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MINISTRY OF AGRICULTURE, FISHERIES AND FOOD CSG 15Research and Development

Final Project Report(Not to be used for LINK projects)

Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports UnitMAFF, Area 6/011A Page Street, London SW1P 4PQ

An electronic version should be e-mailed to [email protected]

Project title The effect of formulation and adjuvant use on pesticide spray behaviour

MAFF project code PA1726

Contractor organisation and location

Silsoe Research InstituteWrest ParkSilsoeBeds MK45 4HS

Total MAFF project costs £ 217,661

Project start date 01/04/00 Project end date 31/03/02

Executive summary (maximum 2 sides A4)

BackgroundThe importance of the physical properties of the spray liquid in influencing the droplet size and velocity distributions produced by different designs of agricultural spray nozzle is now well recognised. While some correlation between dynamic surface tension and spray droplet size has been established, there is now strong evidence to suggest that there are other factors influencing the spray formation process with a given nozzle design. The ability to predict droplet size distributions from a nozzle design spraying a liquid having measured physical characteristics has important implications for spray performance and risk assessment procedures. A multivariate regression analysis relating the physical properties of the spray liquid to droplet size characteristics was undertaken by the US Spray Drift Task Force and results from the analysis were used in the initial modelling approaches developed by the Task Force to predict spray behaviour. Comparisons of the predictions made with the Spray Drift Task Force model and results obtained from MAFF – funded studies at Silsoe Research Institute showed relatively poor agreement and one of the factors contributing to this may have been the air flow conditions in the region of spray formation when measurements were made. It is known that changes in air velocity influence spray formation processes and the purpose of this study was to determine the relative magnitude of any such effects for nozzles operating on a typical boom sprayer.

While many studies have quantified the effects that spray liquid properties can have on droplet size distributions, only a relatively small number of authors have reported direct measurements of the implications for spray drift. It is known that, for a given nozzle design, the risk of drift can be related to the percentage of spray volume in small droplets (e.g.<100 m). However, drift is a function of droplet velocity (speed and direction), entrained air conditions and spray structure. Downwind spray drift profiles associated with different nozzle types and examples of different liquid properties have been measured so as to directly assess the implications that changes in liquid properties can have for drift. Such information is relevant to risk assessment procedures and could have implications for buffer zone schemes such as the LERAP system operating in the UK.

Physical properties of the spray liquid are also important factors influencing spray retention and coverage. Many of the experiments conducted to date have used single pot-grown plant targets treated with a flat fan nozzle giving a uniform volume distribution pattern across the sprayed swath from a single nozzle. While this has provided useful data on which

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Projecttitle

The effect of formulation and adjuvant use on pesticide spray behaviour

MAFFproject code

PA1726

to base model predictions, it is important to establish whether the same trends are obtained using a wider and more typical range of nozzle designs to treat realistic cereal crop canopies. It is recognised that the structure of the leaf surface also has a major influence on spray retention characteristics but this work was concerned only with cereal crop canopies.

Major resultsMeasurement of the characteristics of sprays in low velocity (2 – 8 m s-1) air flows was complex due to sampling biases of droplet sizing instruments. However, evidence suggests that the changes in spray formation mechanisms, and the consequent changes in droplet size distributions, that occur because of changes in spray liquid properties are not affected by these air flows with conventional flat fan nozzles. Because of the difficulty in obtaining reliable samples with complex droplets, the effect of air flows on sprays produced by air-induction nozzles could not be evaluated. However, it is likely that similar results would have been obtained since the mechanisms of spray formation are similar to conventional flat fan nozzles.

It can be concluded, therefore, that measurements made of spray characteristics in still air with a slowly-moving nozzle will be comparable with the characteristics of sprays produced by a moving boom on a ground sprayer in the field.

The physical properties of the spray liquid have been shown to significantly influence both horizontal and vertical drift profiles measured in a wind tunnel, with increases in total airborne spray of up to 150%, compared with water alone, being measured. Although a limited number of spray liquids were tested, it is suggested that spray liquids that are emulsions are likely to reduce measures of spray drift, particularly with low drift and air induction nozzles, although this effect will be reduced if there is a significant level of surfactants present. Water-soluble formulations potentially increase drift if surfactants are present, but the degree to which this occurs depends upon nozzle design and wind speed. The correlation between percentage spray volume contained in droplets smaller than 100 m and spray drift was not good, particularly for the flat fan and hollow cone nozzles, suggesting that estimates of drift potential for different spray liquids based solely on droplet size distributions would not be accurate. Since it has been shown that the droplet size distributions produced by nozzles in wind speeds typically used for drift assessments are similar to those measured during droplet sizing in still air, it is concluded that other factors, including droplet velocities and spray structure, are important in determining drift.

The effect of spray liquid on drift depends upon nozzle design and cannot be predicted without a better understanding of the basic mechanisms. However, when making environmental risk assessments, the importance of including some information relating to spray liquid properties is crucial since the measures of drift can be increased to 270% or reduced to as low as 17% of the levels obtained when spraying with water alone.

Although some studies have shown that spray liquid has a strong influence on the quantity of spray deposited on the target plant, a much smaller effect was observed when simulating field conditions by using a canopy of outdoor-grown plants rather than individual indoor-grown pot plants. Liquid properties are most significant when retention is strongly related to the probability of a droplet being captured on first impact, and re-distribution does not occur. The effect of canopy density and plant structure will be one of the most important parameters to consider when attempting to predict distribution of spray deposits.

Air-induction nozzles gave lower levels of retention than flat fan nozzles, although this difference was largest for high dynamic surface tension liquids. This suggests that their retention could be improved by using lower dynamic surface tension liquids. The effect of nozzle type was of similar magnitude to the effect of spray liquid.

The properties of the of spray liquid, formulations and adjuvants, are important components of the spray application process. Reducing the surface tension through the additions of surfactants is likely to have a significant effect on spray drift and patterns of deposition on the crop, while having only a limited effect on the quantity deposited on target plants, particularly when the crop has formed a canopy. The use of products that form emulsions, which are common pesticide formulations, contributes to maintaining low levels of drift and potentially results in more uniform deposition patterns across a field. It must be recognised, however, that the efficacy of a product also depends strongly on spray liquid properties, and this has not been considered as part of this project.

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Projecttitle


MAFFproject code

PA1726

Scientific report (maximum 20 sides A4)Introduction

A number of studies, and particularly those funded by MAFF in the past decade, have shown the importance of the physical properties of the spray liquid in influencing the droplet size and velocity distributions produced by different designs of agricultural spray nozzle. Changes in the physical characteristics of sprays with liquids representative of realistic spray tank mixes have been shown to be equivalent to a change in spray quality classification (Miller and Butler Ellis, 2000). The changes measured have been shown to be a function of nozzle type and are influenced by the mechanisms of spray formulation. However, an analysis of a large data set for a range of different types of hydraulic pressure nozzle has shown that sprays formed from liquids based on emulsions generally have a larger droplet size distribution compared with sprays formed from surfactant solutions. While some correlation between dynamic surface tension and spray droplet size has been established, there is now strong evidence to suggest that there are other factors influencing the spray formation process with a given nozzle design. The ability to predict droplet size distributions from a nozzle design spraying a liquid having measured physical characteristics has important implications for spray performance and risk assessment procedures. Work by Hermansky and Krause (1995) used a multivariate regression analysis to fit coefficients to an equation relating the physical properties of the spray liquid to droplet size characteristics measured for the US Spray Drift Task Force. Droplet size distributions were measured with nozzles mounted in a high speed air stream (40-120 mile/h) and results from the analysis were used in the initial modelling approaches developed by the Task Force to predict spray behaviour. Comparisons of the predictions made with the Spray Drift Task Force model and results obtained from MAFF – funded studies at Silsoe Research Institute (Butler Ellis, 1999) showed relatively poor agreement and one of the factors contributing to this lack of agreement may have been the air flow conditions in the region of spray formation when measurements were made. It is known that changes in air velocity around spray generation systems do influence spray formation processes and the purpose of this work was to determine the relative magnitude of any such effects for nozzles operating on a typical boom sprayer. Results from the measurements of spray characteristics in an air flow are therefore relevant to the interpretation of existing droplet size distribution data collected in both nominally still air and high speed air flow conditions and to performance and risk assessment procedures relating to pesticide sprays.

While many studies have quantified the effects that spray liquid properties can have on droplet size distributions, only a relatively small number of authors have reported direct measurements of the implications for spray drift (Western et al, 1999; Butler Ellis et al, 1998). It is known that, for a given nozzle design, the risk of drift can be related to the percentage of spray volume in small droplets (e.g.<100 m). However, drift is a function of droplet velocity (speed and direction), entrained air conditions and spray structure (Miller, 1993). Downwind spray drift profiles associated with different nozzle types and examples of different liquid properties have been measured so as to directly assess the implications that changes in liquid properties can have for drift. Such information is relevant to risk assessment procedures and could have implications for buffer zone schemes such as the LERAP system operating in the UK.

