A comparison of the drift potential of a novel twin fluid nozzle with conventional low volume flat fan nozzles when using a range of adjuvants

Cro,~ Protecrron Vol. IS. No 2. pp 147-152, 1996 Copyright 0 19Y6 Elsewrr Science Ltd Printed in Great Bntain Ail rlghtr reserved wl-2lY4/96 $lS.(Wl + 0.00

0261-2194(95)00089-5

ELSEVIER

A comparison of the drift potential of a novel twin fluid nozzle with conventional low volume flat fan nozzles when using a range of adjuvants J.H. Combellack* *SpraySmart

N.M. Western+

Enterprises,

Ashton

Research

Ashton,

Bristol

27

Station,

and R.G. Richardson*

Bedford

Street,

Department

of

BS18 9AF, UK, and *Department

Turnbull Research Institute,

Box

Hill,

Agricultural

Victoria

3128,

Sciences,

of Conservation

Australia,

University and Natural

of

tlACR-Long Bristol,

Long

Resources,

Keith

Frankston 3199, Australia

Spray drift from a novel twin fluid nozzle and low volume hydraulic pressure flat-fan nozzles has been measured in a wind tunnel. At a wind speed of 4.2 m s-l, drift from the twin fluid nozzle, spraying a range of adjuvants increased with decreasing flow rate. Emulsifiable oil adjuvants produced less drift than an ethoxylated alcohol surfactant, in general agreement with data on in-flight droplet spectra. Comparing drift between the twin fluid nozzle and the flat fan nozzles at a constant flow rate of 600 ml min showed that drift from the former was intermediate between standard and low-drift nozzles. Drift increased with increasing spray release height, but for the twin fluid nozzle at 400 ml min-’ at 50 cm was smaller than that from the same nozzle atomising 150 ml min-’ at a height of 35 cm. Air inclusions in droplets from the twin fluid nozzles did not influence drift. The need for a technique to measure the mass of droplets containing air inclusions is highlighted and the method of plotting drift at variable wind speeds is discussed. Keywords:

nozzles; adjuvants;

spray drifts

Airborne movement of spray droplets containing herbicides onto non-target areas poses an injury or damage threat to biota, environment and or property. There is widespread public disquiet and anxiety about spraying typified by fear of exposure to drift. In view of these concerns it was considered expedient to compare spray droplet drift from a novel low volume (25-50 I ha-‘) twin fluid spraying system with commercial flat fan hydraulic pressure nozzles. The new nozzle was designed to have a large (1.8 mm diameter) orifice to reduce blockages and to be used over a wide (150-600 ml min-‘) range of flow rates, allowing application volume to be maintained over a four-fold speed range. A knowledge of the drift potential from such nozzles, over the envisaged flow rate range, was considered prudent if the system was to be viable. The interactive factors governing droplet drift from hydraulic nozzles have been reviewed (Combellack, 1982; Elliot and Wilson, 1983; Miller, 1993). These reviews defined the critical parameters involved but provided little data on sprayer operating parameters or formulation effects. Critical factors which govern droplet sedimentation are for example, their size and velocity (Elliot and Wilson, 1983) which are influenced by evaporation through formulation and humidity (Miller, 1988; Miller and Hadfield, 1989), and dispersion via air turbulence and wind speed (Elliot and Wilson, 1983; Lawson, 1979; Miller 1993). Sprayer speed and air flow around the boom are also important (Miller et al., 1989; Young, 1990, 1991).

In view of the complexity of such interactions, field studies are typically too variable to permit easy comparisons between interacting effects. Drift estimations using dispersion (Bathe and Sayer, 1975) or random walk (Thompson and Levy, 1983) models have been attempted to overcome these difficulties. The two approaches have given reasonable predictions especially the more recent random walk models that account for sprayer-induced turbulence (e.g. Miller and Hadfield, 1989; Walklate, 1991). Two key inputs into these models are droplet size and velocity. While droplet spectra are reported for another twin fluid nozzle (Cowell and Lavers, 1987; Miller et al., 1990), laser droplet sizers are unable to accurately appraise the droplet sizes from the twin fluid nozzle used in these tests (Miller, pers. commun.). Therefore drift predictions based on droplet spectra were not an option with the twin fluid nozzles being assessed, so measurement of drift was the only rational alternative. Wind tunnels have given comparable droplet drift results to field results (Western et al., 1989) and offer a viable option. A recent study at four United Kingdom research institutes showed that it is possible to obtain reasonably consistent relative drift measurements in different wind tunnels if reference nozzles and standard procedures are adopted (Miller, 1992). It was therefore resolved to compare the relative drift of the twin fluid nozzles with hydraulic flat fans using a wind tunnel. A wheat stubble on the floor of the tunnel was shown to simulate the wind profile over vegetation (Miller,

