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Effects on pesticide spray drift of the physicochemical

Precision Agric(2009)10:409–420

DOI10.1007/s11119-008-9089-6

Effects on pesticide spray drift of the physicochemical properties of the spray liquid

Mieke De Schampheleire?David Nuyttens?Katrijn Baetens?

Wim Cornelis?Donald Gabriels?Pieter Spanoghe

Published online:31October2008

óSpringer Science+Business Media,LLC2008

Abstract This research was on the effect of the physicochemical properties of the spray liquid on pesticide spray drift.Ten pesticide spray liquids with various physicochemical properties were selected for study.Some of these spray liquids were also examined with the addition of a polymer drift-retardant.In the?rst part,laboratory tests were performed to measure surface tension,viscosity,evaporation rate and density of the spray liquids.Sub-sequently,drift experiments were performed in a wind tunnel.From the results it was found that the dynamic surface tension is a major drift-determining factor,and also that the addition of a polymer drift-retardant can reduce drift signi?cantly by increasing the viscosity.Drift reduction was found to be less effective with spray liquids of emulsi?able and suspendable formulation types than with spray liquids of water-dispersible granules and powders. Keywords Spray driftáPesticideáPhysicochemical propertiesáSurface tensionáViscosity

Introduction

Spray drift is de?ned as the quantity of plant protection product that is de?ected out of the treated area by air currents at the moment of spray application.Spray drift is affected by M.De Schampheleire(&)áP.Spanoghe

Department of Crop Protection,Ghent University,Coupure Links653,9000Gent,Belgium

e-mail:Mieke.DeSchampheleire@UGent.be

D.Nuyttens

Agricultural and Fishery Research Institute(ILVO),Burg.Van Gansberghelaan115,

9820Merelbeke,Belgium

K.Baetens

Department of Agro-Engineering and Economics,Catolic University of Leuven,

de Croylaan42,3001Leuven,Belgium

W.CornelisáD.Gabriels

Department of Soil Management and Soil Care,Ghent University,Coupure Links653,

9000Gent,Belgium

Table1Physicochemical classes of commercial pesticide formulations

Class Physical appearance Chemical composition

Emulsi?able concentrate(EC)Emulsion Co-solvents,surfactants Suspendable concentrate(SC)Suspension Surfactants,anti-foaming agents,

antifreeze agents,thickeners,binders Soluble liquid(SL)Liquid Surfactants,buffers,anti-foamers,?llers Water-dispersible granules(WG)Solid Binders,surfactants,anti-foamers,?llers Water-dispersible powder(WP)Solid Surfactants,stabilisers,anti-foamers

four main factors:weather conditions,spray application technique,characteristics of the surroundings and physicochemical properties of the spray liquid.Although research has been done on the in?uence of weather conditions and the spray application technique,little research has been done on the in?uence of physicochemical parameters on drift,probably because of the complex nature of the in?uence.This research focused on the importance of physicochemical properties(surface tension,viscosity,evaporation rate and density)of spray liquids on drift.

Most researchers who have examined the drift-reducing effects of adjuvants have used solutions of the adjuvant in water,even though it is accepted that it is not the physico-chemical properties of the adjuvant itself but the physicochemical characteristics of the complete spray mixture(pesticide formulation?adjuvant)that are drift-determining.We have used adjuvant/formulation combinations rather than adjuvant/water.

Commercial pesticide formulations can be subdivided into?ve important classes (Table1),according to their physical appearance and chemical composition(Spanoghe 2005).

It is expected that the chemical composition,and hence the class,has an in?uence on the physicochemical properties,which can affect droplet size and,therefore,spray drift.These physicochemical properties are viscosity,surface tension,density and evaporation rate of the?uid.

Materials and methods

Pesticide formulations and spray liquids

Ten commercial pesticide formulations,two of each type listed in Table1,were selected for experimentation(Table2),based on ease of detection with chromatography and the low toxicity of their active ingredients,except for Lannateò,which contains the active ingredient methomyl.Methomyl has a high mammalian toxicity,the acute oral LD50for male rats is34mg kg-1and for female rats it is30mg kg-1(Tomlin2006).

An overview of the commercial products,their active ingredient compositions,and the spray liquids that were formulated with them,is given in Table2.The spray liquids were prepared with tap-water according to the guide-lines of the manufacturers.