Physical properties of the spray liquid are also important factors influencing spray retention and coverage (Holloway et al, 2000). Many of the experiments conducted to date have used single pot-grown plant targets treated with a flat fan nozzle giving a uniform volume distribution pattern across the sprayed swath from a single nozzle. While this has provided useful data on which to base model predictions, there is a need to demonstrate that the same trends are obtained using a wider and more typical range of nozzle designs to treat realistic cereal crop canopies. It is recognised that the structure of the leaf surface also has a major influence on spray retention characteristics but this work was concerned only with cereal crop canopies.

Recent studies as part of a LINK project and associated commercial measurements have shown that the performance of different designs of nominally the same air induction nozzle give a very different performance. The ability of such nozzles to control drift has resulted in their widespread use but evidence to date, particularly from the MAFF-funded LINK and spray classification projects (Butler Ellis and Tuck, 2000) shows that the performance characteristics of this nozzle design are also very different to those of conventional hydraulic pressure nozzles. The air included nozzle design has therefore been included in the project because of its increasing use in controlling spray drift and because its performance characteristics are very likely to differ from those of conventional nozzles.

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Projecttitle


MAFFproject code

PA1726

1. Investigation of the effect of spray liquid on spray characteristics in an air flow

1.1 Introduction

Extensive measurements have been made to determine the characteristics of sprays produced by agricultural nozzles used in pesticide application, and how they are influenced by spray liquid. Many of these have been conducted in still air, with a stationary or slow-moving nozzle (e.g. Adams et al, 1990, Chapple et al, 1993, Holloway, 1994, Butler Ellis et al, 1999, Butler Ellis and Tuck, 1999). Other work has used wind tunnels or fans to generate high-speed air flows, comparable with relative air speeds associated with aerial spraying (Bouse et al, 1990, Hermanski and Krause, 1995; Hewitt et al, 1994).

Ground spraying operations have a forward speed that averages perhaps around 3 m s -1 in Europe, although there is a trend towards higher speeds. This is relatively low compared with aerial spraying (40 – 60 m s -1) and compared with the speed of the liquid exiting the nozzle (around 10 – 20 m s-1).

It has previously been found that, in still air, emulsion-forming formulations are likely to increase droplet sizes particularly with conventional flat fan nozzles, whereas water-soluble formulations containing surfactants are likely to reduce droplet sizes (Butler Ellis and Tuck, 1999). These effects were as a result of changes in the spray formation mechanism. Measurements in high speed air flows have indicated that an increase in droplet size does not occur with emulsions (Sanderson et al, 1997) and models developed from large data sets do not include such a possibility (Hermansky and Rause, 1995, Teske and Thistle, 2000), suggesting that at high air speeds different mechanisms are dominating. This raises the question of whether, at speeds appropriate to ground spraying, some of the effects seen when spraying in still air conditions may be masked when more realistic conditions apply. However, because of the relatively low air speeds involved, it is hypothesised that the same mechanisms will occur, although the degree of effect they have on droplet sizes may be modified.

The work reported in this paper was therefore undertaken to assess whether a moving air stream, with velocities comparable with the forward speed of a sprayer, affects the droplet size distribution of sprays produced by agricultural nozzles. Measurements were made to evaluate the effect of wind speeds between 2 and 8 m s -1 in a wind tunnel on spray generation and the resulting droplet size distribution. Sampling techniques were devised in order to ensure that the full spray plume was sampled representatively, and the effect of two liquids and different nozzle operating pressures was investigated. High speed photography was used to observe the spray formation process at a range of wind speeds.

1.2 Materials and Methods

A recirculating wind tunnel with a working section 3.0 m wide, 2.0 m high and 7.0 m long was used to generate air speeds between 2.0 and 8.0 m s-1. For the high-speed photography, it was important to ensure that (a) the camera did not block the air flow immediately upstream of the nozzle and (b) the spark flash unit was not wetted by the drifting spray. The nozzle, flash and camera were therefore angled slightly with respect to the wind direction. The flash light source, of 1 s duration, was provided by a PalFlash 500 (Pulse Photonics Ltd) with the slit removed and a diffuser added. The flash and a condenser lens were placed downwind of the spray, with a Hasselblad camera with bellows attachment and 150 mm lens placed upwind.

Two techniques were available for the measurement of airborne droplets: 1-dimensional phase Doppler analysis (Dantec Ltd, Bristol, UK) and a camera imaging system (VisiSizer, Oxford Lasers Ltd, Oxford, UK). The use of phase Doppler analysis (PDA) in the measurement of agricultural sprays is well established and its limitations, in terms of estimating fluxes and measuring droplets with internal interfaces have been documented (Durst et al, 1994, Tuck et al, 1997). Phase Doppler analysis results in a temporal sample, directly related to flux. More recent developments in imaging techniques have led to the use of instruments such as the VisiSizer, which measures particle size and velocity distributions using a technique called particle/droplet image analysis (PDIA) (Murphy et al, 2001). PDIA obtains spatial samples, although since measurement of droplet velocity is also possible, fluxes and the equivalent temporal sample can be calculated.

Instruments used for measurements of droplet size distributions have small sample volumes, and therefore, when measurements are made in still air, this requires moving the spray nozzle in a two-dimensional pattern to ensure that the entire spray footprint is sampled. In the wind tunnel, a one-dimensional transporter was available to move the nozzle across its width. The droplet-sizing instrument therefore needed to be moved in the second dimension, along the length of the wind tunnel.

Previous work has shown that droplet size distributions vary with distance from the nozzle and therefore, in order to ensure constant distance between nozzle and measurement volume and that the entire spray could be sampled in a minimum of measurement positions, the instrument was moved in an arc at 350 mm from the nozzle with a resolution of

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Projecttitle


MAFFproject code

PA1726

5o. Since there was no upstream equipment to block the air flow, the nozzle could be realigned with the short axis parallel to the air flow. The nozzle was moved at a speed of 0.2 m s -1 across the wind tunnel 20 times for each measurement, which took approximately 250 s.

This measurement scheme, requiring different instrument positions, was extremely time-consuming, restricting the number of measurements that could realistically be made. Thus only one set of measurements were made for each liquid/pressure/windspeed setting.

Previous work has used agricultural spray adjuvants to manipulate spray liquid properties (Butler Ellis and Tuck, 1999, Holloway et al, 2000). Based on these findings, two adjuvants were chosen that have been shown to have a significant effect on spray characteristics. One, a water-soluble tallow amine surfactant (Ethokem, Techsol Ltd), has been shown to reduce droplet sizes and velocities. The second, an insoluble modified soya lecithin (Li-700, Loveland Industries) has been shown to increase droplet sizes and velocities. Both of these adjuvants have been shown to change spray formation mechanisms, with the soya lecithin causing perforation of the liquid sheet formed by a flat fan nozzle and a much shorter sheet, and the surfactant increasing the length of the sheet. Much of the previous work involved a conventional flat fan nozzle with a 110o fan angle and an output of 0.8 litres/min at 3.0 bar. The same nozzle was selected for this work.

1.3 Results and Discussion

Spray formation

Photographs of the liquid sheet formed by the FF110/0.8/3.0 nozzle (11002, Lurmark Ltd, UK) with three liquids (water, 0.5% tallow amine and 0.5% soya phospholipid) show that air speeds up to 8 m s -1 have no effect on the spray formation mechanism, although there is a suggestion that the liquid sheet is slightly shorter at the highest wind speed. Table 1.1 shows the estimated sheet length for the different liquids, pressures and windspeeds. These data are based on only two photographs for each setting and it is therefore not possible to determine their accuracy. However, previous experience suggests that an error of 5 mm is associated with these images, particularly with water-soluble surfactants (Butler Ellis et al, 2001a). The effect of air speed is most marked for the tallow amine surfactant at 1.5 bar.

Table 1.1. Estimated sheet length for three liquids at two pressures and three windspeedsEstimated sheet length, mm, 5 mm

Pressure, bar Windspeed, m s-1 Water 0.5% tallow amine

0.5% soya phospholipid

1.5 0 45 51 161.5 4 44 50 171.5 8 40 45 163.0 0 42 44 193.0 4 42 46 183.0 8 38 40 19

The reduction in length of sheet with increasing air speed suggests that droplet size might increase with air speed, since droplet size is dependent on sheet thickness at breakup (Lefebvre, 1989) and the sheet thins as the distance from the nozzle increases

Measurements of spray characteristics

Initial measurements were made of spray characteristics with a flat fan nozzle operating at 1.5 and 3 bar, spraying the two adjuvants with windspeeds of 0, 4 and 8 m s-1 using the PDIA. The droplet data were analysed to determine volume median diameter (VMD) and total flux (Table 1.2). It was noticed that, although the flow rate of the nozzle is unaffected by windspeed, the total quantity of liquid detected reduced with windspeed. It was thought that this was a consequence of the PDIA operating in diameter-only mode, where a spatial sample is taken. Slower droplets have a higher probability of being detected and therefore account for a higher quantity of the estimated liquid volume than if all droplets travelled at the same velocity. As the wind speed increases, the horizontal velocity of these droplets also increases, reducing the probability of them being detected and reducing the quantity of liquid detected. This was greater at 3.0 bar than at 1.5 bar, because of the wider range of droplet sizes and velocities at 3.0 bar. This is supported by the calculations of VMD which increase with wind speed. A small increase in VMD was anticipated, because of the reduction in sheet length identified but very large increases were observed, which may be due to significantly lower probability of detecting small droplets.

