Contents
Agriculture Spray and Drift

Drift Reduction Adjuvants for Agricultural Spray: A Strategy to Choose Drift Control Adjuvants and Drift Reduction Agents for Pesticide Spray Without Losing Coverage

Spray drift is driven mainly by fine droplets, nozzle choice and weather, so drift reduction must be proven with droplet sizing or wind tunnel tests. Surface tension and leaf contact angle checks keep each tank mix and adjuvant batch matched to the one that passed, and show whether a drift control adjuvant has cost you leaf wetting.

Who this is for: Adjuvant makers, agrochemical formulators and crop protection teams developing or supplying drift reduction adjuvants.

Where it fits: Alongside droplet size and wind tunnel testing: batch release, tank mix checks and leaf wetting checks.

What it does not do: It does not measure droplet size, driftable fines, extensional viscosity or field drift.

Method
Pendant drop surface tension and sessile drop contact angle
Standard
Does not run the ASTM D3825 fast bubble method; complements ASTM E2798 droplet sizing
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Farmer with a backpack sprayer spraying a rice field, with spray drifting across the crop
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
Read More
Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
Read More
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop
Why it matters

Why spray drift reduction matters

25% to over 90%

drift reduction bands in EPA's star ratings for drift reduction technologies, measured against a standard nozzle; at least 25% is needed for a rating.

US EPA, Drift Reduction Technology program (2021 archived page)

About 3,500

dicamba related incident reports in the 2021 season, with more than one million acres of soybeans allegedly damaged by off-target movement.

US EPA, dicamba incident report summary, 2021 growing season

Sources: US Environmental Protection Agency, EPA verified and rated drift reduction technologies (archived January 2021); US EPA, EPA releases summary of dicamba related incident reports from the 2021 growing season, December 2021. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this adjuvant check does and what it does not

A quick reference for adjuvant and crop protection teams checking fit before reading further.

Evidence Box

Problem this solves

Tank mixes and adjuvant batches that drift from the tested reference, and drift control adjuvants that reduce leaf wetting.

Standards

Drift reduction adjuvants are tested by droplet sizing, as in ASTM E2798. ASTM D3825 covers fast bubble dynamic surface tension, a method the Dropometer does not run.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

A European startup developing co-formulants for pesticides and fertilisers uses the Dropometer to study how its adjuvants wet leaves and lower surface tension.

Regulatory context

EPA rates drift reduction technologies from 25% to over 90% reduction against a standard nozzle, using droplet size or wind tunnel data.

Honest limit

Surface tension does not predict drift. Use it to keep batches consistent and to check wetting, not to claim drift reduction.

Who this is for

What drift reduction question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Adjuvant maker

Your drift reduction adjuvant passed droplet sizing. Each new batch must behave the same. A surface tension and leaf wetting check against the tested reference catches dosing, lot and water changes between sizing runs.

Some polymer drift retardants barely change surface tension; for those, check viscosity or repeat sizing.

Agrochemical formulator

You add a drift control agent to a herbicide or other pesticide formulation. Measuring leaf contact angle with and without it shows whether you have traded coverage for drift control.

Larger droplets drift less but can bounce more; check wetting on the target leaf.

Crop protection or stewardship team

You need a drift mitigation strategy for pest control that holds up in agricultural applications. Wetting checks complement nozzle selection, buffer zones and weather rules; they do not replace them.

Drift ratings come from droplet size or wind tunnel tests, not from surface tension.
Fit check

Is this the right test for your drift control program?

It helps for batch consistency and leaf wetting. It does not measure drift.

Good fit if

You release adjuvant or tank mix batches against a tested reference.
You need to know whether a drift reduction agent reduces leaf wetting.
Water hardness or tank mix partners change performance.
You set rates of non-ionic surfactants or another additive in a drift control adjuvant blend.
You want a fast lab check between droplet sizing runs.

Less relevant if

You need droplet size spectra or percent driftable fines.
You need extensional viscosity or shear degradation data.
You need surface tension at millisecond surface ages.
You need a drift reduction claim for a label.
Summary

How to choose drift reduction adjuvants

The answer in under a minute.

Prove drift reduction with droplet sizing or wind tunnel tests on the full tank mix and nozzle; most drift reduction adjuvants work by changing how the liquid breaks into droplets, not through surface tension. Then use surface tension and leaf contact angle to release each batch against the tested reference, and to check that the adjuvant has not reduced coverage.

The Dropometer surface tension and contact angle kit runs both checks; our surface tension measurement guide and article on why you need dynamic surface tension explain the methods. ASTM D3825 describes fast bubble dynamic surface tension, which the Dropometer does not run. A European agrochemical startup uses the Dropometer for adjuvant work. Our farming and agriscience guide covers the wider context.

