Is a Drone for You?

Enthusiasm for drone use in agriculture is growing and changing fast. Global industry analysts predict today’s $6 billion agricultural drone market will grow to $18 billion by 2030.

Unmanned aerial vehicles (UAVs) or drone spraying in the United States is ramping up quickly too. According to the American Spray Drone Coalition, acres sprayed by drones increased from 4 million to 10.3 million from 2023 to 2024. Purdue University researchers report an estimated 3,000 to 3,500 registered spray drones in the United States.

Sprayer drone benefits and economics can seem like a no-brainer. Compared with a ground spray rig, drones offer lower costs, lower environmental footprint, easier targeted spraying, no physical crop or soil compaction damage, low water use, lower maintenance and more. However, the mindset change, regulatory requirements, spray coverage differences, insurance and liability costs, and the learning curve can be daunting.

Innovative farmers love to push technology forward, often before researchers prove the application equipment. Drones have already proven their value through improved farming efficiency by gathering crop and field imagery data. Researchers, applicators and farmers are now seeing great potential with larger drones that add spraying efficiency. For example, initial corn/soybean drone spraying of fungicides has seen success since low-volume aerial application by planes and helicopters is already common. 

“Spraying fungicides on corn or soybeans is an easier entry point for getting into drone spraying, compared with controlling 2- to 4-inch weeds,” says Kevin Bradley, weed scientist with the University of Missouri. “Collaborative research strip trial work with my colleague and MU plant pathologist Mandy Bish shows that drones can achieve equal or better disease control and yield to spray planes.”

Early adopter farmers look to expand drone work by aiming at weed control, flying their drone themselves or hiring a service. Currently, Bradley sees more start-up custom application businesses using drones compared with farmer adoption, but farmer interest is growing fast.

Aerial Herbicide Application Rules

Bradley encourages farmers who are shifting to weeds as a drone spray target to understand aerial application labels and review current research because drone-specific labels from crop protection companies aren’t available yet. He posted a corn, soybean and pasture herbicide list of aerial application details, spray volume, restrictions and other parameters in a June 2024 blog post. Always check current labels before applying a herbicide with a drone.

Numerous companies offer larger-size sprayer drones, such as the popular models DJI Agriculture DJI Agras T30, T40 and T50; XAG P100 Pro; and Hylio AG-272. When considering a sprayer drone investment, pay attention to differences in platforms and models such as rotor number and size, tank capacity, weight and wingspan, application speed and height, battery usage, nozzle types, and software/control capabilities. A good book to reference is The Evolution of Spray Drones – Their Capabilities and Challenges for Pesticide Applicators, written by specialists from Purdue University, Auburn University and The Ohio State University.

Watch Swath Width

Bradley’s drone weed control research has focused on spray coverage and water rates to control Missouri’s No. 1 weed problem: waterhemp.

When comparing application between a DJI Agras T40 (3 and 6 gallons per acre) and ground-based sprayers (15 and 20 gallons per acre), there was no difference in weed control despite better droplet size and coverage by ground sprayers.

“We didn’t achieve the desired industry-standard larger droplets with the T40’s rotary atomizer nozzle ‘extra course’ setting,” Bradley says. “Surprisingly, we achieved similar weed control to the ground rigs only in the center of the swath. However, coverage and weed control on the swath edges drops off due to rotor wash and drift of the smaller droplets.”

Setting the correct swath width on a drone is critical to achieving weed control across the full swath width. Bradley says their research with the rotary atomizer nozzle and the spinning disc has shown improved spray coverage on back-and-forth passes when narrowing the swath width from the recommended 30 feet.

Tommy Butts, a weed scientist at Purdue University, says drone swath widths are highly variable and drastically different than ground rig applications. 

The university’s pattern test research used a 20-foot swath width, but the effective control width achieved was closer to 14 feet, even down to 7 feet, depending on nozzle selection and droplet size. Swath reduction diminished due to rotor wash (airflow) pushing droplets to the center, reducing coverage on the swath edges.