Table 1.2. Variation of total volume of liquid accounted for and Volume Median Diameter (VMD) with windspeed, nozzle pressure and liquid, measured with PDIA.

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Projecttitle


MAFFproject code

PA1726

Liquid Nozzle/Pressure Windspeed Total volume accounted for, % VMD, m0.5% Li-700 FF110/0.8/3.0 at 1.5 bar 0 28.8 250

4 32.3 2948 27.6 337.1

0.5% Ethokem FF110/0.8/3.0 at 1.5 bar 0 51 227.74 46.3 249.88 26.5 281.9

0.5% Li-700 FF110/0.8/3.0 at 3.0 bar 0 35.4 215.94 43.2 243.88 31.8 270.5

0.5% Ethokem FF110/0.8/3.0 at 3.0 bar 0 61.4 194.94 62.6 202.48 36 229.3

There is also a substantial difference in the total volume measured between different liquids when using the PDIA. (Table 1.2) The performance of the PDIA is independent of liquid properties and therefore it must be a consequence of the differences in spray droplet size distribution causing differences in sampling efficiency. The surfactant solution has been shown in previous work to have slower average droplet velocities that will therefore have a higher airborne concentration.

We conclude, therefore, that there are two possible of causes of changes in measured VMD. One is due to a change in droplet size distribution and the other to a change in velocity characteristics. The change in velocity characteristics will lead to a change in droplet size distribution of a spatial sample though not a temporal sample. The consequences of changing either wind speed or spray liquid is likely to affect both velocities and sizes and therefore it is not possible to be sure of the origin of the measured changes in VMD.

It was concluded, therefore, that the use of a temporal sampling technique was preferable in a wind tunnel where wind speeds are comparable with droplet velocities at the measurement point. However, this raises difficulties because the only temporal sampling technique currently available, phase Doppler analysis, cannot necessarily determine droplet sizes accurately when internal droplet structure is present, such as emulsion particles or air inclusions. It has been demonstrated that estimates of absolute flux made with the phase Doppler technique are not accurate (Tuck et al, 1997), although it has been possible to determine relative fluxes at different sampling points during a single measurement period. Similar measurements were made with the phase Doppler analyser using water only to avoid any confounding with spray liquid. Smaller changes in measured volume with wind speed were observed than when using the PDIA (Table 1.3).

Table 1.3. Variation in total volume of liquid accounted for and Volume Median Diameter (VMD) with windspeed and nozzle pressure, measured with a phase Doppler analyser

Liquid Nozzle/Pressure Windspeed Total volume accounted for, % VMD, mwater FF110/0.8/3.0 at 1.0 bar 0 17.5 300.4

2 20.6 297.14 19.5 305.16 18.9 308.48 16.5 320.1

water FF110/0.8/3.0 at 3.0 bar 0 30 218.22 37.7 2324 33.8 233.96 31 233.48 28.4 234.4

However, when a third set of measurements were made, this time including the adjuvants, these liquids showed increases in flux with wind speed (Table 1.4). Although the reason for this is not clear, there are two suggestions. As the wind speed increases, the spray plume becomes dispersed and more sample points are needed. The sampling efficiency of the phase Doppler analyser is likely to go up as droplet density reduces, leading to an increase in volume measured with windspeed. The surfactant solution produces a larger number of droplets, and therefore the sampling efficiency is lower, than with water alone. There is therefore more scope for increasing efficiency as the spray plume becomes less dense. Secondly, when spraying inhomogeneous liquids such as water plus soya lecithin, the rejection rate is higher than when spraying solutions, due to scattering from internal droplet interfaces. This rejection rate may drop when the density of the spray reduces.

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Projecttitle


MAFFproject code

PA1726

Table 1.4. The variation in total volume of liquid accounted for and Volume Median Diameter (VMD) with windspeed and liquid, measured with a phase Doppler analyser

Liquid Nozzle/Pressure Windspeed Total volume accounted for, % VMD, mwater FF110/0.8/3.0 at 3.0 bar 0 53.4 231.9

3 55.2 2296 50.8 243.2

0.5% Ethokem FF110/0.8/3.0 at 3.0 bar 0 48.8 209.83 73.1 216.96 78.9 233

0.5% Li-700 FF110/0.8/3.0 at 3.0 bar 0 42.4 237.93 62 253.96 66.8 254.5

Data obtained from phase Doppler analysis suggests that droplet size increases with wind speed, although the size of the increase is significantly lower than data from the PDIA.

Clearly, there is doubt about whether sampling biases that change with windspeed allow the spray droplet size to be accurately determined with either of the instruments used in this study. However, at a given windspeed, it should be possible to compare different liquids although the differences may be increased or reduced by sampling biases. The most reliable technique would probably be to use an instrument such as the PDIA that is independent of spray liquid and has a sample rate that is independent of spray density, but make simultaneous measurements of velocity so that a temporal distribution can be calculated. Measurements have been made with alternative instruments in air flows with both an optical imaging probe (Bouse et al, 1990) that is liquid-independent and with spatially sampling technique that uses laser diffraction (Teske & Thistle, 2000, Sanderson et al, 1997) but in these cases, the air velocities were significantly higher than droplet velocities so that the droplet velocity was likely to be independent of droplet size and temporal and spatial samples would have been the same.

Tables 1.2 and 1.4 show that the effect of liquid is therefore the same as was established in still air with a slowly moving flat fan nozzle in previous work. There is no suggestion that the differences between liquids reduce as wind speed increases. It was not possible, however, to evaluate the effect of air flow on the characteristics of sprays produced by air inductions nozzles, because of the difficulties associated with sampling complex droplets. Further work is needed to develop methods of obtaining temporal samples with a liquid-independent technique such as PDIA.

1.4 Conclusions

Measurement of spray droplet size distributions in an air flow with velocities comparable with those occurring in boom spraying applications is not straightforward. Spatial sampling techniques are likely to give larger increases in droplet size due to changes in droplet velocity profiles than temporal sampling techniques. It is suggested that a temporal sampling technique, such as that provided by phase Doppler analysis, might provide the most representative measure of spray leaving the nozzle. However, there are difficulties associated with measuring different liquids and air-included droplets because of the dependence of light scattering on droplet structure.

Observations of spray breakup and measurements of droplet size with two different instruments showed no evidence to suggest that the mechanisms controlling spray formation with hydraulic flat fan nozzles are affected by air speeds up to 8 m s-1. We conclude, therefore, that measurements made in still air are a good indication of droplet size distributions in an air flow.

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2. Measurement of the effect of spray liquid on spray drift

2.1 Introduction

Many investigations have shown that spray liquid properties influence the characteristics and performance of sprays produced by agricultural nozzles (Miller & Butler Ellis, 1997). Formulation type is an important factor in determining the nature of the effect (Butler Ellis et al, 1999, 2001a). There is also a well-established correlation between spray droplet size and spray drift, particularly when considering a single nozzle design, such as the flat fan nozzle. Although it would seem likely that the same correlation occurs when the change in spray characteristics results from a change in spray liquid, and there is a limited amount of evidence to suggest that this is so (Western et al, 1999, Butler Ellis et al, 1998). It has been shown (Butler Ellis et al, 1997) that spray structure and droplet velocities are also affected by spray liquid, both of which also influence spray drift (Smith and Miller, 1994). Predictions of drift from boom sprayers based solely on spray droplet size are not necessarily valid.

It has been hypothesised that water-soluble formulations containing surfactants, which reduce droplet size and velocity, will increase drift, whereas emulsion-forming formulations (EC and EWs), which increase droplet size and velocity, will reduce drift. The work described in this paper aimed to test these hypotheses and to establish whether droplet size distributions can be used to predict drift with different formulation types.

2.2 Materials and Methods

Test liquids

It has been shown that the degree to which a surfactant influences spray characteristics is very variable (Butler Ellis et al 2001a), and it is not yet possible to measure surfactant properties and predict the likely effect. Five surfactants were selected to evaluate the range of effects on spray drift with a conventional flat fan nozzle in order to select one with a measurable and representative effect. Following this, a blank EC formulation and the combined EC and surfactant were also tested. A single EC formulation was considered sufficient for this investigation because the effect of all types of emulsion was very consistent between nozzles and formulations (Butler Ellis et al, 1999). Spray liquids are shown in Table 2.1.

Table 2.1. Spray liquidsName Description ConcentrationAgral Non-ionic nonyl phenol ethoxylate 0.1%Ethokem Cationic tallow amine ethoxylate 0.5%Synperonic 91/8 Non-ionic surfactant; C9/11 alcohol 0.1%Polyfon H Anionic dispersant; Sodium lignosulfonate 0.1%Frigate Cationic tallow amine ethoxylate 0.5%EC Blank emulsion concentrate 0.5%EC + Ethokem Both at 0.5%

Nozzles

Previous work investigating the effect of spray liquid on spray characteristics used a range of “02” size hydraulic nozzles, including a flat fan, low drift (pre-orifice), and hollow cone. These same nozzles were selected to investigate the effect on drift, together with an “02” size air induction nozzle. Nozzles are shown in Table 2.2.

