refinement of spray drift estimates for non-target terrestrial plant

Refinement of Spray Drift Estimates for Non-Target Terrestrial Plant Risk

April 23, 2015

Dan Dyer - on Behalf of the CLA Spray Drift Issue Management Team

Tier-1 Ground Spray Model, AgDRIFT

• AgDRIFT produces unreasonably conservative

drift estimates

Especially conservative at far distance from edge of field

Low endpoints associated with endangered non-target

terrestrial plants often fall in this far-distance range

Leads to unreasonable, impractical buffer distance

• AgDRIFT is not representative of current spray

technology

Spray Drift Task Force (SDTF) dataset (1992 and 1993),

used old nozzle technology

No drift reducing nozzles (drift reducing technology)

No low drift air-induction/chamber nozzles

AgDRIFT – Overestimation of Drift

• Limited refinement capabilities

90th Percentile of lumped data

“Very fine to fine” or “fine to

medium/coarse”

High and low wind speed

Not possible to select drift data in

compliance with proposed best

management practices (labeling)

Spray quality: e.g. medium, coarse,

very coarse, etc.

Wind speed: e.g. <10 mph

Endangered Species Drift Assessment for “Herbicide”

• Example of ongoing endangered non-target

terrestrial plant (NTTP) drift assessment

Endpoint: 0.05% of application rate (for most

sensitive species)

Label restrictions:

“coarse or coarser” spray quality

<10 mph wind speed

• AgDRIFT: 604-ft proximity distance

fine to medium/coarse nozzle

low boom height

• Impractical potential buffer distances

Higher Tier Drift Refinement

• REGDISP -- model built on AGDISP (v. 8.26)

• US Forestry Service made code available to Industry

• uses current EPA accepted version of AGDISP

• desire to keep the mechanistic ground model

• No changes to existing AGDISP code existing

• Better interface for AGDISP calculators

• Enables parsing of data and addition of data

• Addresses issues with AgDRIFT

Herbicide Higher Tier Drift Refinement

• Refinement based on Agriculture and Agri-Food

Canada (AAFC) dataset (2000, 2011)

Drift deposition curves selected based on spray quality

and wind speed

Drift reduction nozzles (e.g., air-induction), in addition to

standard flat fan

Spray boom height between 24” and 35” above ground

Wind speed from 5 to 19 mph

Regression equations taken from REGDISP

• Methodology

Five coarse to extra-coarse nozzles in AAFC dataset

Multiple datasets per nozzle/wind speed

Proximity distances calculated from individual

deposition curves for different wind speeds and boom

heights based on the NTTP endpoint

Data grouped for each nozzle separately and according

to wind speeds (<10 mph or >10 mph)

Averages and total ranges of proximity distances

Herbicide Higher Tier Drift Refinement

30-113 ft (<10 mph) ; 80-176 ft (>10 mph)

6930

87113 103

133

80116

156176

0

50

100

150

200

250

AIXR110-025 DR110-05 AI110025 TT11005 AI11004

Pro

xim

ity

Dis

tan

ce (

ft)

Terrestrial Spray Drift Proximity Distance from Edge-of-Field(0.05% Deposition of Application Rate)

Wind speed <10 mph Wind speed >10 mph

Refinement based on AAFC dataset

AgDRIFT: 604 ft

Higher Tier Refinement - Field Study

Field Study - to further

refine drift estimates

and verify REGDISP

refinement

Spray length: ~600 ft

Spray width: ~247.5 ft

(3 passes x 82.5 ft)

Deposition samplers:

300 cm2 cellulose

pad

3, 6, 15, 30, 60, 120,

240, 360, 450 ft

downwind

Commercial product

and sprayer

Analyze for herbicide

Deposition

Samplers

Drift Deposition – Field Study

• Field data and curve fit (example)

0.000%

0.001%

0.010%

0.100%

1.000%

10.000%

100.000%

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450

Per

cen

t o

f A

pp

licat

ion

Rat

e

Downwind Distance (ft)

TT11003 (37 psi)7.4 – 7.8 mph

Transect A

Transect B

Transect C

Curve Fit

0.0001%

0.0010%

0.0100%

0.1000%

1.0000%

10.0000%

100.0000%

0 15 30 45 60 75 90 105 120 135 150

Pe

rce

nt

of

Ap

pli

cati

on

Ra

te


Proximity Distance (based on Drift Trials)

AIXR11002 (10 mph)

TT11003 (<10 mph)

AIXR11002 (<10 mph)

Endpoint

Drift Deposition – Field Study

AIXR11002 (10 mph): 68 ft

TT11003 (<10 mph): 64 ft

AIXR11002 (<10 mph): 45 ft

REGDISP: 30 - 113 ft

0.0001%

0.0010%

0.0100%

0.1000%

1.0000%

10.0000%

100.0000%

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600

Per

cen

t o

f A

pp

licat

ion

Rat

e


Proximity Distance

AIXR11002 (10 mph)

TT11003 (<10 mph)

AIXR11002 (<10 mph)

AgDRIFT (6 swath; 270 ft)

AgDRIFT (20 swath)

Endpoint

Field Drift vs REGDISP vs AgDRIFT

Field Study 45 - 68 ft

REGDISP 30 - 113 ft

AgDRIFT (6 swath) 322 ft

AgDRIFT (20 swath) 604 ft

Summary

• REGDISP allows for conservative, higher tier drift

modeling, necessary to refine unrealistic and impractical

drift estimates from AGDRIFT.

Conservative nature of REGDISP verified with results of field study

• REGDISP is especially critical/useful for NTTP

endangered species assessments, where endpoint may

be low.

Summary

• REGDISP is valuable tool, and necessary step in a tiered

approach to drift refinement based on product best

management practices

Spray quality/nozzle type, wind speed, etc.

• Field drift studies should not be prerequisite for use of

REGDISP

field studies are appropriate higher tier refinement, when

necessary

Thank you

refinement of spray drift estimates for non-target terrestrial plant

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