Expert Quote

Expert perspective on surfactant rates

“

The critical micelle concentration is not a number you look up; it is where the surface-tension curve flattens, and the only honest way to know it is to measure it.

Dr. Alidad Amirfazli

Professor, Department of Mechanical Engineering, York University; Co-founder, Scientific Advisor, Droplet Lab

The problem

What drives spray drift and where adjuvants fit

Spray drift is the off-target movement of pesticide droplets or vapour away from the intended target during and after pesticide applications, in ground and aerial applications alike. It costs product, harms neighbouring crops and raises human health and environmental concerns: EPA received about 3,500 dicamba related incident reports in the 2021 season. Most drift comes from driftable fines, the fine particles and small spray droplet fraction that stays airborne. Their share depends mostly on the spray nozzle, spray equipment set up, pressure, boom height, flow rates and atmospheric conditions such as wind and temperature, the environmental conditions an applicator cannot control. Drift reduction adjuvants, also sold as drift control agents or deposition modifiers, aim to increase droplet size and the overall droplet size of the spray, reducing driftable fines, usually by changing how the liquid sheet breaks up at the nozzle, through polymers or emulsions, rather than through surface tension. That means a drift reduction claim needs droplet sizing or wind tunnel data. What surface tension and contact angle can do is keep each batch matched to the tested reference, and show whether a drift control strategy has reduced how well the spray solution wets the target.

Drift complaints or off-target damage near treated fields.
A new adjuvant batch behaves differently in the sprayer.
Coverage or efficacy falls after adding a drift control agent.
Performance changes with water source or tank mix partners.
Results from droplet sizing are not repeated in the next batch.
Troubleshooting

Why drift control fails and what to check

Why:

  • Fine spray nozzles and high pressure make more driftable fines than any adjuvant can fix.

How to detect:

  • Droplet size data show a high share of fine droplets; this is not a surface tension problem.

Corrective action:

  • Test coarser setups, such as air induction or extended range flat fan nozzles at the right pressure, and confirm the result by droplet sizing.

Why:

  • A wrong rate or a changed adjuvant lot changes the spray solution from the tested reference.

How to detect:

  • Surface tension at a fixed drop age differs from the reference mix, where the adjuvant contains surfactants.

Corrective action:

Check dosing and lot, then retest. Our guide to reproducible surface tension measurement covers fair comparisons.

Why:

  • Polymer drift retardants can lose effect after recirculation through pumps.

How to detect:

  • Droplet sizing after recirculation shows more fines; surface tension may not change at all.

Corrective action:

  • Test after the same recirculation the sprayer gives, and choose shear stable products.

Why:

  • Hard water and other products in the tank change how adjuvants, pesticide formulations and active ingredients behave.

How to detect:

  • Surface tension or leaf contact angle shifts with water source or tank mix.

Corrective action:

  • Test in field water with the real tank mix, and consider a water conditioning adjuvant.

Why:

  • Large droplets drift less but can bounce off waxy leaves and cover less of the leaf, so the target pest gets less product.

How to detect:

Contact angle on the target leaf rises after the drift control adjuvant is added. Our surfactant glossary entry explains how wetting partners help.

Corrective action:

  • Add or adjust a wetting partner, recheck leaf contact angle, and confirm retention in the spray chamber.

Not sure whether your batches match the tested reference?

Send the reference tank mix and a new batch, and we will compare them on a call.

Book a 15 minute demo
Quality records

What a tank mix and adjuvant record contains

Each check produces a record you can file with the adjuvant batch or tank mix. These records can sit beside your droplet sizing and wind tunnel reports in your existing quality records.

Mix identity

Pesticide product, drift reduction adjuvant and rate, tank mix partners and water source.

Reference

The reference mix and the droplet size or wind tunnel report it passed.

Method settings

Needle size, drop ages, drop volume, contact angle read time and recirculation.

Readings

Surface tension at each drop age and contact angle on the target leaf.

Decision

Release, retest or hold, and whether droplet sizing must be repeated.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure in a drift reduction program

Batch match

Surface tension against the tested reference

Why it matters: It shows whether a batch or tank mix differs from the one that passed droplet sizing.

How to interpret: Compare at the same drop ages and water, measured the same day. Set bands from your own reference.

When it is not enough: Polymer drift retardants may not change surface tension.

Speed

Surface tension at several drop ages

Why it matters: It shows how fast surfactants in the blend act.

How to interpret: Compare curves, not single points.

When it is not enough: Pendant drop starts from about a second; atomization happens in milliseconds.