Table 2.2 Spray nozzlesNozzle type Specification ManufacturerFlat fan FF/110/0.8/3.0 LurmarkHollow cone HC/0.71/3.0 LurmarkLow drift (Pre-orifice) FRD110/0.8/3.0 LurmarkAir Induction AI 110 02 VS Spraying Systems

Drift Measurement

Vertical and horizontal profiles of airborne spray were measured in a wind tunnel using the techniques described by Walklate et al, 2000. Polythene collecting lines of 2mm diameter were positioned across the working section of the wind tunnel, 10cm above the floor at 1m intervals between 2 and 7 m downstream of the nozzle for the horizontal profile and at 2m downwind of the nozzle at 10cm intervals for the vertical profile. A tracer dye (“Green S”) was added to the spray liquid at a concentration of 0.2%, and the quantity of dye recovered from collecting lines used to determine the quantity of spray deposited.

Projecttitle


MAFFproject code PA1726

Measurement of spray droplet size distributions

A Malvern Particle Sizer 2600 was used to measure droplet size distributions with four nozzles and four spray liquids. The nozzle traversed across the laser beam to produce an average distribution of the whole spray footprint. The Volume Median Diameter (VMD) was determined for all nozzles and the percentage liquid volume in droplets less than 100 m was determined for all but the air induction nozzle, where air inclusions prevent the measurement of liquid volumes.


The horizontal drift profiles for the water-soluble surfactants, measured at 2 m/s wind speed are shown in Fig. 2.1. All surfactants produced similar profiles, although, contrary to expectation, did not have significantly higher levels of drift than water alone, and at distances greater than 2m from the nozzle, appeared to reduce drift.

Fig. 2.1 Horizontal drift profiles for a standard flat fan nozzle and five surfactants

Similar trends were shown by the vertical profiles, with most surfactants resulting in lower levels of airborne spray than water alone. Previous work (Butler Ellis & Tuck, 1999) showed that the tallow amine surfactant Ethokem reduces droplet size and velocities when sprayed through most hyraulic nozzles. Since the results above showed that Ethokem also had one of the highest levels of drift of all the surfactants tested, it was selected for further investigations with a wider range of spray nozzles.

Effect of formulation type

Horizontal drift profiles at both windspeeds for all four nozzles showed there was clearly an interaction between the formulation and the nozzle design since the trends are not the same with all four nozzles. However, the EC alone resulted in the lowest drift for all four nozzle at both wind speeds, as would have been predicted from measurements of spray characteristics. Adding a surfactant to the EC had the effect of slightly increasing the airborne spray, but in general this combination behaved in a similar way to water alone or the EC.

The greatest effect occurred with the spray liquid containing only a water-soluble surfactant, but this was apparent only at the higher wind speed. At 2 m/s, differences were significant only at 2m down wind. The total collected airborne spray 2 m down wind, calculated from the vertical profiles, are shown in Tables 2.3 and 2.4.

Results shown in Tables 2.3 and 2.4 suggest that the flat fan nozzle is relatively insensitive to spray liquid at 2 m/s but becomes highly sensitive to water-soluble surfactants at 4 m/s. The hollow cone nozzle is not sensitive to the presence of water-soluble surfactants but had significantly lower levels of drift with an EC formulation. The low drift nozzle was sensitive only to water soluble surfactant, particularly at 4 m/s. The air induction nozzle was sensitive to both formulation types at both wind speeds, but overall levels of drift were so low that increases in airborne spray as a result of formulation changes were of no practical significance. The relative levels of drift for the four nozzles depended on the liquid sprayed and the wind speed, which has important implications for drift classification.

Table 2.3 Total airborne spray, % nozzle output, 2m downwind, wind speed 2 m/sNozzle water 0.5% surfactant 0.5% EC 0.5% EC + 0.5% surfactantFlat fan 8.94 8.17 5.10 9.27Hollow cone 8.94 8.24 1.50 3.68

9

0.0

10.0

20.0

30.0

40.0

50.0

60.0

2 3 4 5 6 7Distance from nozzle, m

Airb

orne

spr

ay,

% n

ozzl

e ou

tput

water 0.1% Agral0.5% Frigate 0.1% Synperonic0.1% Polyfon H 0.5% Ethokem

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Low drift 4.42 6.50 3.27 3.75Air induction 0.81 2.00 0.37 0.54

Table 2.4 Total airborne spray, % nozzle output, 2m downwind, wind speed 4 m/sNozzle water 0.5% surfactant 0.5% EC 0.5% EC + 0.5% surfactantFlat fan 15.01 32.09 16.04 19.20Hollow cone 20.97 21.98 6.65 17.40Low drift 9.01 23.38 8.15 10.51Air induction 2.05 5.55 1.32 2.29

The horizontal profiles were analysed to produce a length scale, compared to an 03 reference nozzle FF110/1.2/3.0 operating at 3.0 bar spraying 0.1% Agral, in the same way that a LERAP star rating calculation would be carried out (Walklate et al, 2000). This is shown in Table 2.5 and suggests different conclusions for flat fan and hollow cone nozzles from those that might be drawn from the raw data. The surfactant and EC formulations increased length scales with the flat fan nozzle and all formulations significantly reduced length scale with the hollow cone nozzle.

Measurements of spray droplet size distributions were analysed to determine VMD and the percentage of liquid volume contained in droplets less than 100 m, shown in Table 2.6. There was not a good correlation between characteristics of spray droplet size and the total airborne spray, either at 2 or 4 m/s apart from with the low drift nozzle, suggesting that measurements of spray droplet size is not a good indicator of spray drift. Previous work with conventional (Hobson et al, 1993) and air induction nozzles (Butler Ellis et al, 2001b) suggested that the drift is strongly related to droplet size distributions. However, this was established only for different nozzles of similar design spraying the same liquid, where velocities and spray structure are comparable, not for a range of spray liquids.

Table 2.5 Drift length scale, m, calculated from horizontal profiles at 2 m/s windspeedNozzle water 0.5% surfactant 0.5% EC 0.5% EC + 0.5% surfactantFlat fan 6.5 8.0 7.3 6.6Hollow cone 21.9 12.9 16.5 8.7Low drift 7.7 9.9 6.3 6.7Air induction 4.9 6.1 1.4 2.0

Table 2.6. Spray characteristics measured with a Malvern Particle AnalyserNozzle Water Surfactant EC Surfactant + EC

VMD, m

%<100 m

VMD, m

%<100 m

VMD, m

%<100 m

VMD, m

%<100 m

Flat fan 159 15.9 149 20.5 175 12.6 156 16.6Hollow cone 209 1.8 198 2.4 227 2.9 196 2.6Low drift 198 8.6 185 10.9 217 6.4 197 7.8Air induction 503 - 369 - 487 - 426 -

It can be seen that the effect of spray liquid on spray drift depends on which measure of spray drift is chosen, and therefore it is not possible to deduce that surfactants increase drift and emulsions reduce drift with all nozzles. In addition, comparing the levels of drift with different nozzles shows that the spray liquid is crucial. For example, using total airborne spray 2 m downwind of the nozzle as the measure of spray drift, the hollow cone nozzle has similar drift risk to a conventional flat fan nozzle spraying water, but considerably less when spraying an EC formulation. This has implications for protocols for classifying spray nozzles for drift as in the BCPC revised scheme (Miller et al, 2002) or for LERAP assessments. It should be noted that many of the measurements reported in this paper were made with relatively high levels of surfactant (0.5%) whereas drift classification protocols recommend 0.1% when any effect is likely to be much smaller. In terms of assessing a particular spray generator for its drift potential, the use of 0.1% surfactant probably represents an “average”spray liquid, although the robustness of this assumption ought to be tested.

2.4 Conclusions

The physical properties of the spray liquid have been shown to significantly influence both horizontal and vertical drift profiles measured in a wind tunnel, with increases in total airborne spray of up to 150%, compared with water alone, being measured. Although a limited number of spray liquids were tested, it is suggested that spray liquids that are

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emulsions are likely to reduce measures of spray drift, particularly with low drift and air induction nozzles, although this effect will be reduced if there is a significant level of surfactants present. Water-soluble formulations potentially increase drift if surfactants are present, but the degree to which this occurs depends upon nozzle design and wind speed. The correlation between percentage spray volume contained in droplets smaller than 100 m and spray drift was not good, particularly for the flat fan and hollow cone nozzles, suggesting that estimates of drift potential for different spray liquids based solely on droplet size distributions would not be accurate.

Comparison between different nozzles in terms of spray drift depends upon (a) which spray liquid is used and (b) which measure of spray drift is used. The use of 0.1% water-soluble surfactant in drift classification protocols is likely to represent a typical spray liquid with a representative drift performance. However, when making environmental risk assessments, the importance of including some information relating to spray liquid properties is crucial since the measures of drift can be increased to 270% or reduced to as low as 17% of the levels obtained when spraying with water alone.

