Weeds and herbicide resistance genes do not obey borders. While fencelines, roads and channels cut across different production systems weeds and herbicide resistance often move easily across enterprises. Weeds that are problematic in irrigation systems, for example, may spread into dryland cropping systems, and vice versa.
To understand the novel dynamics, GRDC has joined with the Cotton Research and Development Corporation, Agrifutures Australia and the Australian Government to invest in research into weed management across a landscape. Called area-wide management (AWM), the approach involves looking for additional weed management benefits that arise when considering weeds beyond the fencelines of an individual farm.
The predominant weeds under investigation are fleabane, feathertop Rhodes grass and ryegrass – weeds which were of most concern to surveyed stakeholders and which have highly mobile seeds or pollen. Some other weeds are also being studied, including silverleaf nightshade.
This initiative is headed by project leader Dr Rick Llewellyn at CSIRO, with the work undertaken as a partnership with researchers at the University of Adelaide, the University of Queensland, the University of Wollongong and with farming groups such as Mallee Sustainable Farming, Millmerran Landcare Group, Irrigation Research and Extension Committee Inc, together with input from Wine Australia, the Toowoomba Regional Council and a range of additional local industry organisations.
Dr Llewellyn says the project has initiated work in three regions selected for their highly diverse land use – the Darling Downs, Sunraysia and the Riverina.
“Our focus is on mobile weeds that spread across boundaries and impact different sectors – grains, rice, cotton, viticulture and horticulture – as well as move from public land like roadsides,” he says. “Rather than focusing just on weed impacts on individual paddocks, we look at the broader implication of weed movement across boundaries and districts.”
The highly collaborative team are finding there is a lot to be gained from minimising spread, especially where the weed or resistance is not yet widespread in a district or where a land manager has a zero-tolerance approach.
“The aim is to identify where more-coordinated strategies will ultimately benefit all land users – including minimising spread to neighbours,” Dr Llewellyn says.
In Sunraysia, the focus is on how weed and glyphosate resistance move in a landscape that includes dryland grain paddocks adjacent to irrigated orchards and vines. The idea is to look for practices that do not just reduce the risk of weeds to each enterprise but the movement of mobile weed seeds between enterprises.
On the Darling Downs trial work involves the Toowoomba City Council and is looking at roadside weed management to suppress weed movement into adjacent paddocks.
In the Riverina, the focus is on channel bank management to suppress the risk of weed seeds moving with channel water across highly diverse production systems – rice, grain, cotton, vineyards and other horticulture. In this area, studies have also aimed to stop weed seed set in vineyards through more effective herbicide options.
The project is focused on four key areas:
- the use of genetic analysis to map how weeds are related to each other, thereby revealing how they moved across a landscape and the impact different land uses had on that movement. This is a particular focus of research at the University of Queensland, headed by Dr James Hereward;
- mapping the pattern of glyphosate resistance of the weeds most capable of moving across landscapes (including roadsides), with the work headed by Professor Chris Preston at the University of Adelaide;
- understanding the social and economic perspectives of different land users, with regards to the barriers they face to taking more area-wide approaches. The social aspects of more collaborative approaches are a particular focus at the University of Wollongong led by Dr Sonia Graham; and
- trialling local management practices to reduce weed seed-set and the potential for spread, including through the release of biocontrol agents.
With the project not due to end until 2023, trials and testing are still underway; however, some key lessons have already emerged.
Landscape-scale mapping
Every weed sample collected for analysis throughout the life of the project came with GPS coordinates. The geolocation data allow both the weed’s genetic ancestry and its herbicide resistance status to be overlayed onto geographical maps. Over time, this kind of data reveals the way both weeds and resistance genes are moving across a landscape.
A rich tapestry of new insights is emerging with the potential to refine weed control strategies. Examples abound.
When it comes to fleabane, for instance, Dr Hereward says this weed has a reputation for long-distance dispersal by wind.
However, the population genetics analysis performed at the University of Queensland identified something important. “We found that local dispersal may be a more-important driver for fleabane genetics than long-distance dispersal,” Dr Hereward says. “The relatively short life of the seedbank also leads to rapid population turnover.”
The analysis also found little evidence for genetic structure in feathertop Rhodes grass populations within the Darling Downs region, and none for annual ryegrass within the Riverina. This indicates the potential for high levels of movement of these two species across the regional landscape.