Crop Protection

1996 Volume 15 Number 2

147

Drift potential

of a novel twin fluid nozzle: J.H. Combellack

et al.

al.,

directed. through a 1.8 mm orifice onto a specially fabricated deflector tip.

Materials

(b) Hydraulic nozzles. Four each of standard (Spraying Systems SF11002VK), extended range (Spraying Systems XR11002VS) and low drift (Sprays International 11002LD) 110” flat fan nozzles were spaced at 50 cm on a wet boom and suspended 35 cm above the stubble. Flow rate, (600 ml min-’ nozzle-’ and delivered at a pressure of 185-195 kPa), was measured with an impeller flow meter (Litre Meter, UK).

1992). As the spectra from both the twin fluid (Miller et 1990) and conventional and low drift flat fan nozzles (Barnett and Matthews, 1992) vary with formulation, a range of adjuvants were included to assess their influence on atomisation and drift. Drift of droplets containing air inclusions was considered especially important thus adjuvants which gave a nil to high incidence of inclusions were tested.

and methods

(i) Wind tunnel (iii) Adjuvants

All the studies were carried out in the Long Ashton Ressearch Station’s wind tunnel which has been described by Hislop (1989). The tunnel floor was covered with a 25 cm wheat stubble in trays for the 5 m distance from the nozzles to the spray collectors to simulate the wind profile over vegetation (Miller, 1992). Wind speed was measured using a three axis ultrasonic anemometer (Gill Instruments Ltd., UK) placed upwind of the boom at nozzle height.

and their physical

description

Details of the adjuvants and concentrations used are presented in Table 1. They were selected to represent those commonly used with herbicides in small grain crops in Australia along with two experimental products which influence the formation of air inclusions in droplets from twin fluid nozzles. Equilibrium surface tensions (EST) were measured with a torsion balance (White Instruments) and dynamic surface tension (DST) using a maximum bubble pressure method at 30 Hz (ICI Surfactants, Australia). The incidence of air inclusions was estimated by collecting the spray from the twin fluid nozzle in a petri dish containing a 5 mm layer of silicon fluid (6509 200/1000 cs, Dow Corning, USA) topped by 8-10 mm of oil (Shellsol T, Shell, Australia). The droplets were inspected using a binocular microscope (Olympus, Model LGPS, Japan) illuminated with cold light source (Fibre Optics Ring Light, Olympus, Japan). The assessments are presented in Table 1.

(ii) Spray boom and nozzles (a) Twin fluid nozzles. A boom with four twin fluid nozzles spaced 50 cm apart was suspended either 35 or 50 cm above the stubble. Air pressure and flow from a compressor were regulated by a O-4 bar constant flow regulator (Norgren, UK), flow was measured by a 10-100 1 min-’ variable area flow meter (Platon, UK) and pressure by a O-100 kPa pressure gauge (Dobbie Instruments, Australia). Air was delivered to individual nozzles by tapping a 6 mm male stud run tee (Legris International) into a 25 mm plastic airline. A 12V DC gear pump (Micropump, USA, model 120-000) was used to deliver the liquid to the nozzles. Flow rate changes were effected by varying voltage to the pump. The liquid was fed from the pump into a 12.5 mm plastic tube and then to individual nozzles via a 40 cm length of 4 mm o.dY1.8 mm i.d. nylon tube push fitted into a 6-4 mm reducer in the male stud tee. Liquid flow was measured with a 200-3000 ml min-’ variable area flow meter (Platon, UK) and pressure with a O-150 kPa gauge (Dobbie Instruments, Australia). The air/liquid mix within the body of the male stud run tee were then