Polymeric adjuvants,called‘drift-retardants’,can be added to the spray liquid to increase the viscosity of the spray liquid and to reduce drift.Performances of the spray liquids of Tiltò,Ronilan SCò,Euparen Multiòand Paraatòwere also measured with the addition in0.1%w/w of the adjuvant AgRHO DR-2000ò,a powder that contains99%of the synthetic polymer polyacrylamide(PAM),the structure of which is given in Table2.

Physicochemical properties of the spray liquids

All of the physicochemical measurements,described below,were performed at a constant room temperature of 19±1°C.They were repeated three times.

Evaporation rate

The evaporation rates v were measured with the shape analysis camera of a drop tensiometer (Tracker I.T.Concept).A droplet (5l m diameter)was formed at the tip of the needle.The droplet surface area was determined each second for 5min with the shape analysis camera.From the surface areas,the droplet volumes were calculated.These volumes were used to calculate the evaporation rates v (nl s -1)of the droplets.All the measurements were performed in a closed cabin with still air,with a relative air humidity of 40±5%.Density

The densities q (kg l -1)of the spray liquids were determined by weighing a volume of 250ml of the liquid.

Extensional viscosity

The viscosities of the spray liquids,upon the addition of the adjuvant AgRHO DR-2000ò,were measured as extensional viscosities E =(t liquid ?AgRHO )/t liquid where t liquid is the ?ow time for the spray liquid,and t liquid ?AgRHO is the ?ow time of the spray liquid with AgRHO DR-2000òadded,between the upper and the lower mark of a glass capillary.This viscosity meter was constructed according to the standard ASTM E2408-04(2006).Surface tension

The surface tensions of the spray liquids were measured as dynamic surface tension (DST)(mN m -1)using the drop mass method with the set-up of Spanoghe (2005).A cylindrical capillary is hung vertically above a recipient beaker,which is placed on a balance.The liquid is pumped through the capillary at a constant,calibrated ?ow rate with a titrator

Table 2Commercial products and spray liquid formulations

Commercial product

Spray liquid AgRHO DR-2000òTilt ò

250g l -1propiconazole 2.5ml l -

1Cytox ò

100g l -1cypermethrin 10ml l -1Ronilan SC ò

500g l -1vinclozolin 10ml l -1Pyrus 400SC ò

400g l -1pyrimethanil 5ml l -1Caddy 100SL ò

100g l -1cyproconazole 0.6ml l -1Lannate 20SL ò

200g l -1methomyl 0.6ml l -1Euparen Multi ò

50%tolyl?uanid 1.5g l -1Chorus ò

50%cyprodinil 1.5g l -1Paraat ò

50%dimethomorph 0.4g l -1Kerb 50ò50%propyzamide 3g l -1

(autoburette).The volume of the droplet that is formed at the tip of the capillary,before the droplet falls,depends on the DST of the liquid.Liquids with high DST will form large droplets.The balance is connected to a computer that monitors the mass of the recipient. The DST can be calculated from the droplet mass with the equation DST=(gámáF)/R, where g is the gravitational force constant(9.81m s-2),m the mass of the droplet(kg),F a correction factor according to Henderson and Micale(1993)and R the outer radius of the capillary(m).

Wind tunnel experiments

Wind tunnel experiments were conducted in the International Centre of Eremology(I.C.E.) at Ghent University.The wind tunnel set-up is illustrated in Fig.1.

The I.C.E.wind tunnel is a closed-circuit type.Air?ow is generated by an axial fan, with adjustable blades whose pitch angle can be adjusted by means of a compressor to control the wind speed.At the entrance to the working area,the minimum free-stream wind speed that can be obtained is6.5m s-1.However wind speed can be further reduced by placing obstacles between the fan and the working area.An extra screen was placed between the fan and the working area to reduce the wind speed to4m s-1at ground level.

A detailed description of the wind tunnel is given by Gabriels et al.(1997).

Wind tunnel measurements were performed with the ten formulated spray liquids and with four of the ten spray liquids(Tiltò,Ronilan SCò,Euparen Multiòand Paraatò)to which0.1%w/w of the adjuvant AgRHO DR-2000òwas added.