Coverage

Contact angle on the target leaf

Why it matters: It shows whether the drift control adjuvant reduced wetting.

How to interpret: Compare with and without the adjuvant; a rise means less coverage per droplet.

When it is not enough: It does not show bounce at impact.

Drift

Droplet size spectrum and fines, measured separately

Why it matters: This is what actually decides drift.

How to interpret: Use laser diffraction or wind tunnel data, as in ASTM E2798.

When it is not enough: The Dropometer does not measure it.

Validation

Validated measurement approach for adjuvant checks

How the Dropometer itself has been validated, and where customers have used it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer evidence in agrochemicals

A European startup developing co-formulants for pesticides and fertilisers bought a Dropometer to study how its adjuvants wet leaves and lower surface tension. Its water first read about 60 mN/m; a live call traced it to the needle size used for calibration, and the team now reads 71 mN/m.

Read the case study
QC Protocol

How to keep drift reduction adjuvant batches consistent

Six steps for one product, adjuvant and nozzle setup. Repeat when any of them changes.

1

Prove drift reduction first

Size droplets or run wind tunnel tests on the full tank mix and nozzle, and keep that reference mix.

2

Check calibration

Measure pure water first; it should read close to 72 mN/m at room temperature.

3

Baseline the reference

Measure the reference mix's surface tension at several drop ages and its contact angle on the target leaf.

4

Check each batch

Mix each batch in field water with the same recirculation, and measure it the same way.

5

Release, retest or resize

Release batches inside the bands; repeat droplet sizing when a batch falls outside them.

6

Check coverage

Compare leaf contact angle with and without the drift control adjuvant. Using these adjuvants should not cost coverage; our page on improving spray coverage on leaves covers the wetting side.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the tank mix and adjuvant QC SOP

A two page SOP you can adapt for your adjuvant and tank mix, with the method lock, gates against a tested reference, a troubleshooting table and a record sheet.

Surface tension measurement with the Dropometer

Example output

Example tank mix batch log against a tested reference

Example data only. Your values and gates will differ and must come from your own references.

How to read this log

Example gates: surface tension within 2 mN/m of the reference at 1 s, and leaf contact angle within 8°. Batch 2 used a new adjuvant lot and fell outside both, so droplet sizing is repeated. The mix without the drift adjuvant reads almost the same, which shows surface tension cannot confirm this adjuvant's dose.

Sessile drop contact angle measurement: DI Water on Glass, left contact angle 44.9°, right 45.7°

Example tank mix batch log

Mix Change Surface tension at 1 s (mN/m) At 30 s (mN/m) Contact angle on leaf (°) Result
Reference mix Passed droplet sizing 38.0 33.0 72 Reference
Batch 1 None 38.4 33.2 73 Release
Batch 2 New adjuvant lot 41.9 36.5 84 Hold, resize
Batch 3 Hard field water 40.2 35.0 80 Retest
Mix without drift adjuvant For comparison 37.5 32.8 70 Information

Example data, not customer data. Herbicide tank mix with a drift reduction adjuvant, at 22 °C; surface tension by pendant drop at 1 s and 30 s; contact angle on waxy weed leaves.

Signal order

The order to check signals when drift control slips

Check these in order. Each one rules out a cause before you look at the next.

1

Nozzle, pressure and weather

The biggest drift drivers, checked against the application plan.

2

Droplet size data

Fines from sizing or wind tunnel tests for the actual tank mix.

3

Batch surface tension

Shows whether the batch matches the tested reference.

4

Leaf contact angle

Shows whether coverage was traded for drift control.

5

Water and tank mix

Hardness, pH and partners that change the spray solution.

FAQ

Common questions about drift reduction adjuvants

Questions adjuvant and crop protection teams ask about drift control and adjuvant selection.

How do drift reduction adjuvants work?

Most increase droplet size and cut driftable fines by changing how the liquid sheet breaks up at the nozzle, using polymers that raise extensional viscosity or oil emulsions. They work best with the right nozzle and pressure, and their effect must be shown with droplet size data for the full tank mix.

Does lowering surface tension reduce spray drift?

Not reliably. Droplet size depends mostly on the nozzle, pressure and how the liquid sheet breaks up, and the effect of surfactants on fines depends on the nozzle. Surface tension matters more for how droplets wet the leaf than for drift. That is why we position the Dropometer for batch consistency and coverage checks, not as a drift test.

What do EPA drift reduction ratings mean?

EPA rates drift reduction technologies by how much they cut potential spray drift against a standard nozzle: 1 star for 25 to 50%, 2 stars for 51 to 75%, 3 stars for 76 to 90% and 4 stars for more than 90%. Ratings come from test data on droplet size or drift.

