effects of nozzle type and spray angle on spray deposition in ivy pot plants

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Research ArticleReceived: 23 March 2010 Revised: 15 July 2010 Accepted: 23 August 2010 Published online in Wiley Online Library: 28 October 2010

(wileyonlinelibrary.com) DOI 10.1002/ps.2051

Effects of nozzle type and spray angle on spraydeposition in ivy pot plantsDieter Foque∗ and David Nuyttens∗

Abstract

BACKGROUND: Fewer plant protection products are now authorised for use in ornamental growings. Frequent spraying withthe same product or a suboptimal technique can lead to resistance in pests and diseases. Better application techniquescould improve the sustainable use of the plant protection products still available. Spray boom systems – instead of the stillpredominantly used spray guns – might improve crop protection management in greenhouses considerably. The effect ofnozzle type, spray pressure and spray angle on spray deposition and coverage in ivy pot plants was studied, with a focus oncrop penetration and spraying the bottom side of the leaves in this dense crop.

RESULTS: The experiments showed a significant and important effect of collector position on deposition and coverage in theplant. Although spray deposition and coverage on the bottom side of the leaves are generally low, they could be improved3.0–4.9-fold using the appropriate application technique.

CONCLUSIONS: When using a spray boom in a dense crop, the nozzle choice, spray pressure and spray angle should be wellconsidered. The hollow-cone, the air-inclusion flat-fan and the standard flat-fan nozzle with an inclined spray angle performedbest because of the effect of swirling droplets, droplets with a high momentum and droplet direction respectively.c© 2010 Society of Chemical Industry

Keywords: horticulture; spray nozzle; spray boom; spray equipment; mineral chelates; crop protection; ornamentals

1 INTRODUCTIONOrnamental plants represent at least 34% of the total horticulturalproduction value in Flanders (Belgium), although they only occupy12% of the horticultural production (fruits, ornamentals andvegetables).1 In these high-value crops, 90% of the growers still usesimple high-pressure spray equipment (i.e. spray guns or lances)to apply plant protection products.

A survey among growers of ornamental plants showed thatthe growers chose the following two criteria as importantwhen choosing a spraying technique for plant protection: goodpenetration in the crop and a uniform distribution of spray liquidon the plant. These criteria are supported by the results of Barberet al.2 on spring barley, which demonstrated that uniformity of thespray on the crop was the causal factor explaining the bioefficacyof the different treatments. This survey also revealed that manygrowers are convinced that high-pressure equipment and highapplication rates (450–6650 L ha−1) are required to spray thebottom surface of the leaf. Knowing that almost all plant protectionproducts authorised for the treatment of greenhouse ornamentalplants in Belgium express the dose as a concentration (e.g. 50 g100 L−1 spray volume),3 these high application rates result in a highamount of plant protection product applied on a certain surfaceand a high potential operator exposure.4 – 7 In practice, the majorityof the growers spray until runoff (Braekman et al.).8 Information onlabels usually provides little guidance on application techniques,other than advising the operator to provide good coverage.9

Further, the usability and the optimal settings for (automated)spray boom equipment remain unclear owing to the tremendousdiversity of ornamental plants and production systems present

in Flanders.10 According to many growers, the present-day sprayapplication techniques are insufficient and need to be improved,11

although research into automatic spraying of plant protectionproducts has been addressed by several authors.12 – 18

Different studies have already demonstrated that horizontal andvertical spray booms improve spray distribution8,14,19 – 21 and/orreduce labour costs and operator exposure22,23 compared with thestill predominantly used spray guns. Derksen et al.9 concluded that,when spraying a poinsettia canopy with a single-nozzle handgunsprayer, the variability in deposition across the treatment area is acontinuing problem.