Similarly, important nuances are turning up in the analysis of glyphosate resistance levels in fleabane. Professor Preston says substantial frequencies of glyphosate resistance were identified in all weeds and in all districts and reached as high as 81 per cent of annual ryegrass samples in the Murrumbidgee Irrigation Area in 2021.
In the Riverina, glyphosate resistance was found across the range of land uses. This includes 60 per cent of samples from agricultural land (crop, orchard, vineyard), and 54 per cent of samples from the edge of roads, tracks and channels being resistant.
“While glyphosate resistance levels may seem high and may surprise some people, the distribution of resistance highlights that there are incentives to remaining vigilant and acting to reduce the risk of spread,” Dr Rick Llewellyn says.
The distribution reveals a scattered pattern that is inconsistent with the notion of a moving front of resistance, for example, north to south. Scientists take that to mean that localised efforts to prevent the spread of resistance to neighbours and roadsides are working.
“Getting an understanding of weed mobility is a key step in formulating viable AWM strategies,” Dr Llewellyn says. “The sampling we undertook in this project is on a scale big enough to help inform how best to deploy AWM in different situations to have the biggest impact. In lots of cases there are opportunities to take action to reduce the risk of spread to a neighbour – including reducing the risk of spread from public land, like roadsides, onto paddocks.”
Social analysis
AWM boils down to a having a shared goal of controlling weeds and mitigating herbicide resistance. Having a shared understanding of the impacts of weeds and weed dispersal and building collective motivation to minimise weed-seed on a landscape scale will have a greater impact on weeds than isolated efforts .
As Sunraysia grain grower Clay Gowers puts it: “It boils down to a friendly partnership across the fence.”
Helping to understand the barriers growers face in adopting AWM are social scientists, such as Dr Sonia Graham from the University of Wollongong. Her studies involved interviews and follow-up surveys of about 200 growers in the Sunraysia district.
Dr Graham reports that there is a broad consensus among growers regarding the benefits of working together to manage weeds. One of the main barriers (at 61 per cent of Sunraysia respondents) relates to the extra time required to share information, especially time spent in meetings.
In Sunraysia, the studies found that some 32 per cent of respondents are already taking some form of coordinated action to control weeds, primarily by talking to their neighbours and working together to prevent weed mobility from public land into adjoining enterprises.
Participants in weed AWM tend to categorise as growers who:
- are generally more concerned about herbicide-resistant weeds spreading from their land to neighbouring land;
- are more aware that land managers in their area are collaborating on weed management;
- discuss weed control with their neighbours more frequently;
- receive external support for weed management more frequently;
- are more likely to share information on weed management with other landowners; and
- are more likely to attend meetings on local weed management.
To help more growers overcome barriers to adoption, the survey data is now being analysed in ways that will help make AWM a better fit for growers across sectors. This includes finding efficiencies in how growers interact and who they interact with in order to reduce the amount of time AWM requires, especially time spent in meetings.
Another key aim of the project is to acquire a better understanding of the range of weed management activities that are possible given different scales of adoption among growers.
Activities have included one of the rarer kinds of AWM activities – the release of a biocontrol agent (a rust fungus) against fleabane that was led by AgriFutures Australia (Rural Industries Research and Development Corporation), and funded by the Australian Government Department of Agriculture, Fisheries, and Forestry as part of its Rural Research and Development for Profit program, with co-investment from CSIRO, GRDC and NSW Biocontrol Taskforce. Dr Llewellyn says the regions are particularly excited to be assisting with the release and monitoring.
Through its regional partners, such as Mallee Sustainable Farming, the AWM project has also initiated extension activities that have brought together growers and experts from different sectors to the same event. Examples include WeedSmart’s ‘Being WeedSmart in Horticulture’, a large event held at an almond orchard during September.
“With AWM that’s the key – getting that cross-sector collaborations and the shared knowledge needed to make the most of opportunities for action that benefits individual growers as well as neighbouring land,” Dr Llewellyn says.
This project is supported through funding from the Australian Government Department of Agriculture, Fisheries and Forestry as part of its Rural R&D for Profit program and the Grains Research and Development Corporation and the Cotton Research and Development Corporation.
More information: Rick Llewellyn, rick.llewellyn@csiro.au