Each wind tunnel experiment was repeated three times,using the set-up of Brusselman et al.(2005).An ISO Hardi FF11003nozzle,pointing downwards,was?xed at a height of 0.5m.At this height the wind speed had a value of3.4–3.5m s-1.The temperature and the relative air humidity were kept constant at18–20°C and45–55%.The sprayings were performed for15s at a constant spray pressure of0.3MPa.Plastic drains were incorpo-rated in the false bottom of the tunnel at distances of0.25,0.35,0.50,0.75,1,1.25,1.75, 2.25,3.5,4.65and6m from the spray nozzle.Filter paper slips(1m90.03m)were placed in these drains as collectors.The collector set-up is illustrated in Fig.2.

The collector slips were retrieved immediately after spraying and extracted with200ml of organic solvent(hexane,acetone or methanol)with suf?cient solubility for the active ingredients of the various spray liquids.Hexane was used for the extraction of

Fig.1Schematic view of the wind tunnel of the I.C.E

pyrimethanil,vinclozolin,cypermethrin,propiconazole,cyprodinil,tolyl?uanid,propyza-mide.Acetone was used for the extraction of dimethomorph.Methanol was used for the cyproconazole and methomyl.

The hexane and acetone fractions were dried over Na 2SO 4and the fractions were analysed with GC–MS or GC–ECD.The methanol fractions with cyproconazole and methomyl were analysed with HPLC.

Table 3gives an overview of the methods used for the different samples.Pesticide residues were quanti?ed by comparison with standards.

GC–MS was used for the detection of pyrimethanil,cyprodinil,tolyl?uanid,dim-ethomorph and propyzamide.The chromatographic analysis was performed with an Agilent 6890GC equipped with a 5973inert MSD.An HP-5MS capillary column (30m 90.25mm i.d.,0.25l m ?lm thickness,J&W Scienti?c,USA)was used and the oven program was as follows:70°C during 2min as initial temperature,a 25°C min -1ramp to 150°C,a 3°C min -1ramp to 200°C,an 8°C min -1ramp to 280°C,and 10min at 280°C.A split/splitless injector was used in the splitless mode (2min purge

time,Fig.2Set-up for drift measurements in the wind tunnel

Table 3Extraction recoveries and chromatography characteristics of the active ingredients

a.i.

Extraction recovery (%)Method Isomers Solvent delay (min)RT (min)Ions (m /z )Pyrimethanil

83.2GC–MS –10.0014.13198and 199Vinclozolin

90.5GC–ECD ––10.93–Cypermethrin 78.0GC–ECD a -isomer

–19.45–

b -isomer

19.56h -isomer

19.64f -isomer

19.68Propiconazole

80.4GC–ECD ––9.11–Cyprodinil

90.3GC–MS – 3.2020.78210and 224Tolyl?uanid

86.2GC–MS –15.0021.22137and 238Dimethomorph

83.6GC–MS E-isomer 30.0036.87301and 387Z-isomer 37.65Propyzamide

89.9GC–MS –8.5014.13173and 175Cyproconazole

78.9HPLC 2isomers – 3.63–3.87Methomyl 71.9HPLC –– 4.96–

50ml min-1purge?ow).The carrier gas was helium with a constant column head pressure of137kPa.The injector and transfer line temperatures were280and250°C, respectively.One microlitre of sample was injected.Mass detection was performed in the single ion monitoring(SIM)mode after a solvent delay(ionization energy for electron impact was70eV).The solvent delays,the retention times and the selected ions used for detection and quanti?cation are given in Table3.The ions were selected from the frag-ments with the highest m/z values and strongest signals,which are highly speci?c for each compound.

Dimethomorph consisted of two isomers and the sum of the isomers was taken into account for the calculations.

GC–ECD was used for the detection of vinclozolin,cypermethrin and propiconazole. The chromatographic analysis was performed with an Agilent6890GC equipped with a micro G1533A ECD.An HP-5MS capillary column(30m90.25mm i.d.,0.25l m?lm thickness,J&W Scienti?c,USA)was used and the oven program was as follows:30°C as initial temperature,a30°C min-1ramp to180°C,a3°C min-1ramp to205°C,hold for 4min at205°C,a20°C min-1ramp to290°C,and hold for8min at290°C.A split/ splitless injector was used in the splitless mode(2min purge time,73.5ml min-1purge ?ow).The carrier gas was helium with a constant column head pressure of103kPa.The injector temperature was280°C.One microlitre of sample was injected and detection was with an electron capture detector(ECD).

