Spot spraying pays dividends
Independent research conducted by Syngenta in Germany and Ireland is shedding new light on the efficacy and economic argument for spot spraying from digital maps and on-board optical imaging.
These findings follow field trials by James Thomas, head of precision application EU+ in Ireland and by Thies Schmoldt, Syngenta precision application specialist in sugar beet in Germany. In 2022 they began exploring the viability of spot spraying, as well as the efficacy and economics of the operations.
This research does confirm the systems produce a huge decrease in chemical use. It also, however, reveals a significant reduction of the phytotoxic impact of some selective herbicides on the treated crop, with considerable increases in yield and quality that produces a far greater financial benefit than chemical savings alone.
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Spot spraying sugar beet
For the sugar beet trials in Germany Thies Schmoldt investigated spot spraying in sugar beet. For this he employed a ‘prescription map’ from images scanned by drone – rather than spot spraying in real time with boom-mounted cameras.
These trials showed the spot treatment produced a considerable €300/ha increase in value due to better sugar yield, compared with a ‘blanket treatment’. At the same time, they reduced chemical costs by €38-€45/ha.
Sugar beet is an obvious spot spraying target because conventional treatments can be very costly – up €300-€500/ha from the normal, up to six applications/season. There is also already concern about crop development being affected by phytotoxicity from some herbicides.
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Economically feasible
While mechanical weeding is increasing in popularity, at about €55/ha, it is quite costly. This makes it economically feasible to fit spot spray technology and it’s estimated that 30% of growers in Germany already have sprayers sufficient section widths and control to achieve considerable savings.
“In 2023 we recorded savings of 70% with the second post-em application, while with the same sprayer in a field on the same farm it resulted in no savings at all in the second pre-em timing in 2024,” explains Thies.
“The later application timings often contain not only the most costly herbicide, but they also use a quite potent mix,” explains Thies. “It is quite clear to see stunting caused by phytotoxicity in the crop treated conventionally (blanket coverage) compared with the one that was spot sprayed.”
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Standard sprayers
The trials were carried out in two locations, using three different, but unmodified sprayers:
- A Horsch Leeb 5LT with a 36m wide boom with 25cm and 50cm nozzle spacings and PWM.
- An Amazone UX 8201 with a 36m wide boom, with 50cm nozzle spacing, without PWM or single nozzle control (1.5m minimum section width).
- A Fendt Rogator, with 27m wide boom, 50cm nozzle spacing and individual nozzle control.
SAM Dimension, a start-up from Stuttgart, provided the drone weed mapping images. Its patented camera is specifically designed to create high resolution imagery. “While it may be necessary to have a 2mm resolution in some crops, 4mm is good enough to distinguish weeds from the crop and this can be achieved at workrates of 80ha/hr,” adds Thies.
Prescription maps are easily transferred to existing sprayer terminals, explains Thies, in this case an Amazone Amtron4 and John Deere GS5. “Transfer is not an issue with the latest versions of modern terminals, but they do need the processor power to handle all the individual spots,” he adds.
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Grassland gains
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.
- 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 to expanded, larger scale trials in 2023 in Tipperary in Ireland, where there is a large area of intensively farmed grassland and farmers’ have 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.
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Thorough test
The trial covered 850ha in 320 fields involving 65 growers, using 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. The larger financial gain, however, came from reduced phytotoxicity, which can stunt the grass growth by eight to ten days, resulting in an up to 30% yield increase.
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.
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.
