Weighing up the automated spot-spraying tech options

In the southern and western regions, adoption has recently started to ramp up, largely in response to increasing glyphosate resistance and incursions of troublesome summer weed species such as fleabane and feathertop Rhodes grass.

In response to increasing complexity, automated spot-spraying (using either sensors or cameras) gives growers multiple levers to pull using different chemistry, timings and rates. Automated spot-spraying has an important role in managing herbicide resistance risk and is a key tactic in the WeedSmart Big 6 ‘optimise spray efficacy’ strategy.

Fallow spot-spraying using ‘green-on-brown’ weed detection has been available in Australia since the Brownhill family at Spring Hill, in northern NSW, imported Trimble’s first WeedSeeker in 2002, and Rometron’s WEED-IT soon followed. Both WEED-IT and WeedSeeker use technology first developed as a research tool in the mid-1980s by NSW DPI researcher Warwick Felton, who demonstrated the concept could save growers up to 80 per cent of their fallow herbicide costs. The infrared sensors on these sprayers detect the chlorophyll in weeds growing against a background of stubble or bare earth.

With the advent of artificial intelligence, big data and more accessible camera technology, researchers saw the opportunity to investigate the possibility of identifying different plant types by their leaf shape, flower or plant architecture. Small, high-resolution RGB cameras take and rapidly process images using computer algorithms to determine if certain plants are present. These systems are as accurate as the infra-red sensors at distinguishing between plants and soil or stubble in fallow (green-on-brown) settings.

In 2016, three French engineers saw weeds as a commercialisation opportunity for this new technology, and Bilberry began developing ‘green-on-green’ spot-spraying in Australian cropping environments. Bilberry commercialised their fallow spot-spraying system in 2018 and joined the Trimble stable in 2022. For in-season use, the Bilberry system currently detects broadleaf weeds in cereal crops (wheat, barley and oats), and there are also advanced algorithms for detecting blue lupins in narrow-leaf lupin crops and grasses in canola crops. The Bilberry camera system is the only* option for green-on-green spot-spraying in Australia and is available through partner sprayer manufacturers such as Goldacres, Millers and AgriFac. (* BeeLeap has recently released a commercial green-on-green product available in Australia)

John Deere has also developed camera spot-spraying capability, which is incorporated in its See and Spray range of self-propelled sprayers. The See and Spray Select is the only model available in Australia, offering fallow weed detection only. However, other models in the range provide in-crop spraying in the USA and may be imported into Australia in the near future.

One major benefit of automated spot-spraying is the ability to apply higher herbicide rates to very small areas on a paddock (less than 20 per cent paddock area). Nufarm has recently registered several products, and many others are listed on an APVMA permit, for automated (optical) spot-spraying in fallow, vastly increasing the tactic’s value in stopping weed escapes before they set seed.

For in-season spot-spraying, specific registrations and permits will likely follow as opportunities for different use patterns emerge. For now, green-on-green spot-spraying uses existing registered products, rates and timings. The immediate advantage is the capability to target weeds before canopy closure without spraying the whole crop, potentially improving overall yield. A follow-up tactic such as spot-spraying rather than broadcast crop-topping to stop seed set of late germinated weeds and or harvest weed seed control bolsters the value of early spot-spraying.

Automated spot-spraying platforms with dual-tank and dual-line delivery systems to apply different chemical solutions have a distinct advantage. For example, this capability allows a blanket residual herbicide application plus a spot-spray knockdown in one pass in fallow; or a herbicide spot-spray and a blanket fungicide application in-crop.

Another future benefit of artificial learning lies in the potential for variable-rate application of insecticides, fungicides and trace elements using camera systems and relevant algorithms.

For all systems, height control is critical for accurate detection and spraying. Keeping the sensors or cameras stable is central to achieving a high degree of accuracy and no misses. Most systems also offer optional or in-built night spraying, various spray delivery mechanisms and weed mapping options.

Some considerations when making your choice:

• What is your main weed concern? For many growers, automated spot-spraying in fallow situations is the highest priority. For fallow use alone, the sensor systems provide the highest accuracy and no annual use fees. Growers who see multiple uses for green-on-green weed detection might consider having the capability for fallow and in-season applications well worthwhile.
• Spot-spraying has maximum impact if deployed multiple times during the fallow or cropping season. Detecting and spraying very small weeds maximises herbicide efficacy and reduces herbicide resistance risk. However, this extra use may impact the depreciation of specialised machinery such as self-propelled sprayers. Some growers are retaining older SP sprayers or purchasing trailing booms for their spot-spraying work. Spot-spraying is also well-suited to robotic platforms.
• Upfront and annual costs. The capital outlay is similar for all the current sensor and camera systems. The WeedSeeker, WeedIT and See and Spray Select machines only require the initial machinery purchase. Machines with Bilberry systems on-board have a purchase price for the machine and an annual usage subscription capped at $11,000 paid for both green-on-brown and green-on-green weed detection. If John Deere brings their See and Spray Premium and Ultimate models with green-on-brown and green-on-green weed detection to the Australian market, a usage subscription fee will be attached.
• Retro-fit and quick-release kits. Some systems can be fitted to a variety of sprayer brands, while others are fully integrated with particular machines. Removing and storing the sensors or cameras between seasons may extend the life of the hardware.
• Spray delivery systems. Different levels of nozzle control are available. Some systems trigger a section of nozzles, while others have single-nozzle control. The ones with single-nozzle control offer a side-safety setting, where the nozzles on either side will also spray to ensure adequate coverage of the detected weed.
• There are only a few dual-tank spot-spraying machines currently on the market in Australia. Several manufacturers are keen to add to their offering, as this is a deal-breaker for many growers wanting to use two chemical solutions in one pass for a broadcast and spot-spray application. Some machines can deliver two rates (broadcast and spot-spray) of the same solution to target different-sized weeds.

The reduction in chemical volume applied is well-established with spot-spraying technology, and many new and innovative use patterns are being developed that will provide growers with more ways to increase the diversity of their weed management program.

The WeedSmart Big 6 strategy embraces herbicide and non-herbicide weed control tactics to keep weed numbers low in cropping systems. 

More resources

Optical sprayer return on investment (ROI)

Spot spray herbicide registrations and permits

Practical considerations in low-weed environments