Optical spot spraying currently sits right at the top of the application tech tree, but it’s been slow to take off. Targeting the technique to where it has the most impact, however, does show big benefits.
Independent research conducted in Germany and Ireland by Syngenta is shedding new light on the efficacy and economic argument for spot spraying from digital maps and on-board optical imaging.
While the systems do produce a huge decrease in chemical use, the reduction of the phytotoxic impact on the treated crop is proving to produce a considerable yield increase, which results in the biggest economic benefit.
These findings follow field trials by James Thomas, head of precision application EU+ and his team at Syngenta. In 2022 they began exploring the viability of spot spraying, as well as the efficacy and economics of the operations.
Syngenta trials in Germany, tested spot spraying in sugar beet from a ‘prescription map’ from images scanned by drone – rather than spot spraying in real time. This technique generated huge gains with the chemical savings of up to €45/ha (£38/ha), but these were dwarfed by up to a €300/ha (£250/ha) benefit from a 10% increase in sugar yield, due to reduced phytotoxicity compared with blanket spraying.
In Ireland the Syngenta study employed an on-boom crop scanner and real time spot spraying to control weeds in grassland. It produced considerable chemical savings, but the higher economic benefit came from up to 30% increased grass yields – compared with a blanket selective herbicide application.
Optical spot spraying
Optical spot spraying (OSS) uses on-board cameras to identify and spray weeds in real time, with precisely targeted treatments.
These systems deliver spray on demand in real time and are most effective in broad acre crops with low weed populations. They employ different detection algorithms to spot ‘green on brown’ or ‘green on green’.
There are a number of retrofit and stand-alone systems available in the UK including WeedIt, CarbonBee, Bilberry and Ecorobotix.
Systems compared
Green on brown systems were first developed for working in dry, arid conditions, for example in Australia and the USA. Here the relatively low weed populations are easier to spot where they stand out against the brown soil.
“Weeds can be treated fairly easily using non-selective herbicide and in these vast fields spot spraying leads to huge savings of up to 80% compared with a blanket, overall treatment,” explains James.
Green on green systems, for spotting weeds in growing crops, are far more complex, calling for far higher levels of computer vision technology. “The vision algorithms are also considerably more complex because, for a start, the crop and weeds are the same colour – and often look similar.
“It is easier, however, to identify the target if it is different shape or size. Spotting and spraying docks in grassland, for example, is now relatively straightforward.
“It’s also effective in crops grown in uniform row and plant spacings – where there is often also more bare soil. These tend to be higher value crops, in which it is much easier to justify the investment – particularly when you take into account higher yields from reduced phytotoxicity, compared with blanket selective herbicide treatments,” he explains.
Spot spraying grassland
To assess how the systems work and their viability, James and the team ran a ‘proof of concept’ trial in 2022, with a CarbonBee optical spot sprayer on a 12m wide Kuhn sprayer.
They treated 25ha and compared this set-up with other existing alternatives to spot and kill thistles, docks and nettles, with encouraging results.
- 70% product saving
- 85% efficacy compared with 75% from knapsack and quad bike
- Five times faster than knapsack and quad bike
- Clear interest from growers.
These positive results led James and the team to expand the trials to a larger scale in 2023. They chose to do this in Tipperary in Ireland because of the large area of intensively farmed grassland and farmers’ progressive attitudes to technology.
For this work they used a 15m Hardi Master sprayer, which was retrofitted with boom recirculation, a Capstan Pulse Width Modulation (PWM) system, individual nozzle control and CarbonBee optical spot spray sensors and control.
All the real time data was captured and analysed on MyJohnDeere to validate the business case.
Thorough test
The trial covered 850ha in 320 fields involving 65 growers. They used five different products to treat a range of weeds, including docks, thistles, ragwort, nettles, buttercup and rushes.
The standard ‘blanket’ treatment cost €114/ha, while the OSS cost just €25.45/ha – a saving of €88.55.
They also assessed the efficacy, checking the OSS system’s effectiveness at spotting and killing weeds. Results show it controlled 70% of the docks and between 40% to 45% of the thistles, nettles and ragwort. On the downside, 60% of the clover was also killed.
“This shows while the algorithm was capable of spotting the docks, it not so effective at spotting other weeds and, obviously, unable to identify clover,” remarks James.
Overall, however, the results are encouraging:
- Reduced phytotoxicity, which can stunt the grass growth by eight to ten days, resulting in up to 30% yield increase
- Ability to better manage grazing rotation, allowing OSS fields to grazed more quickly (some farms had 40% treated with a standard blanket coverage)
- Fertiliser cost saving from no need to apply nitrogen to offset the stunting caused by blanket spraying.
Trials will continue in the future with a different optical spot spraying system with co-development of algorithms. These will be designed to better target thistles, nettles and ragwort and, crucially, avoid treating clover.
Big benefits in beet
In Germany, Thies Schmoldt, Syngenta precision application specialist, focused on spot spraying sugar beet from prescription maps generated from high resolution crop scans gathered from a drone.
The crop is an obvious spot spraying target because treatments can be very costly – up to €300-€500/ha from the normal, four to five applications a season, with the concern that SU herbicides can cause phytotoxicity.
Mechanical weeding is increasing in popularity, but it is costly at about €55/ha, which makes it economically feasible to fit spot spray technology. It is estimated in Germany 70% of growers already have sprayers suitable for retrofitting the kit.
Trials were carried in two locations, one with a Horsch and the other with an Amazone sprayer, with a minimum viable section size of 1.5m as well as single nozzle control.
Results show enormous savings in chemical costs of up to 80% on two occasions, 70% for the first application and 35% in the second at the other location.
“The third timing application is not only the most costly herbicide, but the mix also has quite potent phototoxicity,” explains Thies. “It is quite clear to see how stunted the crop treated conventionally (blanket coverage) compared with the one that was spot sprayed.”
This was also reflected in the costings with a €300/ha increase in value due to better sugar yield, as well as chemical savings of €38-€45/ha.
Need NRoSO or BASIS points?
Get ahead. Get points.
Enrol today to earn all 10 NRoSO points. Why wait?