Green on brown sprayer delivers cost savings
Light-activated sensor-controlled sprayer reduced the overall chemical use by 23% to 55% and resulted in cost savings of $2.36/ac to $12.48/ac ($5.83 to $30.83/ha) across herbicide treatments for kochia and prickly lettuce control.
In recent years, light-activated sensor-controlled (LASC) sprayers have become more popular with custom operators and broadacre farmers in Australia, United States and Canada. These sprayers use a combination of red and near-infrared light with sensors that detect reflected light from green weeds which then activates a solenoid switch connected to a corresponding nozzle. This results in the spray nozzle activating only when a green weed is detected on fallow or crop stubble.
A research project was conducted to evaluate an LASC sprayer for the effectiveness and herbicide cost savings for weed control in postharvest wheat stubble compared to a conventional broadcast sprayer, and to determine the efficacy of LASC spray system for weed control in fallow when operated at two different speeds.
Five individual LASC units were mounted on a metal frame 12 inches (30 cm) apart resulting in a total spray width of 60 inches (150 cm). Each unit contained an AIXR11002 nozzle tip. The frame was mounted on the back of an UTV.
Two experiments were conducted in 2013 and 2014 at the Montana State University Southern Agricultural Research Centre near Huntley, MT. Experiment 1 was conducted in a field with postharvest wheat stubble, and Experiment 2 was conducted in a summerfallow field. The sites were in a no-till dryland wheat-fallow rotation, and had uniform kochia and prickly lettuce populations.
In Experiment 1 on wheat stubble, 11 different herbicides were applied in 16.7 gal/ac (187 L/ha) at 40 psi (276 kPa) at a speed of 3 mph (5 km/h). Weed control was compared between the LASC sprayer and a broadcast sprayer using the same AIXR11002 nozzles. These herbicides included three rates of glyphosate alone, glyphosate + dicamba + 2,4-D, dicamba + 2,4-D, bromoxynil + pyrasulfotole, carfentrazone+ dicamba, paraquat, paraquat + linuron, saflufenacil + 2,4-D, and diflufenzopyr + dicamba + 2,4-D.
The plots were treated about three weeks after winter wheat harvest on August 5, 2013 and August 8, 2014. Kochia and prickly lettuce plants were three to seven inches (8 to 18 cm) tall with a density of 0.6 to 0.8 plants/ft2 (6 to 8 plants/m2). Percentage weed control was measured for each herbicide program and the two different types of sprayers at 14 and 28 days after treatment and total weed biomass reduction at 28 days after treatment.
Weed control similar between LASC and broadcast sprayers
In Experiment 1, the best kochia control was observed with glyphosate at double the field-use rate (2520 g ae/ha), paraquat alone or in tank-mixture with linuron, and saflufenacil + 2,4-D. These herbicides provided 93% to 100% control and were similar for LASC and broadcast sprays. Kochia control with LASC sprayer was significantly lower with bromoxynil + pyrasulfotole and carfentrazone + dicamba compared to broadcast sprayer.
Control of prickly lettuce was generally lower than kochia, and each spray system provided similar control levels for the herbicide programs. Bromoxynil + pyrasulfotole, paraquat alone or in tank-mixture with linuron and saflufenacil + 2,4-D treatments provided 95% to 100% control of prickly lettuce with no significant differences between sprayer systems. Glyphosate at double the field-use rate provided 91 to 93% control while the field-use rate provided 73 to 82% control.
An economic analysis was conducted to compare herbicide costs between the LASC sprayer and broadcast sprayer. The spray solution of each herbicide treatment was measured before and after spraying to calculate the cost of the herbicide plus adjuvant savings from the LASC sprayer.
The overall reduction in herbicide use ranged from 23% to 55% across the herbicide programs, likely due to variation in weed size and densities in the plots.
Chemical savings with the LASC sprayer ranged from $2.36/ac to $12.48/ac ($5.83 to $30.83/ha) compared to the broadcast sprayer. The most expensive herbicide program was the carfentrazone + dicamba tank-mix at $35.66/ac ($88.10/ha), so not surprisingly it had the greatest savings at $12.48/ac despite only reducing herbicide application by 35%. Generally, a higher herbicide cost meant higher cost savings with the LASC sprayer.
Comparison of herbicide plus adjuvants cost and savings for the light-activated sensor-controlled (LASC) versus broadcast sprayer in field experiments conducted in 2013 and 2014 at the Montana State University Southern Agricultural Research Center near Huntley, MT.
Source: Sharma et al. 2023
Speed affected herbicide performance
In Experiment 2, five herbicide programs were tested in chemfallow with the LASC sprayer operating at 5 mph (8 km/h) with AIXR11002 nozzles and 10 mph (16 km/h) with AIXR 11004 nozzles to deliver 187 L/ha at 276 kPa. These included glyphosate, dicamba + 2,4-D, paraquat + linuron, saflufenacil + 2,4-D, and diflufenzopyr + dicamba + 2,4-D. Control of kochia and prickly lettuce was measured 14 and 28 days after treatment.
Experiment 2 treatments were applied on June 5, 2013 and June 18, 2024 when kochia and prickly lettuce was 2.4 to 5 inches (6 to 12 cm) tall with a density of 0.8 to 1.2 plants/ft2 (8 – 12 plants/m2).
Of the five herbicides tested, higher application speed at 16 km/h significantly reduced weed control in four of them. Kochia and prickly lettuce control were reduced by up to 20% when the LASC sprayer was operated at 16 km/h compared to 8 km/h. The herbicide tank-mix of diflufenzopyr + dicamba + 2,4-D produced similar weed control levels at both speeds, however control only ranged from 51 to 60% in prickly lettuce and 63 to 67% for kochia. Kochia and prickly lettuce control with glyphosate, dicamba + 2,4-D, paraquat + linuron, and saflufenacil + 2,4-D in chemfallow was reduced at the higher speed.
Effect of various postemergence (POST) herbicides for kochia and prickly lettuce control in fallow at 28 days after treatment (DAT) using the light-activated sensor-controlled (LASC) sprayer operated at a speed of 8 or 16 km h−1 in field experiments conducted in 2013 and 2014 at the Montana State University Southern Agricultural Research Center (MSU-SARC) near Huntley, MT.
Source: Sharma et al. 2024
At the time, the researchers suggest that the results indicate that a producer may probably spend a little more time (on an area basis) when using this LASC sprayer compared to a conventional broadcast sprayer for achieving effective weed control, but can realize herbicide cost savings, especially with more expensive herbicide programs. A caveat, though, is that the technology has advanced since the research was conducted, and that the weed control efficacy when spraying at higher speeds may have improved.
Sharma, P., Kumar, V., & Jha, P. (2023). Efficacy and economics of light-activated sensor-controlled sprayer for site-specific weed control. Agronomy Journal, 1–10. https://doi.org/10.1002/agj2.21420