Cypermethrin consisted of four isomers and the sum of the isomers was taken into account for the calculations.

HPLC was used for the detection of cyproconazole and methomyl.HPLC–DAD UV analysis was with a Finnigan Surveyor HPLC(Thermo Electron Corporation;Waltham, MA,USA)equipped with a gradient pump,a degasser,an autosampler,and a diode array detector(DAD).The analytical column used was an Alltima HP C18EPS3l m 150mm93.0mm(Alltech Associates Inc.,Deer?eld,IL,USA).The detector was set at a wavelength of208nm.The mobile phase consisted of an acetonitrile(solvent A)—0.1% H3PO4in water(solvent B)solution at a linear gradient from32%to60%of solvent A in 4min and in4min from60%to35%of solvent A,with4min for column equilibration. Flow rate was0.7ml min-1and the volume injected was10l l.Under these conditions, the retention time for methomyl was4.96min.

Cyproconazole consisted of two isomers with retention times of3.63and3.87min,and the sum of the isomers was taken into account for the calculations.

The concentrations of the active ingredients,found by GC or HPLC,were corrected for recovery.For this,a?lterpaper was spiked with1ml of the spray tank solution.The paper was extracted with200ml hexane,acetone or MeOH and,after drying over Na2SO4 (hexane and acetone),the organic fractions were analysed with GC or HPLC.The recovery ef?ciency was calculated as the detected amount of active ingredient divided by the amount spiked on it.Drift was expressed as percentages of the amounts sprayed.

Correlations and drift reduction potentials

Correlations between the physicochemical parameters v,q and DST and the drift data were calculated for each drift distance by plotting the drift percentages(y-axis)against the physicochemical parameter(x-axis)for the ten spray liquids.

The drift reduction potential(DRP)of the adjuvant AgRHO DR-2000òfor the different formulations was calculated according to Eq.1,

DRPe%T?100?P x?6

x?0:25

%driftexTáD xà

P x?6

x?0:25

%drift DRexTáD x

P x?6

x?0:25

%driftexTáD x

e1T

with x the drift distance(0.25–6m),%drift(x)the drift percentage of the spray liquid at distance x,and%drift DR(x)the drift percentage of the spray liquid with drift-reducer added,at distance x.

Results

Physicochemical properties of the spray liquids

The results for the evaporation rates v(nl s-1)and for the densities q(kg l-1)of the ten spray liquids,with and without the addition of the adjuvant AgRHO DR-2000ò,are in Table4.

No signi?cant differences were found between the evaporation rates and the densities of the spray liquids for the different formulation types.

Hewitt(1998)states that,with hydraulic nozzles,evaporation rate and density of the spray liquid is of less importance than with rotary and hollow cone nozzles.The evapo-ration rate of hydraulic sprays is generally low,because the droplet size spectrum of hydraulic sprays is medium to coarse,whereas the droplet size spectra of hollow cones are ?ner,and thus the droplets are more prone to evaporation.Although there are indications that adjuvants in commercials pesticide formulations can affect evaporation,they can either enhance or suppress evaporation(Spanoghe2005).From the data in Table4,it can be seen that the addition of AgRHO-2000òhad a small effect on the evaporation rate of the spray liquids.In the cases of Tiltò,Paraatòand Euparen Multiòthere was a small decrease.But,as the?ow time of the spray was only15s in the wind tunnel experiments, this small decrease of v was not expected to have a detectable effect on the drift data,so it was not taken into further account.The addition of AgRHO-2000òto Tiltòand Ronilan Table4Evaporation rates and densities of the spray liquids without and with adjuvant AgRHO DR-2000òadded

Commercial formulation Evaporation rate v(nl s-1)Density q(kg l-1)

Spray liquid Spray liquid?AgRHO

DR-2000ò

Spray liquid Spray liquid?