Butts conducted a drone-applied spring burndown test with paraquat on winter annuals. The researchers challenged the drone application by using a low label rate on knee-high ryegrass compared with a ground spray rig.

Results showed no “statistically significant” difference in control between the drone at a 5-gallon-per-acre rate (trying various nozzles) versus a ground sprayer at 10 gallons per acre. Plot evaluation after four weeks showed that even the lowest drone application rate of 2 gallons per acre had “statistically equal” control to the 5- and 10-gallon-per-acre spray volumes — showing some real positives as discussed in a webinar presentation. 

However, because researchers use the center of small plots to rate weed control, drone control ratings may be biased due to higher doses in the middle of the swath. Until further research is conducted, university researchers apply caution when making blanket weed control assessments based on the results of early drone spraying research.

Adjuvant and Drift Research Needed

Initial spray deposition research with adjuvants shows variability in coverage and effective spray widths when using drones. Drift retardant agents provided the best results in reducing off-target drift, yet they also significantly reduced the effective swath width. In one Purdue trial, some adjuvants increased weed control compared with the herbicide glufosinate used alone. 

Wind direction certainly has an impact along with speed. As proven with manned spray applicator aircraft, drone spraying into the wind keeps droplets headed to the middle of the pattern, which will likely narrow the effective swath, Butts says. If flying in a crosswind, the finer droplets flow farther downwind, which causes an irregular effective spray width and can impact overlapping coverage passes.

Butts highly recommends conducting pattern tests in advance to find a flight setup (height, speed, overlap, nozzle and adjuvant) that works and stick to it for each type of application (fungicide, herbicide, etc.).

Rigid Regulations

Finally, knowing the regulations are critical to understand whether you plan to spray yourself or hire a service. First, you must register the drone with the FAA, and then take and pass the Part 107 exam for remote pilot certification. The FAADroneZone is a good place to understand the basics. 

Like all ag spray pilots, you must obtain Part 137 certification to dispense agricultural products. It’s also critical to check with your state to obtain necessary pesticide applicator licenses, depending on whether you apply for hire or not. You’ll also need liability insurance to cover aerial applications.

What’s Ahead?

Drone spraying is a new technology that won’t replace spray planes or ground sprayers in the foreseeable future. They will likely become a valuable tool that will overcome early challenges to provide specific successful applications.

The next phase of sprayer drone technology seems headed for hybrid technology, combining gas and electric power to reduce battery and recharging demands. Drone swarms, first introduced by Hylio in 2024 when using three drones, offer the potential to make large acreage applications more efficient as the technology improves.

For a deeper dive:

• Webinar (May 2025): The Ins and Outs of Drone Herbicide Applications (Tommy Butts, Purdue University). https://www.youtube.com/watch?v=Kux4kc7s_NQ 
• University of Missouri Weed Science: Field Evaluation of the DJI Agras T40 UAV for the Application of Herbicides on Soybeans. https://weedscience.missouri.edu/slideshows/uavs_2024.pdf 
• Purdue University. Spray Coverage and Deposits from a Remotely Piloted Aerial Application System Using Various Nozzle Types (Tommy Butts research). https://www.researchgate.net/publication/385656935_Spray_coverage_and_deposits_from_a_remotely_piloted_aerial_application_system_using_various_nozzle_types
• Webinar (2024). Drift Reducing Agent Evaluation for Drone Spraying (Steve Li, Auburn University). https://www.youtube.com/watch?v=jILHMuyPVPA University of Minnesota: Drones: A Multifaceted Management Tool for Row Crop Agriculture. https://www.youtube.com/watch?v=UOzCqwj4zvE&list=PLOPc3IDYKqybSiG7WzV_N8wMghFRjAxKL&index=2

Content provided by DTN/Progressive Farmer.