(iv) Spray drift measurement

Droplet drift was measured using cotton collectors and fluorescent tracers as described by Western et al. (1989). White mercer 20 gauge crochet cotton (Twilleys for 50 cm and Coats for 35 cm boom heights) with a diameter approximately 0.5 mm was used as the collector. The 11 collectors, 2.9 m long, were placed horizontally across the tunnel at 10 cm intervals from the top of the stubble to 1.0 meters above. For all tests the spray liquid contained 0.05% sodium fluorescein (British Drug House, Product 2849) in tap water plus

Table 1. Adjuvant details

BSlOOO KTRI I KTRI 9 D-C-Trate *Equilibrium ‘Dynamic *Level

surface surface

(450

BSIOOO KTRI

0.1 0.5 0.5 0.2 tension-means

tension-means

of air inclusions

or high I

ml mine’

9

(150

and 15 I min-’

ml min.’

air)

flow

85%

refined

canola

oil plus 15%

canola

oil plus 15%

double

85% 260%

double

48.8 62.6 63.2 62.2

H L-M L-M nil

H M-H L-M nil

liquid

and 20

I min-’

air)

rates

of a synthetic

alcohol

manufactured

of a five ethylene

for ICI

oxide

Cropcare

alkylphenol

Australia,

ethoxylate

1 Nicholson

formulated

St. Melbourne,

by Keith

Turnbull

Australia

Research

Institute,

PO

Box

48,

Australia refined

Turnbull light

33.0 31.0 28.5 38.5

cm-‘)

replicates

derivative

Petroleum,

148

at low

Air inclusions Low$ High$

DST+ (dynes

replicates

oxide

Keith D-C-Trate

measured liquid

of three of three

polyalkylene Frankston,

KTRI

EST* (dynes cm-‘)

Concentration (% v/v)

Adjuvant

Research

solvent

dewaxed

499 St Kilda

Crop Protection

Institute, Rd.

PO

paraffinic Melbourne,

of a five and nine ethylene Box 48, Frankston, oil plus <20% Australia

1996 Volume 15 Number 2

oxide

alkylphenol

ethoxylate

and sodium

dodecyl

benzene

sulphonate

water

manufactured

formulated

Australia

mixture

of polyglycol

and sorbitan

fatty

acid esters and
by Ampol

by

Drift potential of a novel twin fluid nozzle: J.H. Combellack et a/.

an adjuvant as detailed procedure was used:

in

Table 2. The

following

a. the nozzles were adjusted to the correct liquid and/or air flow rates and then turned off; b. the sampling lines were erected; C. the fan was turned on and the wind speed was adjusted to the desired level; d. the spray was turned on for the prescribed interval, 30 seconds for the twin fluid and 20 seconds for the hyraulic fan nozzle; e. the spray was turned off; f. the fan was turned off; g. the sampling lines were removed and immediately placed in glass jars containing 20 ml of an fluid comprising 0.05M sodium extraction hydroxide and 0.05% of Triton Xl00 nonionic wetting agent (Union Carbide) in distilled water; h. the extracted tracer was then measured in a spectrofluorimeter (Perkin Elmer LS2) using an excitation wavelength of 450 nm and an emission wavelength of 510 nm; in spray volumes, i. to account for differences spraying time, spray concentration and wind speed the amount of tracer collected per string was normalised as ng mm-’ g-’ of tracer released.

(v) Droplet spectra

measurements

Droplet spectra for the flat fan hydraulic nozzles were measured using a phase doppler analyzer (Aerometrics, USA). Liquid pressure was adjusted using a constant flow regulator (Norgren, UK) and flow rate measured with an impeller flow meter (Litre Meter, UK). A representative sample was obtained by taking a single scan through the long axis of the spray cloud 10 cm below the nozzle tip. The data are presented as Table 3.

Results Influence of flow rate, boom height and formulation on drift from twin fluid nozzles Figure I shows that as the liquid flow rate increased from 150 to 600 ml min-’ so drift decreased as did the differences between the adjuvants. The emulsified canola oils (KTRI 7 and 9) produced significantly less drift (P = 0.05) than both the alcohol ethoxylate (BSlOOO) and emulsified petroleum oil (D-C-Trate) at both boom heights at a liquid flow of 150 ml min-’ (Table 2). There were no significant differences at the other flow rates tested. These results suggest that air inclusions which were noted in droplets of 13&150 pm and greater (high for BSlOOO, medium for KTRI 9 and nil for D-C-Trate) have little or no influence on droplet drift. The data were fitted to a range of regression equations to explain the curves. Two equations - one based on a power and the other an exponential function, gave good fits. Of the two the exponential function was considered the better as when regressed to the x axis the estimate was closer to the theoretical maximum (9-10,000 ng mm-’ g-l). The data were thus fitted to the equation:

Spray collected = a*EXP(b*FLOW).