AgRHO DR-2000ò

Tiltò 1.4±0.012 1.1±0.0120.98±0.00220.98±0.0096 Cytoxò 1.3±0.011–0.99±0.001–

Pyrus400SCò 1.3±0.013– 1.00±0.001–Ronilan SCò 1.0±0.011 1.0±0.013 1.00±0.001 1.00±0.0011 Paraatò 1.2±0.0099 1.1±0.011 1.00±0.000310.99±0.011 Kerb50ò 1.0±0.013–0.99±0.0055–Chorusò 1.2±0.014–0.98±0.0022–Euparen Multiò 1.1±0.012 1.0±0.014 1.00±0.002 1.04±0.034 Caddy100SLò 1.4±0.011–0.98±0.0031–Lannate20SLò 1.0±0.0098– 1.00±0.0011–

SC òhad no signi?cant effect on q .For Euparen Multi òthere was an increase in q of 4%,and for Paraat òthere was a decrease of 1%.Since the changes of the densities were not pronounced,they also were not taken into further account.

The extensional viscosities E (-)of the four spray liquids,upon addition of the adjuvant AgRHO DR-2000ò,were found to be 1.24±0.0007for Tilt ò,1.26±0.0013for Ronilan SC ò,1.25±0.0022for Paraat òand 1.26±0.0019for Euparen Multi ò.The viscosity increase of the spray liquids upon the addition of AgRHO-2000òwas of the same order for all the spray liquids,about 25%in all four.

The results for DST (mN m -1)of the ten spray liquids,with and without the addition of the adjuvant AgRHO DR-2000ò,are in Table 5.

The spray liquids of EC (Tilt òand Cytox ò)and SC (Pyrus 400SC òand Ronilan SC ò)formulations had the lowest values for DST.The DST values for the spray liquids of the WG,WP and SL formulation types varied between 61.8and 70.0mN m -1(Table 5)and these values are close to the value for water (72mN m -1).The DST values of the EC and SC formulation types were considerably lower.Respective DST values of 43.6,36.1,46.4and 44.7mN m -1were found for Tilt ò,Cytox ò,Pyrus SC òand Ronilan SC ò.None of the DST values of the spray liquids were signi?cantly affected upon the addition of AgRHO-2000ò.

Wind tunnel experiments

The drift percentages of the ten spray formulations are given in Table 6.

The correlation coef?cients R 2between the drift percentages of the spray liquids from Table 6and the DST values from Table 5are presented in Table 7.

The correlations between the DST values and the drift percentages were found to be high (R 2=0.80–0.94),except for the distance 2.25m where the R 2coef?cient was 0.68.For the v and q values,poor correlations with the drift data were found (results not presented here).

The DRP upon the addition of adjuvant AgRHO DR–2000òwere 59%for Tilt ò,43%for Ronilan SC ò,75%for Euparen Multi òand 74%for Paraat ò.

Table 5Dynamic surface

tensions of the spray liquids

without and with adjuvant

AgRHO DR-2000òadded Commercial formulation DST (mN m -1)Spray liquid

Spray liquid ?AgRHO DR-2000òTilt ò43.6±1.1943.3±0.46

Cytox ò36.1±0.30–

Pyrus 400SC ò46.4±0.34–

Ronilan SC ò44.7±0.4444.8±0.07

Paraat ò66.8±0.4767.4±0.64

Kerb 50ò69.4±0.73–

Chorus ò61.8±0.49–

Euparen Multi ò70.0±0.4169.2±0.82

Caddy 100SL ò67.3±1.41–

Lannate 20SL ò

69.4±0.41–

T a b l e 6D r i f t p e r c e n t a g e s o

f t h e s p r a y l i q u i d s f o r m u l a t i o n s i

n t h e w i n d t u n n e l e x p e r i m e n t s D i s t a

n c

e (

m

)D r i f t (%)E C l i q u i d S C l

i q u i d W P

l i

q u i

d

W G l i q u i d S L l i q u i d T i

l t

òC y t o x ò

P y r u s

S

C òR o n i l a n S C òP a r a a t ò

K e r b 50ò

C h o r u s òE u p a r e

n M u l

t i

òC a d d y 10

0S L òL a n n a t

e 2

0S L ò0.254.97±0.208.47±0.814.46±0.514.08±0.681.52±0.241.63±0.211.12±0.191.46±0.211.39±

0.421.44±0.290.352.