Although spray boom equipment is becoming increasinglypopular,24 many questions remain concerning the optimal settingsand nozzle choice for (automated) spray boom equipment.10

Owing to the decreasing availability of authorised plant protectionproducts, adequate pest control becomes more difficult in manyornamental crops, and almost no information is available aboutthe optimisation of spray application techniques in horizontalornamental crops. Gilles25 showed that an electrostatic reduced-volume application of permethrin insecticide to greenhouse-grown chrysanthemums resulted in significantly higher spray

∗ Correspondence to: Dieter Foque and David Nuyttens, Institute for Agriculturaland Fisheries Research (ILVO), Technology and Food Science Unit, AgriculturalEngineering, Burg. Van Gansberghelaan 115, bus 1, 9820 Merelbeke, Belgium.E-mail: [email protected]; [email protected]

Institute for Agricultural and Fisheries Research (ILVO), Technology and FoodScience Unit, Agricultural Engineering, Merelbeke, Belgium

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www.soci.org D Foque D Nuyttens

Table 1. Spray application parameters for the six application techniques selected, mean (± SE)

Techniquea Nozzle type

Sprayangle

(◦)b

Spraypressure

(bar)

Nominalflow rate(L min−1)

Measuredflow rate

(L min−1)cSpeed

(km h−1)

Applicationrate

(L ha−1)VMDd

(µm)vavg

(m s−1)e

ID Lechlerf ID 90 02 0 6.0 1.11 1.092 (±0.001) 2.86 (±0.02) 972 (±24) 402.3 (±0.2) 2.09 (±0.0)

TVI Albuzg TVI 80 02 0 6.0 1.13 1.110 (±0.006) 2.85 (±0.03) 965 (±24) 546.1 (±0.4) 1.36 (±0.0)

TXA Teejeth TXA 80 03 0 3.0 1.16 1.184 (±0.020) 2.83 (±0.04) 963 (±23) 179.2 (±0.0) 1.77 (±0.0)

XR 30◦ Teejet XR 80 03 30 3.0 1.18 1.178 (±0.003) 2.89 (±0.02) 981 (±7) 203.4 (±0.0) –

XR −30◦ Teejet XR 80 03 −30 3.0 1.18 1.178 (±0.003) 2.88 (±0.02) 978 (±11) 203.4 (±0.0) –

XR Teejet XR 80 03 0 3.0 1.18 1.178 (±0.003) 2.86 (±0.04) 984 (±16) 203.4 (±0.0) 2.45 (±0.0)

a ID: air-inclusion flat-fan nozzle; TVI: air-inclusion hollow-cone nozzle; TXA: hollow-cone nozzle; XR: extended-range flat-fan nozzle.b Spray angle relative to the movement of the spray boom: forward (30◦), downward (0◦) or back (−30◦).c Average measured flow rate of the seven selected nozzles.d Volume median diameter below which smaller droplets constitute 50% of the total volume.e One-dimensional average droplet velocity (vertical component).f Lechler GmbH, Metzingen, Germany.g Saint-Gobain Solcera, Evreux Cedex, France.h TeeJet Technologies, Wheaton, IL.

deposition compared with conventional high-volume application.However, this technique also resulted in significantly highercontamination of non-target surfaces of the greenhouse benchtops and aisle ways.

The importance of the application technique, and morespecifically the effect of spray quality and volume, on the controlof pests in open field crops has been highlighted in several studiesin different crops including soybean,26 – 28 onion,29 canola,30

cereals,2,31 – 33 peanut,34 potatoes35 and cotton.36 Other studiessuggest that spray quality and pressure are not so important withregard to deposition and disease control,37 – 40 and that coarse-droplet applications are able to produce equal results in terms ofbiological efficacy.41 – 45

The effect of spray angle has been studied in only a limitednumber of open field crops. An increased deposition was observedwith angled sprayings in ryegrass46,47 and cereals.47,48 In cereals,a decrease in spray losses to the soil was found with angledspray applications.49 Jensen50 found that angling the spray eitherforward or back relative to the direction of travel increasedherbicide efficacy. Moreover, efficacy generally increased withincreasing angle to vertically down, and a forward-angled sprayimproved efficacy most. Womac et al.36 found that orienting the airstream of an air-assisted sprayer 30◦ back increased deposits on theleaf underside. On the other hand, Zhu et al.34 demonstrated thatinclining a single flat-fan nozzle 15◦ forward did not improve spraypenetration in a peanut canopy, and Derksen et al.51 reported thatspray deposits were similar for a 60◦ twin flat-fan nozzle comparedwith standard nozzles on bell peppers.

In this study, the potential effect of nozzle type, spray pressure,droplet characteristics and spray angle on spraying of the bottomsurface of the leaf, the penetration of the spray liquid and theuniformity of liquid distribution on the crop was studied in ivy potplants (Hedera algeriensis Hort. cv. Montgomery) under laboratoryconditions.

