85 ryegrass plants/m2
Figure 2 Surviving ryegrass plants in spring for growers using HWSC (+HWSC) compared to growers using no or minimal HWSC their cropping programs (-HWSC)

Conclusion

The majority of growers participating in the focus paddocks have been successful at dramatically reducing their weed seedbanks and are continuing to maintain very low levels.

Over the past 18 years of monitoring, the focus paddocks demonstrate that it is possible to continue to farm effectively when faced with a huge herbicide resistance challenge. There is an increasing number of growers adopting, or looking to adopt, harvest weed seed control (HWSC), especially with the evolution of successful, low-cost options such as chaff lining.

Most growers are successfully managing annual ryegrass seedbanks however, these growers comment that they are more concerned about managing brome grass and wild radish. According to many of the growers, these weeds may be harder to manage than ryegrass but all of the practices that are currently being used to manage ryegrass will be applicable to brome grass and wild radish.

This data is essential for monitoring management practices, particularly when faced with ‘weedy’ years like 2018. The results are reflective of the management practices, as it highlights that farmers serious about reducing weed numbers and minimising the risk of herbicide resistance are utilising multiple IWM tools. This study also gives confidence to the notion that, if having enough non-herbicide weed control in a continuous cropping system, growers can achieve long-term success and sustainability.

The continuation of this study is vital for focusing on what IWM strategies are winning the battle against crop weeds. Therefore, in future seasons, paddocks will continue to be surveyed and any new HWSC methods will be monitored as an extension of this study.

References

Focus Paddocks: Case studies of Integrated Weed Management. Peter Newman & Glenn Adam

Focus Paddocks: Case studies of Integrated Weed Management 2nd Edition 2009. Peter Newman

Focus Paddocks: Case studies of Integrated Weed Management 3rd Edition 2013. Peter Newman

Acknowledgments

The department thanks all of the growers involved in the focus paddocks study who were willing to have their paddocks continually monitored although the initial project finished in 2012.

Thank you to Peter Newman for his assistance in providing detailed insight into the study and IWM in general, and to Bonnie Jupp for continuing the study.

Grains Research and Development Corporation (GRDC) for their support of this work being continued within the Regional Research Agronomy project (DAW00256).

GRDC project number: DAW00256 (Building crop protection and crop production agronomy research and development capacity in regional Western Australia).

Contact information

Megan Abrahams

Regions