3. Investigations of the effect of spray liquid on deposition in crop canopies

The biological performance of plant protection products applied using arable boom sprayers depends on many factors including product formulation and the resulting physicochemical properties of the spray liquid. Performance can be improved by increasing the quantity of the plant protection product that is deposited on the plant, although there is not always a strong correlation between total active ingredient retained on the plant and efficacy. This is most probably because the distribution of the deposit over the plant, in terms of size and number of droplets and penetration into the canopy, can be equally important (Knoche, 1994). In order to improve targeting of the spray, it is important to know how formulation/liquid properties affect spray deposition. This is also influenced by the characteristics of the target plant itself. Surface properties and plant structure, both of which will change as the plant grows, will affect the quantity of spray deposited and its distribution over the plant. Interpreting whole plant retention data can be difficult. For young plants there are few plant growth and canopy effects to consider. However, for older plants whole plant retention will be the result of the combined effect of leaf surface, plant growth and canopy density (Anderson et al, 1987). As the plants grow larger and the canopy becomes denser, the effective spray target become larger and more spray droplets will be intercepted. In particular, droplets bouncing from leaves on their first impact will have a higher probability of being retained on other leaves.

Not only does plant structure change with age, but so do the surface properties of leaves. For example, the wettability of wheat, barley and oat leaves have been shown to increase as growth stage increases from 15 to 80, resulting in ten-fold increases in water deposited on single horizontal leaves (Henning-Gizewski and Wirth, 2000). A single plant will have leaves with a range of ages and therefore a range of wettabilities. It is, therefore, difficult to determine from whole plant retention data the relative contributions of the individual effects. At the highest canopy densities it is likely that differences in retention between spray liquids will be smaller than at low densities

Many previous studies, where the effect of a wide range of liquid types on spray deposition on cereals or grass weeds have been investigated, have used indoor-grown plants, generally at early growth stages. While such plants may be reasonably representative of small outdoor-grown plants, it is unlikely that they will be representative of larger outdoor-grown plants in a canopy.

Some previous work on outdoor-grown plants using a range of spray liquid properties showed increased retention by up to 4 times that of water alone (Dempsey et al, 1985, Anderson et al, 1997). In contrast, other measurements showed no significant differences in retention between liquids (Robinson et al, 2001)

Similar studies on indoor-grown plants have shown that much larger increases in deposition are possible. A study of the retention of different types of adjuvants and a 1:1 acetone-water mix, on young indoor-grown beans, peas and barley (Holloway et al, 2000) showed that the effect of spray liquid was far greater on the least wettable leaf surfaces (i.e. greater on barley than on beans). Water always gave the lowest retention, the maximum retention was up to 6 to 8 times that of water and there was a consistent trend for retention to increase as dynamic surface tension of the spray liquid decreased. Other studies using different spray liquids have found similar behaviour for indoor-grown wheat and oat plants (Grayson et al, 1996; de Ruiter et al, 1990).

Dynamic surface tension of the liquid appears to have dominated retention behaviour in a wide range of investigations, using both indoor and outdoor plants and individual leaves (Holloway et al, 1994, Stevens et al, 1993, Anderson et al, 1987, Webb, 2000) . The major exception to this is with some polymeric additives, where the extensional surface viscosity causes retention to be higher than would be expected from the dynamic surface tension alone (Richards et al, 2000; Wirth et al, 1991).

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A further factor which is known to influence spray deposition is the application system, since this can significantly affect the characteristics of the spray. The quantity of spray liquid retained will depend not only on plant characteristics and liquid properties but also droplet size and velocity distributions and application volume rates. Many experiments to investigate the effect of liquid properties on retention use a single application rate and equipment not commonly used in the field (Holloway et al 1994, Holloway et al, 2000, Anderson et al, 1987) or even single droplet generators (Webb, 2000). It is possible that the extent to which liquid properties affect deposition could be influenced by the particular application system used. For example, the fine spray produced by an FE/0.6/3.0 nozzle used in some retention experiments (Holloway et al, 1994, Holloway et al, 2000) would be better retained than the coarser sprays used in practice, and therefore have less scope for improving retention by manipulating spray liquid.

The aim of this part of the project was to examine the effect of liquid properties in a range of situations representative of practical pesticide application. Outdoor-grown wheat plants, sown at two rates, with growth stages between GS 22 and GS 35 when many fungicides and growth-regulators are sprayed, were used. Both conventional hydraulic and air induction nozzles, of sizes used in field application, were included. A range of spray liquid physical properties were obtained from using different chemical types of agricultural adjuvants and formulated products at field rates in water. Since total retention is affected by leaf surface as well as plant growth and canopy density, the experiments included spraying both single leaves and groups of plants.

The main objective was to test the hypothesis that the effect of spray liquid on retention in the field will be different from that measured in laboratory tests with single indoor-grown pot plants, and in particular that as canopy density increases, the difference between liquids reduces.

3.2 Methods

Experiment 1.

Outdoor-grown wheat (Triticum aestivum cv Axona), were grown from seed in 78 x 40 cm trays with 4 rows, each 10 cm apart, per tray with 22 seeds, each 3.5 cm apart, per row. They were sprayed at GS 30-33 and with 2200 stems m-2.

Two nozzles were used, a flat fan FF110/1.2/3.0 (03F110, plastic, Lurmark) and air induction AI110/1.2/3.0 (03Bubblejet, plastic, Billericay Farm Services) both at 2.0 bar pressure and 5.5 km h -1 forward speed giving a nominal 200 l ha-1. They were mounted on a track sprayer, 0.5m apart on a 3-nozzle boom section with the nozzles 0.5m above the top of the plants. A selection of the liquids described in Table 3.1 were used singly and in mixtures (Table 3.2). All spray solutions contained sodium fluorescein (BDH, Poole, UK) at concentrations between 0.05 and 1 g l-1.

A set of “guard” plant trays surrounded the sample tray to create a uniform canopy around the sampled plants. These guard trays remained the same throughout the experiment. Four individual leaves were excised from similar plants and sprayed with the same liquids using only the flat fan nozzles. The leaves were held horizontally, and as flat as possible, ca 0.3 m above the ground by small clips on metal supports.

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Table 3.1 Liquid composition details for all experiments.Name in text Type Formulation Concentration

( g litre-1 )

water Water tap water -

acetone-water Acetone-water acetone and water 1:1 by volume -

mineral oil Emulsifiable aEC: 968 g kg-1 mineral oil 10oil 32 g kg-1 emulsifiers

methylated oil Emulsifiable bEC: 750 g kg-1 methylated rapeseed oil 10oil 250 g kg-1 emulsifiers

tallow amine Surfactant cSL: 870 g l-1 polyethoxylated tallow amine 5

nonylphenol Surfactant dSL: 948 g l-1 polyethoxylated nonylphenol 1

organosilicone Surfactant eSL: 800 g kg-1 polyethoxylated heptamethyl trisiloxane

1.5

phospholipid Phospholipid fEC: 350 g l-1 modified soya lecithin 5 350 g l-1 propionic acid 100 g l-1 polyethoxylated alkylphenol

EC Blank EC gEC: 50 g l-1 calcium dodecylbenzene sulphonate

5

50 g l-1 unsaturated fatty acid esterSolvesso 200 added to give 1 litre total

a Actipron (ADJ 0013h); b Phase (ADJ 0279 h); c Ethokem (ADJ 0353 h); d Agral (ADJ 0154 h); e Silwet L-77 (ADJ 0193 h); f Li-700 (ADJ 0176 h); g supplied by Aventis (Agrevo)h The Pesticides Register Revised Adjuvants List, October 2001 Supplement, Pesticides Safety Directorate, York, UK

A block of four replicate polypropylene discs (Sonoco, Slough, UK; area 2102 mm2) were used to record spray deposition per unit ground area. They were aligned with the sampled plants or leaves, mounted on a flat plate and sprayed after the plants or leaves in each single run. The treatments in each experiment were run in a randomized order.

Each liquid/nozzle combination was sprayed once, with three sets of six plants sampled at random for each combination. Plants, leaves and discs were sprayed, allowed to dry in a low light area, and sampled within 6 hours of spraying. All plant samples were from the middle two rows of the tray, with the row ends avoided. Samples and discs were washed in between 20 to 100 ml of alkaline solution (20 g l-1 sodium hydroxide, 5 g l-1 Triton X100), using enough for effective washing. The sodium fluorescein content of the resulting sample solutions was measured with a Perkin Elmer LS-2 spectrophotometer. Liquid from the spray solutions was diluted and measured in the same way. Washed plant material was dried (ca 48 hours @ 95oC) and weighed. The area of washed leaf material was measured (Optimax 4 image analyser) then bulked, dried and weighed.

Experiment 2.

Three liquids, the tallow amine, EC and water were used to represent high, medium and low retention, respectively . The same flat fan nozzles were used, but at 3.0 bar pressure and 8 km h -1 forward speed giving a nominal 180 l ha-1

(representative of field practice). Air induction AI110/1.2/3.0 (03 AI Teejet, plastic, Spraying Systems) nozzles were used at the same pressure, forward speed and application volume, producing a larger droplet spray than the air induction nozzles used in experiment 1. Two test trays were used, with different sowing densities and stem numbers to examine the effect of different canopies on retention. The plants were outdoor-grown wheat (cv Axona) sown at the same density as experiment 1 and at half density (11 seeds, each 7 cm apart, per row). A split-plot experimental design was used to give robust replication and examine variability of retention in more detail. In test 1, plants were at GS 22-26 with either 1540 (half density sowing) or 2640 (full density sowing) stems m -2. Each liquid/nozzle combination was sprayed four times, with six single plants sampled for each combination, making a total of 24 replicate samples. No single leaves were sprayed.

