Spray Drift – What causes it and how to avoid it Pesticide Applicator Certification For: Professional Development Solutions Tom Wolf AgriMetrix Research and Training Saskatoon, SK agrimetrix@gmail.com @Nozzle_Guy 1 1

Drift – The Ambassador of Spraying

3 Es of Pesticide Application Application Goals 3 Es of Pesticide Application Effective Efficient Environmental Norman Morgan 2 2

Airborne movement of droplets or vapours from the treated area Spray Drift Airborne movement of droplets or vapours from the treated area Droplet drift usually occurs within minutes of the application, vapour drift can occur minutes or days after application

On-Swath Deposit Low boom Slow speed High boom Fast speed

Drift Spray Accountancy 100% 1.7% 2 m 5-120 m 5 m 1 m 82% 10% 5% 1% 0.3% On Target Off Target

45 M kg x 80% sprayed x 1.7% airborne loss The Size of the Problem 45 M kg x 80% sprayed x 1.7% airborne loss = 612,000 kg

Drift Patterns

Deposit Patterns

Drift Causes

Small Droplets Wind Drift!

Factors Involved in Spray Drift Wind speed Atmospheric turbulence - thermal - mechanical Droplet size Droplet velocity - sprayer type - pressure Initial size - sprayer type - nozzle type, size - pressure - formulation Rate of evaporation - temperature - RH Transit time - velocity - boom height Droplet drift

What Causes Drift? Low Energy Exposure to Force Movement

Exposure to Force Low Energy Strategy Increase size Increase velocity e.g. low drift nozzles, air assist Exposure to Force Protect Decrease exposure time e.g. shrouds, low booms, slow travel

Areas of unequal pressure create vortices which remove small droplets from the spray cloud

Focus is droplet size and boom height Reducing the Problem Nozzle selection Sprayer settings Focus is droplet size and boom height

Drift Potential Drift Potential 50 80015 11003 40 75 psi 30 40 psi Spray Pressure Fan Angle Flow Rate Nozzle Type 50 80015 11003 40 75 psi 30 40 psi 8003 8003 ER8003 Drift Potential 20 20 psi 8006 SR8003 10 DR8003

Droplet Size Distributions Let’s talk about how we describe droplet size. Here is a typical distribution of spray volume in an agricultural spray, using a conventional nozzle (red). Note that the spray contains both very small (10 µm) and very large (1000 µm) droplets. The majority of the spray volume is in intermediate sized droplets between 200 and 500 µm When we lower the pressure (or change to a low-drift nozzle), we still retain the same large span of droplet diameters ranging from 10 to 1000 µm (blue bars). But now, the distribution has shifted to the right. This means less volume in small droplets (less drift), more volume in large droplets. The majority of the dose remains in the middle region, but more of it is in the larger droplets. As long as we don’t go too far with coarseness, we’re OK. All low-drift nozzles operate on the same basic principle (internal pressure drop creating larger droplets). 22

Spray Quality

Field Tests

Flexi-Coil Field Sprayer Application volume = 100 L/ha Travel speed = 13 km/h XR8003, 40 psi AI110025, 58 psi

Medium 26

Very Coarse At 40 psi, spray quality is starting to be good for general weed control 27

Gregson High-Clearance Sprayer Application volume = 100 L/ha Travel speed = 22.5 km/h TT11005, 40 psi AI11004, 64 psi

Boom Height Drift potential doubles for higher boom Use auto boom-height controller

“Auto-Boom”

Reduced Spray Pressure? Conventional flat fans 20 - 40 psi Pre-orifice 30 - 50 psi Air-Induced 40 – 60 psi (low-pressure type) 60 – 80 psi (high pressure type) Ensure that patterns are optimal

Droplet Velocity (Energy)

Droplet Velocity Distributions Spray velocity tends to slow down with coarser sprays, due to the lower internal pressures of these nozzles. This means that large drops from a low-drift nozzle are more easily retained than the large drops from conventional nozzles – a good thing. 35

Principle of HARDI TWIN air assistance

Air Off Air On

Drift- at various wind speeds (data from Hardi)

Little Drift Lots of Drift

Models and Regulations Courtesy of Paul Miller, SRI

New Buffer Zone Label Language Untreated (Buffer Zone) 20 m Conventional application 15 m Low-drift application untreated 5 m Very low-drift application untreated

“Do not apply with spray droplets smaller than ASAE medium classification” “…When using a shroud, BZ can be reduced by 70%...”

Buffer Zone Calculator

http://www.hc-sc.gc.ca/cps-spc/pest/agri-commerce/drift-derive/index-eng.php

Example

Atmospheric Conditions Courtesy George Ramsey, DuPont

Daily Wind Pattern Time of day (h) Wind speed at 1 m height (m/s) 8 7 6 5 4 Wind speed at 1 m height (m/s) 3 2 1 4 8 12 16 20 24 Time of day (h)

Mechanical Turbulence

Thermal Turbulence

Inversion Conditions Dispersion Spray cloud disperses, moving upward and downwind Unstable (Desirable normal daytime conditions) Warm Soil Inversion Conditions Disapppears after sunrise and 2-3 degree increase in temperature. Warm, still air Spray cloud hangs over treated area in high concentration Stable (inversion) Cold air - dense, still Cold soil

Unstable Stable (Inversion) Height Temperature Height Temperature

Height Temperature 3 pm 11 pm 3 am 5 am 7 am 8 am 9 am 3 pm Sunset 10 pm 3 am 5 am Sunrise 5 am 7 am 8 am 9 am 3 pm Height Temperature

3 pm 11 pm Sunset 10 pm 3 am 5 am Sunrise 5 am 7 am 8 am 9 am 3 pm

Wind Calm conditions not well suited for spraying unpredictable wind direction sometimes mistaken for inversions Low, steady winds ideal Predictable direction Dilution of spray cloud High winds increase total loss, but do not always increase deposits

Delta T (droplet evaporation)

Most Important Factors Governing Drift Trained, conscientious operator Communication / Relationships Weather Conditions Spray Quality Shrouds Boom Height Travel Speed