Mallee Sustainable Farming has joined a national project into weed and herbicide resistance – particularly along fence lines, roads and channels.
Project leader Rick Llewellyn says herbicide resistant genes do not follow the rules – or borders – and cut across different production systems, often moving easily across enterprises.
He says weeds which are problematic in irrigation systems, for example, may spread into dryland cropping systems, and vice versa.
Sunraysia is one of three target areas in the project – the others are in the Riverina in NSW and Darling Downs in Queensland.
Dr Llewellyn says in Sunraysia, the focus is on how weed and glyphosate resistance moves in a landscape which includes dryland grain paddocks adjacent to irrigated orchards and vines.
He says 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.
“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.”
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.
Dr Llewellyn says the project initiated the work in three regions after they were selected for their highly diverse land use.
“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 is 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.
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 aim is to identify where more-coordinated strategies will ultimately benefit all land users – including minimising spread to neighbours,” Dr Llewellyn says.
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.
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.
Mapping the pattern of glyphosate resistance of the weeds most capable of moving across landscapes (including roadsides).
Understanding the social and economic perspectives of different land users, with regards to the barriers they face to taking more area-wide approaches.
Trialling local management practices to reduce weed seed-set and the potential for spread, including through the release of biocontrol agents.
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.
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 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.”
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.
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).
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.