In test 2, plants were at GS 30 with either 1540 or 660 stems m -2. The 1540 stems m-2 plants were from the same half density sowing as test 1, while the 660 stems m -2 plants were a thinned set (4 plants per row, each 13 cm apart) from the

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same full density sowing as test 1. Each liquid/nozzle combination was sprayed three times, with six single plants and two single leaves sampled for each combination, making a total of 18 replicate plant samples and six replicate leaf samples.

Measurements

Retention on plants was measured and normalized by spray volume applied and plant dry weight i.e. as the amount of liquid retained l) per 100 l ha-1 applied and per g dry weight of plant material. Some measurements were also normalized by spray volume applied only, to examine the effect of plant bulk on normalization.

Retention on leaves was measured normalized by spray volume applied and leaf area i.e. as the amount of liquid retained (l) per 100 l ha-1 applied per cm2 of leaf area. This is simply related to the percentage of applied liquid retained on the leaf by the formula:

% applied liquid retained = 100 *l retained per 100 l ha-1 applied per cm2 leaf area

Since absolute values of retention depend on many factors, the effect of spray liquid can best be assessed by considering the retention with a spray liquid relative to that with water alone. Statistical analysis on whole experiment data sets was performed using Genstat (ver. 5.0, Lawes Agricultural Trust) with significance tests performed at the 5% level.


Experiment 1

Retention on outdoor-grown wheat for the full range of liquids used in experiment 1 are shown in Tables 2.2 and 2.3. There were some differences in the ranking order of the different liquids between whole plants and individual leaves, but the trends were similar. The maximum retention in both cases was with acetone-water, giving 2.2 times the quantity of water retained on single leaves, but only 1.25 times the quantity of water retained on whole plants with the standard flat fan nozzle. This contrasts with a figure of around eight times the quantity of water retained on indoor-grown pea and barley plants with an evenspray nozzle (Holloway et al, 2000). Lower levels of retention were obtained with the air induction nozzles, and larger increases with acetone-water (1.7 times water alone) than with the conventional flat fan nozzle. The retention w.r.t. water for different liquids sprayed with either nozzle type were much smaller for the outdoor grown wheat plants than for indoor grown barley plants with single liquids (Fig. 3.1) or mixtures and were closer to those for indoor grown bean plants.

Table 3.2 Retention for outdoor-grown wheat at GS 30-33 and 2200 stems m-2 (Experiment 1).FLAT FAN NOZZLES AIR INDUCTION NOZZLES

Liquid Volume Retention Volume Retentionapplied average (sem) significance applied average (sem) significance (l ha-1) (l /100 l ha-1/g) band (l ha-1) (l /100 l ha-1/g) band

acetone-water 179 20.2 (1.70) a 167 17.7 (2.03) a b c dEC + phospholipid 197 18.0 (0.52) a b 168 15.3 (0.38) b c d e f gphospholipid 194 17.6 (0.71) a b c 172 14.7 (1.26) d e f g hEC 184 16.4 (0.78) b c d e 196 10.3 (0.48) lEC + methylated oil 199 16.3 (0.75) b c d e 168 13.8 (0.37) e f g h iEC + mineral oil 184 16.2 (0.80) b c d e f 169 13.5 (0.08) f g h iEC + nonylphenol 189 16.4 (2.19) b c d e f 174 10.3 (0.96) lwater 194 16.1 (0.43) b c d e f 195 11.0 (0.49) k lmineral oil 185 15.5 (1.04) b c d e f g 173 12.4 (0.35) h i j knonylphenol 181 14.8 (1.04) c d e f g h 207 11.2 (0.34) j k lmethylated oil 195 14.3 (1.27) e f g h 156 13.9 (1.31) e f g h iorganosilicone 190 13.3 (0.66) g h i j 171 9.8 (0.38) lEC + organosilicone 183 11.8 (0.55) i j k l 188 11.2 (0.04) j k l

Statistical analysis combined both nozzles using loge transformed values.

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Table 3.3 Retention for horizontally held excised single leaves of outdoor-grown wheat at GS 30-33 (experiment 1).

FLAT FAN NOZZLESLiquid Volume Retention

applied average (sem) significance (l ha-1) (l /100 l ha-1/cm-2) band

acetone-water 192 0.84 (0.08) aEC + methylated oil 203 0.66 (0.09) bmethylated oil 217 0.61 (0.03) bnonylphenol 203 0.61 (0.05) borganosilicone 203 0.54 (0.05) b cEC + nonylphenol 191 0.53 (0.06) b cphospholipid 199 0.51 (0.03) b c dEC + organosilicone 202 0.51 (0.07) b c d eEC + phospholipid 187 0.50 (0.07) b c d eEC + mineral oil 185 0.46 (0.04) b c d eEC 194 0.40 (0.03) c d emineral oil 193 0.37 (0.03) d ewater 220 0.38 (0.08) e

Statistical analysis used loge transformed values.

0

1

2

3

4

5

6

7

indoor barley indoor bean outdoor wheat 2200stems FF

outdoor wheat 2200stems ABJ

acetone-water nonylphenol EC phospholipid

Fig. 3.1 Retention of single liquids on indoor-grown barley and bean2 and on outdoor-grown wheat.Indoor barley, bean: evenspray nozzle (FE80/0.6/3.0),1.9 bar, 1.6 km h-1, nominal 200 l ha-1. Outdoor wheat: flat fan FF110/1.2/3.0 (FF) and air induction AI110/1.2/3.0, (ABJ) 2.0 bar, 5.5 km h-1, nominal 200 l ha-1.

Experiment 2

The retention on plants at different sowing densities and stem numbers for both flat fan and air induction nozzles obtained from experiment 2 is given in Tables 3.4 and 3.5, and retention on horizontally held excised single leaves for both flat fan and air induction nozzles is given in Table 3.6. At the highest plant density, there were no significant differences between liquids or nozzles. At lower densities, some differences were significant, and the retention with the tallow amine relative to water varied from 1.5 to 1.7. This contrasts with indoor peas and barley, where the retention with tallow amine relative to water was 7.2 and 5.7 respectively. Retention on individual leaves showed greater increases, with retention of tallow amine relative to water of 2.8 with the flat fan nozzle and 7.3 with the air induction nozzle.

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Table 3.4 Retention for outdoor-grown wheat at GS 22-26 and 1540 or 2640 stems m-2 (experiment 2, test 1).FLAT FAN NOZZLES AIR INDUCTION NOZZLES

Liquid Volume Retention Volume Retentionapplied average (sem) significance applied average (sem) significance (l ha-1) l /100 l ha-1/g) band (l ha-1) l /100 l ha-1/g) band

1540 stems m-2

tallow amine 158 53 (4.32) a 185 45 (2.42) a bEC 149 48 (3.13) a 169 37 (1.91) b cwater 150 38 (2.01) b c 178 29 (1.98) d

2640 stems m-2

tallow amine 158 37 (3.10) bcd 185 32 (2.19) cdEC 149 37 (1.52) bc 169 31 (1.61) cdwater 150 35 (1.30) cd 178 31 (2.34) cd

Statistical analysis combined both nozzles and both stem numbers using loge transformed values.

Table 3.5 Retention for outdoor-grown wheat at GS 30 and 660 or 1540 stems m-2 (experiment 2, test 2).FLAT FAN NOZZLES AIR INDUCTION NOZZLES

Liquid Volume Retention Volume Retentionapplied average (sem) significance applied average (sem) significance (l ha-1) (l /100 l ha-1/g) band (l ha-1) (l /100 l ha-1/g) band

660 stems m-2

tallow amine 149 45 (4.99) a 169 38 (1.88) a bEC 146 35 (2.75) b 173 26 (1.94) dwater 152 28 (2.87) d 165 25 (1.66) d

1540 stems m-2

tallow amine 149 34 (2.35) b c 169 29 (1.89) c dEC 146 27 (1.93) d 173 20 (0.74) ewater 152 20 (0.94) e 165 20 (1.03) e


Table 3.6 Retention for horizontally held excised single leaves of outdoor-grown wheat at GS 30 (experiment 2 test 2).FLAT FAN NOZZLES AIR INDUCTION NOZZLES

Liquid Volume Retention Volume Retentionapplied average (sem) significance applied average (sem) significance (l ha-1) (l /100 l ha-1/ cm-2) band (l ha-1) (l /100 l ha-1/ cm-2) band

tallow amine 144 0.91 (0.074) a 171 0.73 (0.061) a bEC 135 0.58 (0.045) b 160 0.23 (0.020) cwater 141 0.32 (0.076) c 166 0.10 (0.006) d


Effect of leaf surface on retention

Retention on single leaves should reflect the leaf surface properties without the complication of plant and canopy growth factors. These experiments gave larger differences in retention between liquids on single leaves than were measured on the whole plants that the leaves came from. This was true for both flat fan and air induction nozzles. Also, there were more statistically significant differences in retention between water and other spray liquids (Table 3.3 cf Table 3.2). However, these differences between liquids on single leaves were still smaller than for young indoor-grown barley plants.