Using this equation the corrected coefficient of correlation ? ranged from 0.970 to 0.996. Thus the equation can be used to confidently predict drift over the range of flow rates and for the two boom heights tested. Raising the boom height from 35 to 50 cm resulted in an overall 72% significant (P = 0.05) increase in drift (Table 2). This difference was reasonably consistent over the flow rates tested (150-600 ml min-‘). Drift from twin fluid nozzles atomising solutions containing KTRl 7 (0.5%) and D-C-Trate (2.0%) at a flow rate of 150 ml min-’ with the nozzles set 35 cm above the stubble and 400 ml min-’ when 50 cm above measured using wind spreeds of l-4.2 m set-’ (Figure 2) showed only a small variable difference between the two formulations. Subjecting data for the 35 cm boom height and 150 ml min- flow rate to a simple linear equation produced ? values of 0.97 and 0.99 for KTRI 7 and D-C-Trate respectively. The data is better described by a sigmoidal curve as it can be assumed that there will be zero drift at zero wind speed+ and a maximum amount of drift that does not increase with increasing wind speeds. When fitted to the function: DRIFT (ng mm-’ g-’ tracer emitted)

=

a-a/(1 + exp(-2* (b + c*WTND))),

Table 2. Effect of boom height and adjuvant on drift (ng mm-’ g-‘) from twin fluid nozzles operating at 150 ml min-’ flow rate in a 4.2 m s-’ wind Adjuvant

Concentration (% v/v)

BSlCiN D-C-Trate KTRI 7 KTRI 9 Column mean

0.1 2.0 0.5 0.5

Means followed columns,

by the same letter

upper

case column

= (1.05) using Tukey’s

3380.7;’ 3304.7” 2772Sh 2541 .4h

5834.2” 571 1..Y 4628.5h 4302, I ”

2999.4”

5166.P

(lower

and row

pairwise

Row mean

Boom height 35 cm 50 cm

case for boom

means)

comparison

heights

are not significantly

4607” 45oP 3701 R 3517”

within different

(P

test

600000

-,

400000

2 E 2 E b

300000

200000

1 I’00 to:>

0.00 010

021

032 043 Llq"ld"ow rate((th")

054

065

Figure 1. Effect of liquid flow rate and formulations on drift production from twin fluid nozzles operating at 35 and 50 cm above the target surface

+It can be argued that at some wind speed above zero there will be zero drift caught at 5 m down wind. However. as the lowest wind speed used was 1 m s-’ It was considered imprudent to extrapolate the model to meet this requirement.

Crop Protection

1996 Volume

15 Number

2

149

Drift potential of a novel twin fluid nozzle: J.H. Combellack et al. The effect of formulation hydraulic nozzles

0

1

2

3

4

Drift from flat fan and twin fluid atomisers, operated at 600 ml min-’ nozzle-‘, in a 4.2 m set-’ wind, 35 cm above the stubble are presented in Table 4. The type of hydraulic nozzle and the adjuvant used significantly affect drift. The low drift nozzle created significantly (P = 0.05) less drift than the other nozzles. Compared with the low drift the mean increase in drift was 262% for the extended range, 221% for the standard fan and 161% for the twin fluid. The twin fluid nozzle significantly (P = 0.05) reduced drift compared with the extended range (38%) and the standard fan (27%). Of the formulations using KTRI 9 created significantly (P = 0.05) less drift than D-C-Trate with BSlOOO giving by far the most drift. The most drift was created with the extended range nozzle spraying BSlOOOwhich gave 590% more drift than the least drift prone combination of low drift nozzle with D-C-Trate. The twin fluid nozzle, unlike the hydraulic flat fans, created similar drift with each of the adjuvants.