2 MATERIALS AND METHODS2.1 Spray application techniquesA self-propelled aluminium frame was constructed in order to usea horizontal spray boom at different heights. Four nozzle types,set at six different nozzle settings (Table 1), were evaluated, i.e. a

TeeJet TXA 80 03 hollow-cone nozzle, a TeeJet XR 80 03 extended-range flat-fan nozzle, an Albuz TVI 80 02 air-inclusion hollow-conenozzle and a Lechler ID 90 02 air-inclusion flat-fan nozzle.All nozzles were tested when spraying vertically downwards.Additionally, the TeeJet XR 80 03 nozzle was tested when angledforward (+30◦) and back (−30◦). Applications were made at therecommended working pressure, which varied from 3.0 to 6.0 bardepending on the type of nozzle, with an average driving speedof 2.86 ± 0.01 km h−1 (mean ± SE). This resulted in an applicationvolume of about 1000 L ha−1 (Table 1), which is the minimumvolume often suggested by manufacturers of plant protectionproducts used on ornamental crops kept in greenhouse conditions.

2.1.1 Droplet characteristicsDroplet size and velocity characteristics at 0.50 m below the nozzle(Table 1) were obtained using a PDPA laser-based measuringset-up52,53 because of their importance with regard to cropcoverage,54 – 56 spray drift risk57 – 60 and biological efficacy.38,45,61

2.1.2 Spray boom set-upBecause of the growers’ need to work in narrow spaces, boomconfigurations as used on land are not suitable for greenhouses.Knewitz et al.62 proved that a reduced interspacing of 0.155 mbetween nozzles and a nozzle height of 0.2 m above the canopyare adequate for greenhouse spraying. In the present study,however, a reduced nozzle distance of 0.25 m was selected fortwo reasons. First, the larger interspacing considerably reducesthe number of nozzles required. Second, this distance betweennozzles ensures that existing sprayers, which are mostly designedfor agriculture, can be easily adapted to conform to the findings ofthese experiments. Based on previous tests,20,62,63 nozzles with asmaller spray angle were selected (Table 1) (usually 80◦, except forthe Lechler ID 90 02 air-inclusion flat fan) to minimise spray losseswhile maintaining sufficient overlap. Spray boom width was 1.5 m.

2.1.3 Spray boom distributionTo ensure a correct spray application rate and a uniform sprayboom distribution, the flow rate of ten nozzles of four differentnozzle types (Table 1) was measured according to the ISO standard5682-1.64

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Effects of nozzle type and spray angle on spray deposition in ivy pot plants www.soci.org

To determine the optimum boom height during the exper-iments, spray distribution measurements were done with adistribution bench (ISO 5682-1) with the same nozzle types atboom heights of 0.25, 0.35 and 0.45 m to calculate the coefficientof variation (CV). Flow rate and distribution measurements wereperformed in the ILVO Spray Tech Lab under BELAC accreditation.65

2.2 Experimental set-up and crop characteristicsIvy pot plants (H. algeriensis cv. Montgomery) were used to evaluatethe effect of the six selected application techniques (Table 1) oncrop deposition and coverage. The plants were placed on arolling bench (2.00 m × 3.50 m) in three rows of six plant pallets(0.53 m × 0.31 m), as presented in Figs 1 and 2. The rolling benchwas positioned with its longest side parallel to the direction ofmovement of the spray boom.

Each pallet contained six ivy pot plants. Plant density was 32.6plants m−2. Because of the design of the tray, plant distanceswere about 16, 19 and 21.5 cm, respectively, for the plant distancewithin the same pallet in the spray direction, the plant distanceperpendicular to the spray direction and the distance betweenthe first and the last plant of two consecutive pallets in the spraydirection (Fig. 1). The plant characteristics and set-up resulted in aclosed and dense canopy with an average height of 19.6 ± 3.1 cm.