This indicates that the young (GS 11-15) barley plants had more water-repellent leaf surfaces than the older (GS 30-33) wheat plants. This is confirmed by a previous study (Henning-Gizewski and Wirth, 2000) which found that single leaves from wheat at GS30 retained 3 to 6 times more water than single leaves from barley at GS15, with single leaves from wheat at GS 30 retaining around 22 % of a water spray. In our experiments the retention on single leaves from wheat at GS 30-33 was between 32 and 38 %. This is reasonable agreement given that different cultivars were used in the study

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and in our work. Retention on different cultivars has been found to be highly variable, with the highest retention up to double the lowest (Combellack and Richardson, 1985)

Canopy density

Assessing the effect of canopy density requires careful analysis, since it involves plant size, plant weight, plant morphology and canopy structure. When the canopy was at its densest, i.e. 2640 stems m -2, Leaf Area Index (LAI) >7, application method and liquid property effects on whole plant retention became very small and retention was almost a constant. This indicates that a high percentage of the spray is retained on the plants, with little deposition on the ground. This would agree with a previous study of soil deposits under different canopies which measured soil deposits of only 7 % of the applied spray in a wheat crop with a LAI of 6 compared to 20 % soil deposits at a LAI of 4 (Gyldenkaerne et al, 1999).

At canopy densities lower than 2640 stems m -2 there was a clear ranking of liquid retention for both nozzles, with tallow amine retention higher than EC, and EC retention higher than water. These differences were mostly statistically significant. Flat fan nozzles gave higher retention than air induction nozzles (averaged over all data, flat fan nozzles gave 20 % higher retention than the air induction nozzles), with the differences more likely to be significant with lower plant densities and with the EC formulation.

Dynamic surface tension of the spray liquid

Indoor plants gave a high correlation (R2 = 0.96) between increasing retention and decreasing dynamic surface tension (DST), with a strong relationship between the two2. Retention on single leaves from outdoor plants was also highly correlated with reduced dynamic surface tension (R2 = 0.96), but with a lower gradient indicating a smaller effect. Outdoor plants gave a weak trend for a small increase in retention with decreasing dynamic surface tension with both nozzles, reflecting the lack of differences in retention between liquids found for outdoor-grown wheat leaves (Fig. 3.2). Although the correlation between retention and DST for flat fan nozzles was still good (R2 = 0.71), for air induction nozzles, it was relatively poor (R2 = 0.42).

0.51.01.52.02.53.03.54.04.55.05.56.06.5

30 35 40 45 50 55 60 65 70 75dynamic surface tension, 50ms surface age (mN m-1)

indoor barley outdoor plant 2200 stems FF outdoor plant 2200 stems ABJ outdoor leaf FFFig. 3.2. Retention of single liquids as a function of dynamic surface tension for indoor-grown barley and outdoor-grown wheat plants and leaves with flat fan (FF) and air induction (ABJ) nozzles.

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The combined effects of plant surface, canopy density, application method and dynamic surface tension of the spray liquid

The reduction in differences in retention between liquids for older, outdoor-grown plants when compared to younger, indoor-grown plants result from three main effects.

Firstly, leaf surfaces become less water-repellent with age and outdoor-grown plants are less water-repellent than indoor grown plants, both of which will reduce the effect of dynamic surface tension. Secondly, as plants grow, the increasing canopy density creates a larger target area that intercepts more of the spray droplets. Liquids with a low dynamic surface tension are well retained at their first impact with the plant, while a high proportion of droplets of water and other liquids with a high dynamic surface tension, bounce off or shatter on their first impact with the plant. In an open canopy these droplets will be lost, whereas in a more dense canopy, they will be intercepted by other leaves and retained. Older plants in denser canopies have more leaves to intercept droplets bouncing or shattering on their first impact with the plant, resulting in increased retention due to increased canopy density for water and other high dynamic surface tension liquids. At the extreme, the canopy density is high enough to give similar retention for all liquids e.g. the data for 2640 stems m -2.

The young indoor-grown barley plants had a highly water-repellent surface, were small, vertical targets and were placed sprayed directly underneath an 80o evenspray nozzle which presented essentially vertical droplet trajectories to the plant. This was a relatively challenging target on which to deposit spray droplets, compared with the field situation. The use of overlapping 110 o nozzles in the present study gave a wider range of droplet trajectories that are more likely to be intercepted by vertical plant growth and therefore spray liquid might be expected to be less important. Where retention was reduced, for example through the use of an air induction nozzle, the potential for liquid to increase retention was greater. Although it has been suggested that liquid properties dominate application technique in determining levels of retention (Stevens et al, 1993), the data presented here suggest that changes in application technique can result in changes in retention of a similar size to those caused by changes in spray liquid. The combination of increased plant surface wettability and increased effective target size reduces the effect of spray liquid compared that found in indoor plant studies

Assessment of the effect of a cross-wind on deposition patterns for different formulations

Since the effect of spray liquid on deposition is small when canopy structure dominates, the addition of a cross-flow is likely to further reduce the measured differences between spray liquids. It was thought, therefore, that conducting an experiment to assess the interaction between spray liquid and cross flow was unlikely to result in measurable effects. However, work undertaken simultaneously in DEFRA – funded project PA1725 has shown that spray characteristics are important in determining the influence of induced airflows around the sprayer boom and cross flows on deposition patterns (Webb et al, 2002). Low-drift sprays, such as those produced by air induction nozzles, are much less influenced by air flows around the boom than are higher-drift sprays, such as the conventional fine spray, resulting in lower peaks caused by tractor wake and less of a “swath shift” due to a cross wind. It is likely, therefore, that spray liquids that are known to reduce drift, such as emulsion-forming formulations, will have a similar effect. Emulsions would be expected to have small central peaks and similar upwind and downwind distributions, whereas surfactant solutions that are more susceptible to drift will have larger peaks and greater differences between upwind and downwind swaths.

3.4 Conclusions

Previous studies of indoor and outdoor grown plants have observed that retention increased with decreasing dynamic surface tension, with the maximum retention 4 to 8 times that of water. For a given nozzle, liquid properties dominated droplet size effects on retention.

Retention on outdoor wheat plants at GS30-33 was strongly influenced by plant growth, canopy properties and application technique. The effect of dynamic surface tension was much less than on young, indoor plants where leaf surfaces were more water-repellent. This resulted in higher levels of retention of water and other high dynamic surface tension liquids on outdoor-grown single leaves than indoor-grown leaves. The increased probability of droplets hitting foliage in a denser canopy further reduced the differences in retention between liquids when compared with younger plants. At its most extreme very high canopy density (LAI > 7) caused retention for all liquids to be similar.

Air-induction nozzles gave on average 20 % less retention than flat fan nozzles, although this difference was largest for high dynamic surface tension liquids. This suggests that their retention could be improved by using lower dynamic surface tension liquids.

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4. Project Conclusions

Measurement of the characteristics of sprays in low-velocity (2 – 8 m s-1) air flows was complex due to sampling biases of droplet sizing instruments. However, evidence suggests that the changes in spray formation mechanisms, and the consequent changes in droplet size distributions, that occur because of changes in spray liquid properties are not affected by these air flows with conventional flat fan nozzles. Because of the difficulty in obtaining reliable samples with complex droplets, the effect of air flows on sprays produced by air-induction nozzles could not be evaluated. However, it is likely that similar results would have been obtained since the mechanisms of spray formation are similar to conventional flat fan nozzles.

It can be concluded, therefore, that measurements made of spray characteristics in still air with a slowly-moving nozzle will be comparable with the characteristics of sprays produced by a moving boom on a ground sprayer in the field.

The physical properties of the spray liquid have been shown to significantly influence both horizontal and vertical drift profiles measured in a wind tunnel, with increases in total airborne spray of up to 150%, compared with water alone, being measured. Although a limited number of spray liquids were tested, it is suggested that spray liquids that are emulsions are likely to reduce measures of spray drift, particularly with low drift and air induction nozzles, although this effect will be reduced if there is a significant level of surfactants present. Water-soluble formulations potentially increase drift if surfactants are present, but the degree to which this occurs depends upon nozzle design and wind speed. The correlation between percentage spray volume contained in droplets smaller than 100 m and spray drift was not good, particularly for the flat fan and hollow cone nozzles, suggesting that estimates of drift potential for different spray liquids based solely on droplet size distributions would not be accurate. Since it has been shown that the droplet size distributions produced by nozzles in wind speeds typically used for drift assessments are similar to those measured during droplet sizing in still air, it is concluded that other factors, including droplet velocities and spray structure, are important in determining drift.

The effect of spray liquid on drift depends upon nozzle design and cannot be predicted without a better understanding of the basic mechanisms. However, when making environmental risk assessments, the importance of including some information relating to spray liquid properties is crucial since the measures of drift can be increased to 270% or reduced to as low as 17% of the levels obtained when spraying with water alone.

Although some studies have shown that spray liquid has a strong influence on the quantity of spray deposited on the target plant, a much smaller effect was observed when simulating field conditions by using a canopy of outdoor-grown plants rather than individual indoor-grown pot plants. Liquid properties are most significant when retention is strongly related to the probability of a droplet being captured on first impact, and re-distribution does not occur. The effect of canopy density and plant structure will be one of the most important parameters to consider when attempting to predict distribution of spray deposits.