5

Wind speed (mlsec)

Figure 2. Effect of wind speed on drift from twin fluid nozzles operating at 150 ml min-’ at 35 cm boom height and 400 ml min-’ at 50 cm boom height

the 12 values for D-C-Trate and KTRI 7 were >0.99. The curve fit and extrapolations are better when this model is used. The data for the 50 cm boom height at 400 ml min-’ per nozzle liquid flow also fit better using this equation (? = >0.99 for both D-C-Trate and KTRI 7). Also a lower flow rate (150 compared with 400 ml min-‘) exacerbates drift more than a raising of the boom height from 35 to 50 cm.

Discussion

The basis of predicting spray droplet drift is understanding the interaction between the motion of the droplets and the air into which they are released, one therefore needs to have knowledge of droplet mass and calculate, or measure, their emission velocity from the nozzle. Since droplets produced by twin fluid nozzles can have air inclusions, their velocity must be measured as they decelerate to their terminal velocity faster than ‘solid’ droplets due to their lower mass (Miller et al., 1990). Such information would enable a calculation of the settling time from a given release height. Such theoretical predictions appeal since droplet spectra measurements are relatively quick and cheap compared to drift measurements. To measure droplet size and velocity ‘in-flight’, two phase Doppler systems (Aerometrics and Dantec) and an optical shadowing system (Particle Measuring System) were used. Both phase Doppler systems gave very low validation figures and hence unreliable data, with twin fluid nozzles. This reflects the difficulty of measuring droplets with air inclusions even when the forward light scattering mode was used (Young, pers. commun .) . Air inclusions should not be the only problem as some of the solutions used produced sprays with no air inclusions. Attempts to overcome the problem with the Aerometrics, including adjustments to both the

Droplet spectra from flat fan nozzles

The low drift nozzle had a higher VMD, except for BSlOOO and lower small droplet component compared with the extended range and standard flat fans. However, smaller VMDs and increased volumes of small droplets from the extended range compared with standard nozzles, with three out of the four adjuvants, was less predictable as it is generally thought that the extended range nozzles produce less small droplets than standard flat fans. The variation in the ‘optimal’ droplet size range was considerable, ranging from a high of over 60% to a low of 33% of the volume. These data clearly show that subtle changes in formulation together with nozzle type have a significant effect on the volume of spray in such droplet classes. For example, KTRI 7 and 9 produced a similar volume of these droplets with the extended range and standard nozzles, but with the low drift nozzle KTRI 7 produced significantly more than KTRI 9. BSlOOO produced a minimum of 2.5 times the volume of small droplets (
on the droplet spectra from selected flat fan hydraulic

Nozzle 11002XR 11002SF 11002LD

A 273 252 265

B 5.6 5.6 5.3

C 55.0 61.4 56.5

A 300 308 325

B 3.0 1.6 1.6

A = Volume Median Diameter B = % volume in droplets of
150

nozzles at a flow rate of 600 ml min-’ KTRI 7 (0.5%)

D-C-Trate (2.0%)

BSlOOO (0.1%)

Crop Protection 1996 Volume 15 Number 2

on drift from a range of

C 48.7 47.4 39.9

Systems,

A 289 299 304

Wheaton,

B 2.5 1.8 2.1

Illinois,

USA,

KTRI 9 (0.5%) C 51.0 48.1 46.4

A 296 308 348

B 2.4 1.4 1.2

11002LD ex Sprays International,

C 51.0 46.1 33.2

35 Paul Street

Drift potential Table 4. Drift from fiat fan and twin fluid nozzles, wind Flow (ml min-‘)

Nozzle

Means

followed pairwise

Drift BSIOOO

by the same letter comparison

(lower

case for adjuvant

types

within

when operating

D-C-Trate

5fWh 609” 317’ 553” 511C columns.

upper

case column

et al.

at a boom height of 35 cm and in a 4.2 m-’

(ng mm-’ g-’ tracer emitted) KTRI 9

1621” 1334h 562” 694’ 1053A

600 600 600 600

11002XR llOO2SF I 1002LD Twin-fluid Column mean

Tukey’a

using three adjuvants,

of a novel twin fluid nozzle: J.H. Combellack

Row mean I OOYA 853’3 385” 622[

840” 61P 275’ 620h 587’ and row means)

are not significantly

different

(P = 0.05)

