Exploring the Accuracy of Drone-Applied Herbicide Treatments: What Growers Need to Know
Drone spraying is becoming a powerful tool for growers, but one question continues to come up—how accurate are drones when applying herbicides, especially at low water volumes?
A 2024 Corteva study and a new 2025 follow-up experiment by Jason Deveau (“Spray Guy”) provide valuable insight into how drones behave in real-world herbicide applications.
This article breaks down the research into a practical, easy-to-understand summary for growers, PCA’s, and land managers who want to understand drone accuracy, drift risk, and swath variability.
Why These Studies Matter
Herbicides are unforgiving compared to nutrients or fungicides. Even small gaps in coverage can leave weeds alive, while overlaps can burn crops or land boundaries.
These studies asked:
How wide is a drone’s actual spray swath compared to the programmed width?
Do swaths stay consistent, or do they vary across the field?
Does water volume impact herbicide performance?
Do faster flight speeds or different droplet sizes change swath width?
The findings are extremely relevant for operators and growers using drones on bare ground, rangeland, stubble, orchards, and field edges.
Key Finding #1: Water Volume Had Little Impact on Herbicide Efficacy
Corteva’s 2024 research compared hand-boom and drone-applied Clopyralid at multiple water volumes.
The surprising result:
Water volume did not significantly affect herbicide performance.
This reinforces what drone operators already see in the field—
herbicides often tolerate low-GPA applications as long as droplets reach the target.
Key Finding #2: Drone Swaths Were Often Wider Than Expected
Both studies revealed something important:
The actual treated area was larger than the programmed swath width.
The DJI T50 treated ~32% more area than planned
The DJI T100 treated ~40% more area than planned
Wider-than-expected swaths were partly driven by wind displacement and downwash
For growers, this means:
drones may achieve wider coverage than the controller shows
there is potential for off-target impacts near field margins
operators must be aware of drift risk even at low altitudes
Key Finding #3: Swath Width Was Not Always Consistent
Using NDVI-based burn mapping, researchers noticed that:
Swaths fluctuated along each flight line, sometimes wider, sometimes narrower.
This variation can create:
areas of overlap → higher-than-intended dose
areas of underlap → streaks or untreated strips
Experienced drone operators compensate with:
tighter swath spacing
correct droplet size for the task
swath overlap percentages validated through real-world testing
Key Finding #4: Droplet Size Influences Swath Width
The study tested spray qualities from fine (80 μm) to coarse (500 μm).
Results:
Fine droplets traveled farther, producing swaths up to 46% wider
Coarse droplets stayed tighter, reducing drift and swath width
Takeaway for growers:
Fine droplets improve coverage but increase drift risk
Coarse droplets are better for boundaries and high-drift environments
This is why drone operators carefully select droplet size based on:
product label
environmental conditions
target species
proximity to sensitive areas
Key Finding #5: The T100 Creates Wider Swaths Than the T50
Across all tests, the T100 consistently produced:
~15% wider swaths
more lateral displacement
Its larger frame, faster speeds, and stronger downwash likely contribute.
This matters because:
T100 operators may need tighter swath spacing
Field edges require extra caution
Droplet size selection becomes even more critical
Key Finding #6: Flight Speed Didn’t Consistently Change Swath Width
Against expectations, higher flight speeds did not reliably increase swath width for the T100.
A likely explanation is something called transitional lift:
At higher speeds (around 30–45 km/h), drones begin flying more like a helicopter in forward motion, reducing the downward rotor wash that normally influences spray movement.
This means:
downwash may be weaker at high speeds
drift behavior changes
swath patterns are not intuitive
Skilled operators adjust speed based on:
product type
droplet size
atmospheric stability
terrain and boundary proximity
What This Means for Growers
1. Drone herbicide applications can be highly effective.
Both studies confirmed strong weed control even at low water volumes.
2. Real-world swath width is often wider than expected.
Growers should work with operators who understand drift behavior and validate swath spacing.
3. Droplet size matters—a lot.
Fine droplets expand the swath; coarse droplets tighten it.
4. Edges, waterways, and sensitive crops require extra caution.
Experienced operators use special settings for boundary passes.
5. Not all drones behave the same.
The T100 has distinctly different downwash and drift characteristics compared to the T50. Operators must tune settings for each model.
The Bottom Line
These studies reinforce that drones are powerful, accurate spraying tools — when operated by trained, certified professionals who understand drift, droplet size, and swath behavior.
As drone technology evolves, herbicide performance will continue to improve, but growers benefit most when:
applications are planned carefully
swath spacing is validated
droplets are sized correctly
boundaries are respected
Drone spraying is not “just flying a sprayer.” It’s precision application — and accuracy matters.