Australian broadacre agriculture is on the cusp of realising a great trifecta – low weed numbers, less herbicide and more crop yield – all riding on technology that can detect and spot-spray weeds within crops.
Nufarm’s green-on-green program director David Keetch says this technology is reaching maturity in Australia, with adoption being driven by demand for the new use patterns that it could enable.
“We started down this road over 20 years ago when growers were able to slash herbicide costs in fallow fields using green-on-brown sensors to target weeds while leaving the rest of the paddock untreated,” he says.
“As adoption grew, regulators and crop protection companies moved to provide the permits and label registrations to support new use patterns in fallow.
“This enabled growers to target hard-to-kill weeds using products and rates that are not economic or safe to use as a broadcast application.”
There is strong demand for in-crop spot-spraying technology in Australia, with manufacturers recognising the Australian horticultural and broadacre cropping sectors as market leaders for adoption.
There are now more than seven manufacturers in the global green-on-green spot-spraying market, exploring a range of weed-detection and herbicide-application methods.
David is leading two GRDC investment projects that aim to validate and expedite green-on-green technology to suit the Australian market and develop a regulation framework for site-specific chemical application to support unique green-on-green use patterns for Australian cropping systems.
Weed detection and spot-spraying technologies fit within the ‘spray efficacy – make every drop count’ pillar of the WeedSmart Big 6 integrated weed management program to minimise the risk of herbicide resistance.
Griffith is hosting WeedSmart Week August 18-19, showcasing how growers can integrate weed detection technologies into their weed management program using numerous Big 6 tactics.
Capturing the benefits in Australian farming systems
In the northern hemisphere, green-on-green technology has achieved excellent results in row crops like corn and soybeans. David says their wide row systems make it easier to identify weeds in the inter-row and to distinguish between the crop and weeds protruding from within the crop row.
“In Australia, narrow rows and high plant density, particularly in cereals and canola, represent real challenges for automated in-crop weed detection,” he says.
“The first green-on-green targets in our systems have been weeds that have very distinct features from the crop they are growing in, such as wild radish and other broadleaf weeds in cereals, and grasses in canola.”
Growers can use green-on-green technology to detect these weeds and apply herbicides at broadcast rates on current registered labels.
Similarly, growers can use weed detection maps to apply pre-emergent herbicides only in areas where weeds were present the previous year.
These use patterns provide cost savings through reduced herbicide volume, but since some of these herbicides are generally relatively cheap, the savings alone may not justify the cost of the green-on-green technology.
To gain productivity benefits like those achieved through green-on-brown technology, David says growers will need access to new use patterns, such as managing herbicide-resistant broadleaf weeds in lentil crops, that will require new registrations.
Other potential use patterns include the introduction of new herbicides, application of herbicides late in the season (without exceeding MRL) or at higher rates to target herbicide-resistant weeds.
These potential use patterns should not overshadow the need to ‘make every drop count’ through effective spray application, targeting small weeds and harnessing the power of crop competition to keep weed numbers low.
The WeedSmart Boomspray Investment Calculator enables growers to use their own farm figures to determine whether investment in different boomspray technology options is profitable for their business.
The calculator is freely available on the WeedSmart website.
Regulation to support widespread adoption of green-on-green technology
Green-on-green technology is an exciting and fast-moving field as manufacturers and industry develop and trial various means to solve a range of pain points in complex scenarios.
Most companies are working with cameras (plus other sensors) either on booms for on-the-go weed detection and spraying, or on drones and satellites to create prescription maps for boomsprays with section control.
Label registrations will need to encompass all these technologies.
Crop protection companies commercialise a relatively small number of the molecules they develop and test.
There are three major barriers to commercialisation.
The first is cost.
A herbicide might be found to be effective, but it is never registered because the production cost is too high for it to be economically applied as a broadcast-spray.
Second, a herbicide may be taken up in the grain or stubble, leaving an unacceptable residue level if it were sprayed over the whole crop.
Thirdly, a herbicide may be too hot for the crop if it were applied over the whole field.
Site-specific application opens up additional opportunities for new herbicides to be commercialised and for existing herbicides to have expanded registration, where their use is shown to be cost-effective, low-residue risk, and cause only localised crop damage when only a small percentage of the field is sprayed.
To ensure crop safety and avoid exceeding the maximum residue level (MRL), regulations and protocols will need to be in place to support the new use patterns that green-on-green technology enables.
This is more complex than the regulation required for green-on-brown spot-spraying, where growers are able to use registered products at the spot-spraying rate, provided the weed density across the paddock is estimated to be below a certain percentage.
When spot-spraying in-crop, both the overall density and the pattern of distribution of the target weed will affect crop safety and chemical residue levels.
Herbicide-resistant weeds are particularly likely to occur along paddock borders and in patches rather than scattered throughout the paddock, increasing the risk of excessive crop damage and elevated residues in grain and grazing stubble within these ‘hot spots’.
Nufarm is collaborating with GRDC and the APVMA to develop new protocols for good laboratory practice and good agricultural practice that are recognised by the Australian regulatory system.
These protocols will enable the registration of new herbicide uses that are not suitable for traditional broadcast application.
These protocols will be available for all registrants wishing to bring new products or use patterns to the Australian market.
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