04±0.143.02±0.382.

11±0.191.

95±0.261.

32±0.231.49±0.161.

09±0.141.34±0.331.25±0.371.31±0.140.500.732±0.0500.783±0.2200.859±0.1690.796±0.1230.984±0.1921.

18±0.130.926±0.1521.10±0.150.998±0.0771.

02±0.110.750.524±0.0180.442±0.1100.401±0.0310.346±0.0800.720±0.1300.743±0.1120.672±0.1200.732±0.0420.706±0.0250.686±0.2061.000.242±0.0580.381±0.0200.329±0.0810.253±0.0220.620±0.1020.6

53±0.1380.590±0.0710.659±0.2080.613±0.0190.629±0.2261.250.128±0.0390.180±0.0060.302±0.0770.238±0.0130.508±0.0860.565±0.1130.489±0.0810.583±0.0210.514±0.1170.573±0.0511.750.

128±0.0190.

120±0.0150.258±0.03460.226±0.0360.471±0.0400.647±0.0200.568±0.0530.474±0.0350.604±0.0300.534±0.0582.250.0830±0.00340.0800±0.00420.192±0.0320.181±0.0290.310±0.0390.376±0.0580.172±0.0350.232±0.0070.252±0.0160.261±0.0773.500.0336±0.00170.0300±0.00740.0467±0.00670.0406±0.00400.152±0.0300.172±0.0320.

119±0.0260.

133±0.0140.136±0.0170.138±0.0444.650.

0174±0.001100.0467±0.006770.0282±0.00665

0.

0172±0.00370.

110±0.0240.

117±0.0210.0798±0.01130.0922±0.00200.0966±0.02020.

103±0.0396.0

0.0

81

2

±

.

19

1

.02

46

±

.

00

56

.

20

1

±

.

00

7

7

.

00

76

8

±

0.0

01

5

80.

7

.

01

5

3

.

9

00

±0

.

01460

.

5

9

8

±

.

00530

.

07

8

±0

.

01

6

70

.

7

80

±

.

008

5

.

06

8

7

±0

.

02

57

Discussion

Viscosity affects droplet formation through resistance to ?ow,which can include elon-gational ?ow if a polymer or other extensional viscosity modifying adjuvant is present in the tank mix.An increase in viscosity tends to cause an increase in droplet size (Hewitt 1998).The addition of AgRHO-2000òto the spray liquids reduced drift most effectively with the spray liquids of Euparen Multi òand Paraat ò,for which DRP values of 75%and 74%respectively were found.AgRHO-2000òappeared to be less effective with the EC-and the SC-like spray liquids Tilt òand Ronilan SC ò,for which respective DRP values of 59%and 43%were found.

As might be expected,the EC and SC spray liquids resulted in most drift near the nozzle and the least drift far from the nozzle (Table 6).The DST value seems to be useful in explaining the drift pro?les:the lower the DST value,the more deposition occurs near the nozzle,and less far from the nozzle.This appears to be in contrast with the literature.Hewitt (1998)states that a lower surface tension causes the formation of ?ner droplets,so short-distance drift deposition decreases while far-distance drift increases.

Two effects may affect atomization:

–Thermodynamic effect.According to the laws of thermodynamics,a system wants to

attain the state with the least free energy.Therefore,the lower the surface tension of a liquid,the more ?ner droplets will be formed instead of one large droplet,to increase the total liquid surface.This is an equilibrium effect,found within reversible systems.–Kinetic effect.When a liquid is pumped through a nozzle under hydraulic pressure,the

liquid comes out of the nozzle as a liquid sheet,which subsequently breaks-up into droplets.A lower surface tension promotes quicker break-up of the liquid sheet at the nozzle tip.This effect is irreversible and causes the formation of coarser droplets.Depending on the spray pressure applied and the nozzle used (i.e.nozzle opening size),one of the two effects will dominate.For example with low spray pressures and coarse nozzles,more of the thermodynamic effect can be expected.Work to con?rm this was done by Spanoghe (2005),who states that the SPAN factor of the droplet size distribution spectrum of the spray liquid/nozzle/pressure combination should be considered.The SPAN factor is the relative amplitude of a droplet size distribution spectrum,and is de?ned as (D v 0.9-D v 0.1)/D v 0.5with D v 0.9the droplet diameter such that 90%of the volume of the sprayed liquid is Table 7Correlations between