using

test

droplet size range and the diffraction constant were unsuccessful. Attempts to measure the droplet spectra using the PMS also failed, despite success with another twin fluid nozzle (Miller et al., 1990). This was possibly due, in part, to the maximum droplet size that could be measured, around 650 pm, being too small (Miller pers. comm.). though the data were not sufficiently skewed toward the large droplet component for this to be the sole explanation. As data have been reported for another twin fluid nozzle with one of the systems used (a Dantec system, Miller, 1992), this makes the reasons for these results all the more perplexing. Further, while a number of droplets have been observed over 800 pm when captured in oil/silicone layers they do not account for a large proportion by number. It is recognised that the latter technique is also an inaccurate appraisal of spectra as large droplets often shatter when they impact on the oil surface and they may be even more prone to this if they contain air inclusions. The failure to measure the droplets size and velocity acurately from the twin fluid nozzles meant that it was impossible to develop a drift mode1 based on these parameters. These experiments demonstrate the need for a method to measure the spectra from such nozzles. The Long Ashton Research Station wind tunnel provided a reliable and reproducible means of measuring spray drift, especially as a stubble reduced turbulence (Hislop pers. commun., Miller, 1992). Drift was measured at five rather than two metres downwind as suggested by Miller (1993) as this was considered more applicable to field practice. Increasing the downwind distance also reduces the volume of drift collected and permits longer sampling times, around 30 s in these tests compared with 10-15 s if sampled at two metres, thus reducing the error in cut off times. Drift measurements with the twin fluid nozzle in a 4.2 m s-’ wind show that an increase in boom height of 15 cm results in an overall 72% increase in drift (Table 2). This supports field studies by Nordby and Skuterud (1975), Bode, Butler and Goering (1976) and wind tunnel measurements (Miller, 1992) that boom height has a dramatic influence on drift. The adverse influence of boom height on drift can be overcome by increasing the flow rate from 150 ml min-’ to 400 ml min-’ (Figure 2). Indeed, considering Figures I and 2 it is seen that increased liquid flow rate decreases drift. Consequently, if these twin fluid nozzles are used to accommodate a range of sprayer speeds, by increasing liquid flow rate proportionately to ground speed, drift would decrease as speed increased. In these tests 30.7% of the spray volume drifted at a flow rate of 150 ml min-‘, reducing to 6.2% at 600 ml min-’ (Tables 2 and 4).

These studies showed that air inclusions in the droplets had a minimal effect on drift. BSlOOO produced a large proportion of droplets with air inclusions (Tuble I) and, at 150 ml min-’ , the highest level of drift (Figure 2). Although, at the same flow rate, D-C-Trate induced virtually no air inclusions and KTRI 7 and 9 low to medium numbers, D-C-Trate produced significantly more drift than the latter two adjuvants. At 400 ml min-’ flow rate there were no significant differences in drift between KTRI 7 and D-C-Trate (Table 2). The tendency for an adjuvant to form air inclusions could well be mostly related to dynamic surface tension. For BSlOOO it is very low and lower for the two KTRI adjuvants than for D-C-Trate (Table I). Drift from the twin fluid nozzles increased with increasing wind speed. While many authors have used a linear equation to fit the curves produced (Gilbert and Bell, 1988; Western et al., 1989; Miller et al., 1990; Miller, 1992; Maybank et al., 1978), these data like others (e.g. Gilbert and Bell, 1988) suggest that a linear relationship is not sufficiently sensitive for low (>l m s-‘) nor high (~8 m s-‘) wind speeds. An exponential equation fitted better and it is postulated that it would predict drift more accurately at lower and higher wind speeds. Further, from an inspection of the curves in data reported by Miller et al. (1990) and Miller (1992), an exponential model would possibly provide a better fit for many of their data sets. The droplet spectra data (Table 3) shows that BSlOOO produced the largest volume in droplets of less than 100 km diameter. The large volume of droplets
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1996 Volume

