Key Points
- Drone technology is commercially available to provide growers with another option for selective post-emergence herbicide applications.
- Iowa State University completed a field demonstration of weed mapping and an executable prescription on a soybean field.
- Product savings were near 50% and resulted in an economic savings of $13.42/acre from reduced chemical use while showing no significant difference in grain yield compared with control, broadcast treatment.
- Drone-based weed mapping provides a targeted spraying option that allows for the optimization of tank mix and volume, without limitations on speed or interference from dust, and without the up-front costs associated with real-time boom-mounted systems.
Post-Emergence Spray Technology
In recent years, the ag industry has heavily focused on bringing new precision spraying technology to market that allows growers to spray only where weeds exist, reducing application and chemical costs, and mitigating environmental impacts on soil, water and herbicide resistance. Standard management today generally involves broadcast application of herbicide both pre- and post-emergence. Leveraging precision spray technology can provide chemical savings for post-emergence applications where the reduction in cost and chemical usage will depend on the initial weed pressure, but it is not uncommon to see reductions of 50% or higher. John Deere recently reported an average herbicide savings of 59% for See & Spray™ users in 2024 (https://www.deere.com/en/news/all-news/see-spray-herbicide-savings/) while Iowa State University captured savings ranging from 44 – 91% across 5 soybean fields using similar spray technology (Precision Spraying Technology | Integrated Crop Management). Using drone technology to map a field for weeds prior to an application event, Sentera reported data captured over 13,000 acres in 2024 to have 94% weed detection accuracy and delivered meaningful costs savings for post-emergence non-residual herbicides (LinkedIn - Sentera 2024 Early Access Program Results).
Within the precision spraying space, ground-based and aerial application options exist. A recent Iowa State University article outlines ground-based technology where camera systems capable of detecting weeds in real-time are attached to the spray boom (Precision Spraying Technology | Integrated Crop Management). Other options take a multistep approach, using drones to map the field and predetermine where to focus weed control efforts. Prescriptions can be generated from the drone imagery and then imported into either a spray drone, or a sprayer with nozzle control capabilities for targeted spraying. Spray drones perform zone spraying, rather than spot spraying, with minimum zone sizes of about 0.1 acre, and have been used to spray patches of invasive weeds in conservation areas. Ground sprayers with nozzle control can spray areas as small as 0.001 acre already, and active technology advancements are expected to further reduce the minimum spray area per weed. There are several drone and satellite imagery analysis providers offering weed insights including Intelinair (https://www.intelinair.com), Taranis (https://www.taranis.com), Pix4D (https://www.pix4d.com/), and Sentera (https://sentera.com/). Some offerings use low resolution drone or satellite imagery to generate weed pressure maps based on large weeds, which can be used to identify major issues, direct scouting, or hand-draw zones for late-season rescue application of weed escape patches. Others offer tools for the user to generate grids, mark cells that contain weeds, and export a grid prescription. Some of the grid tools will even auto-classify remaining cells after a few minutes of manual marking. Grid tools are primarily used for green-on-brown but have been used for green-on-green in cases of large weeds above the canopy. The mosaics used with grid tools usually have insufficient resolution for detecting the smallest weeds. Others list species present based on high resolution imagery, which can be used for determining tank mixes. Sentera uses high resolution drone imagery to detect weeds 1/4" tall and larger and automatically generates a targeted spray prescription for use in a ground sprayer. To our knowledge, Sentera is the only company currently offering fully automated targeted spray prescription generation suitable for typical post-emergence spray timing in soybeans.
Product Savings
Iowa State University recently completed a field demonstration merging drone technology with a self-propelled sprayer platform. The drone technology explored was Sentera’s Aerial WeedScout (AWS) offering that included a high-precision drone flight used to generate a customized herbicide prescription within 24 hours of drone deployment. This prescription was loaded into a John Deere ExactApply™ machine but can also be uploaded to other sprayers with nozzle control and used to reduce herbicide while maintaining coverage and weed control. Having the executable prescription ahead of application allows for several advantages to real-time boom-mounted sensing systems. Operators can optimize tank mixes and volumes for the weed pressure discovered. The sprayer can be driven at full speed and dust doesn’t impact the pre-planned prescription. Finally, there are fewer up-front costs associated with this method. The reduction in herbicide will be directly related to the detected weed pressure and reductions are not guaranteed.
Figure 1. Ground level view of AWS treatment area at time of spraying.
In this demonstration, Sentera AWS was used to apply 70 gallons of tank mix over 8.7 acres of soybeans post-emergence. A broadcast application of 15 gal/ac over the same area would have resulted in 130.5 gallons of tank mix applied, resulting in a near 50% product savings and $13.42/acre in chemical costs. Weed control success was measured by repeated weed counts across subsections of the field. The initial weed count yielded 118 weeds in the area of interest with a second counting 17 days after executing the AWS prescription, showing herbicide injury on 117 (>99%) weeds. Of the 118 weeds, 111 (94%) were dead. At harvest, the AWS treatment area had a final yield within 1.5 bu/ac of the broadcast control, with no significant difference between treatments.
Figure 2. Aerial WeedScout prescription map provided by Sentera for spraying application.
In summary, effective weed management using Sentera Aerial WeedScout was demonstrated at scale with product savings of ~50% and cost savings of $13.42/acre were achieved. These values were influenced by the initial weed pressure in the field, and one can expect greater savings with lower weed pressure, and smaller savings with higher weed pressure. Harvest data showed yield was not impacted by comparing AWS to broadcast treatment areas. This technology offers another option to the grower’s toolbox for those interested in prescription spraying technologies.