the DST values of the spray

liquids and the drift percentages Distance (m)R 20.25

0.860.35

0.800.50

0.820.75

0.841.00

0.851.25

0.941.75

0.882.25

0.683.50

0.944.65

0.826.000.87

constituted of droplets of a smaller size;D v0.5is the droplet diameter such that50%of the volume of the sprayed liquid is constituted of droplets of a smaller size,also known as the Volume Median Diameter(VMD);and D v0.1is the droplet diameter such that10%of the volume of the sprayed liquid is constituted of droplets of a smaller size.Spanoghe deter-mined the droplet size spectra of Euparen Multiòand Ronilan SCòwith a Malvern particle sizer.He found respective data of120,225and405l m for the D v0.1,the VMD and the D v0.5 of Euparen Multiò.For Ronilan SCòSpanoghe found values of95,260and750l m for the D v0.1,the VMD and the D v0.5.

From the droplet size data,SPAN factors of1.27and2.52were calculated for Euparen Multiòand Ronilan SCò,respectively.The spectrum of Ronilan SCòis broader than the spectrum of Euparen Multiòand contains a fraction of very?ne droplets(kinetic effect of the low DST)and a fraction of very coarse droplets(thermodynamic effect of the low DST)compared to the spectrum of Euparen Multiò.It is to be expected that the fraction of coarse droplets of Ronilan SCòwould settle near the nozzle,while the fraction of?ne droplets would be very drift-prone,and this fraction was not detected in the wind tunnel (i.e.drift distance[6m).

Conclusions

Droplet size and drift occurrence is an interaction between spray technique(spray pressure and nozzle selection)and physicochemical properties of the spray liquid.Much research has been done on the in?uence of weather conditions and the spray application technique on drift(Nuyttens2007)but little research has been done on the in?uence of physico-chemical parameters on drift,probably because of the even more complex interactions than between weather conditions and spraying techniques.

Two conclusions can be reached from our work:

–Increasing the viscosity of the spray liquid leads to a decrease in drift occurrence through the formation of coarser droplets.Addition of a drift-reducing polymer,such as AgRHO-2000ò,which consists of polyacrylamide,was found to be less effective with EC and SC spray liquids than with the WG and WP spray liquids.The reason is not known,but there might be a masking effect caused by the low DST values.

–It cannot be stated categorically that a lower surface tension leads to?ner droplets and thus more drift(Hewitt1998)as a lower surface tension can also lead to coarser droplets and thus less drift.

References

ASTM E2408-04.(2006).Standard test method for relative extensional viscosity of agricultural spray tank mixes,4pp.

Brusselman,E.,Nuyttens,D.,Baetens,K.,Gabriels,D.,Cornelis,W.M.,Van Driessen,K.,et al.(2005).

Wind tunnel tests with different tracers and collection techniques for the measurement of spray drift.

Annual Review of Agricultural Engineering,4(1),303–311.

Gabriels,D.,Cornelis,W.,Pollet,I.,Van Coillie,T.,&Quessar,M.(1997).The ICE wind tunnel for wind and water erosion studies.Soil Technology,10(1),1–8.

Henderson,D.C.,&Micale,F.J.(1993).Dynamic surface tension measurement with the drop mass technique.Journal of Colloid and Interface Science,158,289–294.

Hewitt,A.J.(1998).The importance of nozzle selection and droplet size control in spray application.

Proceedings of the North American Conference on Pesticide Spray Drift Management.March29–April 1,(pp.75–85).

Nuyttens,D.(2007).Drift from?eld crop sprayers:The in?uence of spray application technology deter-mined using direct and indirect drift assessment means(PhD Dissertation,Faculty of Bioscience Engineering,Catholic University of Leuven).267pp.

Spanoghe,P.(2005).Effect van additieven en adjuvantia op de ef?cie¨ntie van de spuittoepassing van gewasbeschermingsmiddelen(PhD Dissertation,Faculty of Bioscience Engineering,UGent).301pp. Tomlin,L.D.S.(2006).A world compendium.The Pesticide Manual,(14th ed.,pp.697–698).

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