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Drift potential of a novel twin fluid nozzle: J.H. Combellack et a/. between the two sets of data is not possible as the measuring systems were different. Nevertheless, both sets of results clearly illustrate the need for caution when recommending changes in nozzle/adjuvant combinations. With the flat fan nozzles, BSlOOO produced significantly more drift than any other adjuvant and overall KTRI 9 the least. From the data there was approximately an 80% reduction in drift from the most drift prone nozzle adjuvant combination, BSlOOO sprayed through an extended range nozzle which gave 16.2% drift, to the least, KTRI 9 or D-C-Trate (5.5-6.2%) through a low drift nozzle. The use of a low drift nozzle with either of the latter two adjuvants therefore offers a simple way to minimise drift. A comparison of the drift from a twin fluid nozzle at the same flow rate (600 ml min-‘) shows that they create significantly less drift than the standard and extended range flat fans, which confirms the findings of Miller et al. (1990) and Miller (1992). However the low drift nozzles created significantly less drift at the same flow rate as the twin fluid nozzles. These studies confirmed that the treatments which created large volumes of small droplets generally gave the most drift. From the droplet spectra data generated it can be calculated that the maximum driftable droplet size for the flat fan nozzles was 115-150 urn rather than the commonly adopted figure of 100 urn and supports the findings of Miller et al. (1990). It would therefore seem prudent to consider droplets of <150 urn as being drift prone, though the figure of 100 urn remains a reasonable approximation. An examination of the physical characteristics of the sprays (Table I) shows that BSlOOO, with its low dynamic surface tension consistently gave higher volumes of small droplets and hence the most drift. The canola oil adjuvants tested had high dynamic surface tension even though their equilibrium surface tension was relatively low (<31 dynes cm-*). From observations, D-C-Trate produces an emulsion while the KTRI 7 and 9 formulations give dispersions i.e. they phase separate within hours. The droplet spectra and drift data therefore suggest that dispersions produce more ‘optimal’ droplets, though both the emulsion and dispersions reduced drift compared with BSlOOO. The internal characteristics of the twin fluid nozzle produce greater shear forces than the hydraulic nozzles, particularly at low liquid flow rates, and under these conditions the D-C-Trate emulsion produced more small droplets than the KTRI 7 and 9 dispersions. This suggests that formulation changes can be reflected as significant differences in the droplet spectra from high shear nozzles.

The senior author thanks the Grains Research and Development Organisation for awarding a Senior Research Fellowship to undertake these studies. Also the guidance of Dr Eric Hislop, LARS, Dr Paul Miller, Silsoe Research Institute and the assistance Pamela Herrington were greatly appreciated.

Crop Protection

Bathe, D. A model

H. and Sayer, W. J. D. (1975) Transport of aerial spray. of aerial dispersion. Agric. Meteorol. 15, 257-271.

I.

Barnett, G. S. and Matthews, G. A. (1992) Effect of different fan nozzles and spray liquids on droplet spectra with special reference to drift control. Inf. Pest Control 34(3), 81-83 Bode, L. E., Butler, B. J. and Goering, C. E. (1976) Spray drift and recovery as affected by spray thickener, nozzle type and nozzle pressure. Transactions Am. Sot. Agric. Eng. 19, 213-218 Cowell, C. and Lavers, A. (1987) A laboratory examination prototype twin-fluid nozzles. Aspects Appl. Biol. 14, 35-52

of two

Elliott, J. G. and Wilson, B. J. (1983) The influence of weather on the efficiency and safety of pesticide application. BCPC Occasional Publication No. 3 Gilbert, A. J. and Bell, G. J. (1988) arising from pesticide spray application. 375

Evaluation of drift hazards Aspects Appl. Biol. 17, 363-

Mayhank, J., Yoshida, K. and Grover, R. (1978) Spray drift from agricultural pesticide applications. J. Air Pollut. Control Assoc. 28, 1009-1014 Miller, P. C. H. (1993) Spray drift and its measurement. In Application Technology for Crop Protection, Eds. G.A. Matthews and E.C. Hislop Miller, P. C. H. (1988) Engineering Aspects of Appl. Biol. 17, 377-384

aspects

of spray

drift control.

Miller, P. C. H. and Hadfield, D. J. (1989) A simulation of the spray drift from hydraulic nozzles. J. Agric. Eng. Res. 42, 135-147 Miller, P. C. H., Mawer, C. J. and Merritt, C. R. (1989) tunnel studies of the spray drift from two types of agricultural nozzle. Aspects Appl. Biol. 21, 237-238

Wind spray

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1996 Volume 15 Number 2

Young, B. W. (1991) A method for assessing the drift potential of hydraulic nozzle spray clouds and the effect of air assistance. Airassisted spraying in crop protection, British Crop Protection Monograph No. 46, pp. 77-86 Received Accepted

6 March 1995 2 June 1995