Air-induction nozzles gave lower levels of retention than flat fan nozzles, although this difference was largest for high dynamic surface tension liquids. This suggests that their retention could be improved by using lower dynamic surface tension liquids. The effect of nozzle type was of similar magnitude to the effect of spray liquid.

The properties of the of spray liquid, formulations and adjuvants, are important components of the spray application process. Reducing the surface tension through the additions of surfactants is likely to have a significant effect on spray drift and patterns of deposition on the crop, while having only a limited effect on the quantity deposited on target plants, particularly when the crop has formed a canopy. The use of products that form emulsions, which are common pesticide formulations, contributes to maintaining low levels of drift and potentially results in more uniform deposition patterns across a field. It must be recognised, however, that the efficacy of a product also depends strongly on spray liquid properties, and this has not been considered as part of this project.

5. References

Adams, A J; Chapple, A C; Hall, F R (1990) Droplet spectra for some agricultural fan nozzles with respect to drift and biological efficiency. In Bode, L.E, Hazen, J L, Chasin, D G (eds) Pesticide formulation and application systems ASTM STP 1078 Am. Soc for Testing and Materials, Philadelphia, 156-169

Anderson, N H, Hall, D J, Seaman, D (1987) Spray retention: effects of surfactants and plant species. Aspects of Applied Biology 14 Studies of Pesticide Transfer and Performance, 233-243

Bouse, L F; Kirk, I W; Bode, L E (1990) Effect of spray mixture on droplet size. Trans ASAE, 31 1633-1641

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Butler Ellis M C, Miller P C H, Tuck C R. (1997) The effect of some adjuvants on sprays produced by agricultural flat fan nozzles. Crop Protection 16 (1) 41-50

Butler Ellis M C, Miller P C H, Baker D E, Lane A G, Power J D, Tuck C R. (1998) The effect of LI-700 on spray formation, transport and deposition. 5th International Symposium on Adjuvants for Agrochemicals, Memphis, 17-21 August, 1998, 389-394

Butler Ellis, M.C. (1999) Report to MAFFButler Ellis M C, Tuck C R. (1999) How adjuvants influence spray formation with different hydraulic nozzles. Crop

Protection, 18, 101-110Butler Ellis M C, Tuck C R, Miller P C H. (1999) Dilute emulsions and their effect on the breakup of the liquid sheet

produced by spray nozzles. Atomization and Sprays 9 385-397 Butler Ellis, M.C.; Tuck, C.R. (2000) The variation in characteristics of air-included sprays with adjuvants. In Aspects

of Biology “Pesticide Application”, 57, 155-161Butler Ellis M C, Tuck C R, Miller P C H. (2001a) How surface tension of surfactant solutions influences the

characteristics of sprays produced by hydraulic nozzles used for pesticide application. Colloids and Interfaces A: Physicochemical and Engineering Aspects, 180 (3) 267-276.

Butler Ellis M C, Bradley A., Tuck C R. (2001b) The characteristics of sprays produced by air induction nozzles. Proceedings of the BCPC Conference - Weeds, Nov 2001, 665-670

Chapple, A C; Downer, R A, Hall, F R (1993) Effects of spray adjuvants on swath patterns and droplet spectra for a flat fan hydraulic nozzle. Crop Protection 12 579-590

Combellack JH and Richardson RG, Effect of changing droplet trajectory on collection efficiency. BCPC Monograph 28 - Application and Biology 227-233 (1985).

de Ruiter H, Uffing JMA, Meinen E and Prins A, Influence of surfactants and plant species on leaf retention of spray solutions. Weed Science 38:567-572 (1990).

Dempsey CR, Combellack JH and Richardson RG, The effect of nozzle type and 2,4-D concentration on spray collection by wheat and weeds. BCPC Monograph 28 - Application and Biology 235-240 (1985).

Durst, F; Tropea, C; Xu, T-H (1994) The slit effect in phase Doppler anemometry. In 2nd International Conference on Fluid Measurement and its Applications, 19-22 October, Bejing

Grayson BT, Price PJ and Walter D, (1996) Effect of the volume rate of application on the glasshouse performance of crop protection agent/adjuvant combinations. Pestic Sci 48:205-217.

Gyldenkaerne S, Secher BJM and Nordbo E, Ground deposit of pesticides in relation to the cereal canopy density. Pestic Sci 55:1210-1216 (1999).

Henning-Gizewski S and Wirth W, (2000) Changes in the biosynthesis of epicuticular waxes in maize and their influence on wetting properties. Pflanzenschutz-Nachrichten Bayer 53:105-125.

Hermanski, C G; Krause, G F (1995) Relevant physical property measurements for adjuvants. Proceedings of 4 th

Symposium on Adjuvants for Agrochemicals, October 1995, Melbourne, Australia, 20 –26Hewitt, A J; Sanderson, R, Huddleston, E W; Ross, J B (1994) Proceedings ILASS-Americas 94, Annual Conference

on Liquid Atomisation and Spray Systems, Bellevue, WA, 116-120Hobson P A, Miller P C H, Walklate P J, Tuck C R, Western N M. (1993) Spray drift from hydraulic spray nozzles: the

use of a computer simulation model to examine factors influencing drift. Journal of Agricultural Engineering Research, 54 293-305

Holloway, P J (1994) Physiochemical factors influencing the adjuvant-enhanced spray deposition and coverage of foliage-applied agrochemicals. In Interactions between Adjuvants, Agrochemicals and Target Organisms, Holloway, P J, Rees, R T, Stock, D (eds) Ernst Schering Research Foundation Workshop 12, Springer-Verlag, Heidelberg.

Holloway P J, Butler Ellis M C, Webb D A, Western N M, Tuck CR, Hayes A H and Miller P C H (2000) Effects of some agricultural tank-mix adjuvants on the deposition efficiency of aqueous sprays on foliage. Crop Protection 19:27-37.

Knoche, M (1994) Effect of droplet size and carrier volume on performance of foliage-applied herbicides. Crop Protection 13 163-178

Lefebvre, A H (1989) Atomization and Sprays. Hemisphere Publishing CorporationMiller, P.C.H. (1993) Spray drift and its measurement. In: Application Technology for Crop Protection (eds.

G.A.Matthews and E.C. Hislop), 102-122, CAB International, WallingfordMiller P C H, Butler Ellis M C. (1997) Spray generation, delivery to the target and how adjuvants influence the process.

Plant Protection Quarterly, 12, 1, 33-38Miller, P.C.H and Butler Ellis, M.C. (2000) Effects of Formulation on Spray Nozzle Performance for applications from

ground-based boom sprayers. Crop Protection, 19, 609-615Miller P C H, Butler Ellis M C, Gilbert A J. (2002) Extending the BCPC Spray Classification Scheme Aspects of Applied

Biology, International Advances in Pesticide Application, 66Murphy, S. D., Nicholls, T., Whybrew A., Tuck, C, R., Parkin, C. S. (2001). Classification and imaging of agricultural

sprays using a particle/droplet image analyser. Proceedings of the BCPC Conference – Weeds 2001, 677-682Richards MD, Holloway PJ and Stock D, (2000) Effects of some polymeric adjuvants on spray deposition, coverage

and dep[osit structure. Aspects Appl. Biol. 57:185-192.

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Robinson TH, Scott T, Read MA, Mills LJ, Butler Ellis MC and Lane AG, (2001) An investigation into the deposition and efficacy of pesticide sprays from air induction nozzles. BCPC Conference - Weeds 671-676.

Sanderson, R; Hewitt, E W; Huddleston, E W, Ross, J B (1997) Relative drift potential and droplet size spectra of aerially applied Propanil formulation. Crop Protection 16 717-721

Smith, R W, Miller, P C H. (1994) Drift predictions in the near nozzle region of a flat fan spray. Journal of Agricultural Engineering Research, 59, 111-120

Stevens, P J G, Kimberley, M O, Murphy, D S, Policello, G A (1993) Adhesion of spray droplets to foliage: the role of dynamic surface tension and the advantages of organosilicone surfactants. Pesticide Science 38 237-245

Teske, M E; Thistle, H W (2000) Droplet size scaling of agricultural spray material by dimensional analysis. Atomization and Sprays, 10, 147-158

Tuck, C.R., Butler Ellis, M.C., Miller, P.C.H. (1997) Techniques for measuring droplet size and velocity distributions in agricultural sprays. Crop Protection, 16, (7), 619-628

Walklate P J, Miller P C H, Gilbert A J. (2000) Drift classification of boom sprayers based on single nozzle measurements in a wind tunnel. Aspects of Applied Biology, Pesticide Application, 57 49 –56

Webb DA, (2000) Influence of some formulation ingredients and tank-mix additives on the behaviour of monosize water droplets impacting onto water-repellent foliage. BCPC Conference - Pests & Diseases 1093-1098.

Webb, D A, Parkin, C S, Andersen, P G (2002) Uniformity of the spray flux under arable boom sprayers Aspects of Applied Biology 66 87 - 94

Western N M, Hislop E C, Bieswal M, Holloway P J, Coupland D. (1999) Drift reduction and droplet size in sprays containing adjuvant oil emulsions. Pesticide Science, 55 640-642

Wirth W, Storp S and Jacobsen W, (1991)Mechanisms controlling leaf retention of agricultural spray solutions. Pesticide Sci 33:411-420.

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