Can a drift control adjuvant reduce coverage?

It can. Larger droplets help reduce drift and reducing spray drift matters, but they may bounce off waxy leaves or cover less of the leaf. Measure contact angle on the target leaf with and without the adjuvant, and add a wetting partner if needed.

Which standards apply?

ASTM E2798 is the test method for drift reduction adjuvants by droplet size spectra and fines. ASTM E1519 sets adjuvant terminology. ASTM D3825 covers fast bubble dynamic surface tension; the Dropometer does not run that method.

How do nozzles compare with adjuvants?

Nozzle choice and pressure usually matter more than the adjuvant. USDA ARS work found no drift difference between air induction and conventional flat fan nozzles at the same orifice size and flow rate, so test the setup you will use.

Which instrument do we need?

For drift itself, a laser diffraction droplet sizer or wind tunnel. For batch and wetting checks, pendant drop surface tension and contact angle in one kit. For millisecond dynamic surface tension, see our guide to the best tensiometer for dynamic surface tension.

Business impact

What changes when you add batch and wetting checks to drift control

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with batch and wetting checks

Metric Before Dropometer With Dropometer Indicative Benchmark
Batch consistency Droplet sizing only, rarely Surface tension check on every batch No published benchmark; track on your own batches
Drift reduction proof Droplet sizing or wind tunnel Unchanged; still needed EPA star ratings from 25% to over 90% reduction (EPA DRT program)
Coverage after drift control Assumed Leaf contact angle with and without the adjuvant No published benchmark; track on your own products
Off-target movement risk Managed by nozzle and weather rules Plus consistent batches About 3,500 dicamba incident reports in 2021 (EPA)

See the check on your own tank mix

Send the reference mix and a new batch. We will show the comparison on a call.

Book a 15 minute demo

Estimate saved development work

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Drift adjuvant R&D cost estimate

Estimate saved development work and lab cost.

Each Dropometer unit is $5,000; the default models 1 unit.
Your own number of candidate adjuvants per year.
Your own material and preparation cost per candidate.
Your own hours to prepare, measure and analyse one candidate.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Iterations saved / month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What surface tension cannot tell you about drift

Honest limits, so you know when to reach for another test.

It does not measure droplet size or driftable fines.
Polymer drift retardants may not change surface tension at all.
Pendant drop does not reach millisecond surface ages.
It does not measure extensional viscosity or shear degradation.
Calibrate with pure water; a wrong needle size gives wrong values.
A matching batch reading does not replace a drift claim from sizing data.

Surface tension and contact angle keep batches consistent and check wetting. Drift reduction, droplet size, extensional viscosity, shear stability and field drift need droplet sizing, wind tunnel and field tests.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related spray workflows

These pages cover the standards, the customer evidence and the leaf wetting side of spray performance.

Standard

ASTM D3825

Dynamic surface tension by the fast bubble technique.

View standard

Case study

European agrochemical startup

Adjuvant wetting work and a calibration fix.

Read case study

Instrument

Dropometer

Pendant drop surface tension and contact angle in one kit.

View product

Related use case

Agriculture spray and leaf wetting

All spray, leaf wetting and drift use cases in one place.

View Page

Related use case

Improve leaf coverage

Droplet size, retention and wetting on leaves.

View Page

Related use case

Wettability alteration screening

Screen surfactants and chemicals by how they change wetting.

View Page

Guide

Farming and agriscience guide

Surface science for agriculture.

Read guide

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
US Environmental Protection Agency. EPA verified and rated drift reduction technologies. Archived page, January 2021. https://19january2021snapshot.epa.gov/reducing-pesticide-drift/epa-verified-and-rated-drift-reduction-technologies_.html
2.
US Environmental Protection Agency. EPA releases summary of dicamba related incident reports from the 2021 growing season. December 2021. https://www.epa.gov/pesticides/epa-releases-summary-dicamba-related-incident-reports-2021-growing-season
3.
USDA Agricultural Research Service, Wooster, Ohio. Investigation of drift reduction potential with air induction nozzles and conventional nozzles. https://www.ars.usda.gov/midwest-area/wooster-oh/application-technology-research/engineering/investigation-of-drift-reduction-potential-with-air-induction-nozzles-and-conventional-nozzles
4.
ASTM D3825. Standard test method for dynamic surface tension by the fast bubble technique. https://dropletlab.com/industry-standards/astm-d3825-90/
5.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
6.

Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects.

https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
7.
Droplet Lab validation papers
8.
Customer publications that cite the Dropometer
9.
Agrochemical startup case study
10.
Why you need dynamic surface tension