For each spraying, filter paper collectors (FPCs) were attachedto 20 collector plants, and water-sensitive papers (WSPs) to sixcollector plants using small paper clips (Figs 1 and 2). For eachplant, six collectors were equally distributed between three cropzones on leaves with a size at least the collector size. Two collectorswere positioned in the upper layer at an average height of19.9 ± 2.7 cm. Two other collectors were placed in the middlelayer on leaves at an average height of 9.0 ± 2.8 cm above thepot. In both crop zones, one collector was on the upper surfaceof a leaf and one on the bottom surface of another leaf. The tworemaining collectors were placed at the bottom of the plants. Onewas placed on top of a small petri dish, horizontally to the soil,while the other was attached vertically to the plant’s stem withouttouching the soil. The latter two collectors gave an indication ofcrop penetration and possible differences in runoff. Each collector’sheight was measured during the experimental set-up. The collectorplants were randomly distributed between the other ivy plants.

To measure off-target spray deposition, six filter paper collectorswere placed within 0.225 m of the crop’s edge, and six others withinthe crop between the pots (Fig. 1).

Each spray application was repeated 3 times. While the WSPswere replaced for every spraying, the same filter paper collectorswere used for every set of six different application techniquesusing a different mineral chelate (Chelal; BMS Micro-NutrientsNV, Bornem, Belgium) in a randomised order to obtain a directcomparison between the different techniques. After each set ofsix applications, all plants were replaced. FPCs and WSPs werestored in marked and sealed jars and kept dry pending furtherprocessing, as discussed below.

After collecting, the crop’s layout was taken apart and built upagain, plant by plant. The location of the collector plants and theoff-target positions within the crop were selected randomly witheach subsequent repetition to exclude possible influences of thecrop’s layout and the positioning of the collector plants and theoff-target positions.

Plant architecture characteristics (e.g. mean leaf angle andmean diameter of plants) were measured using a ruler, goniometerand level, and the leaf area index (LAI) was measured at the top,middle and bottom of the ivy canopy using the Sunscan canopy

Figure 1. Layout of a typical experimental set-up with 20 plants with filterpaper collectors (1–20), six plants with water-sensitive paper collectors(1–6) and 12 off-target collectors [0.225 m from the crop’s edge: 1–6(OTout); within the crop: 1–6 (OTin)].

analysis system (SS–TM-1.05; Delta-T Devices Limited, Cambridge,UK). At the top layer, the sensor area was only covered by the firstleaf of the foliage.

2.3 Spray depositionSpray deposition (distribution and penetration) in the canopywas evaluated by the mineral chelate tracer method8,20,21,23 usingFe, Co, Cu, Mn, Mo and Zn chelates at a targeted concentrationof 1.0 g L−1. For each spray application technique, a differentmineral chelate was used. These products are normally used as

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Figure 2. Picture of one collector plant (left) and the layout of a typical experimental set-up (right).

Table 2. Coefficients of variation for three different heights for the width of the spray boom (A) and the actual spray width (B)

TXA 80 03 XR 80 03 TVI 80 02 ID 90 02

Spray boom height (m)

0.25 0.35 0.45 0.25 0.35 0.45 0.25 0.35 0.45 0.25 0.35 0.45

CV (%) A 20.2 13.2 11.2 5.7 7.2 8.9 37.4 27.3 8.2 6.9 8.5 8.4

B 21.2 17.4 16.5 9.4 10.8 13.7 37.6 31.0 15.8 10.6 12.4 12.6

A = CV underneath the width of the spray boom (1.50 m).B = CV within the actual spray width (1.75 m).

horticultural leaf fertilisers and perform as pesticides under thesame conditions. The reliability of this method has already beenconfirmed by other authors.66 – 71

Filter paper collectors (5.7 cm × 2.6 cm; Schleicher & Schuell,type 751, Filter Service NV, Eupen, Belgium) were distributedover the three crop zones of the 60 sample plants as describedabove. The crop and collectors were allowed to dry completelybetween two successive sprayings. Drying time ranged from 2 to4 h, depending on ambient conditions. After spraying with all sixtechniques, FPCs were gathered and analysed using inductivelycoupled plasma (ICP) analysis (VISTA-PRO; Varian, Palo Alto, CA).8,21

Every repetition had 120 plant collectors, 12 off-target collectors,24 tank samples and eight blanks. This resulted in a total number of2376 deposition measurements, corresponding to 396 collectors(132 collectors × 3 repetitions).

The spray deposition (L ha−1) on every collector was calculated,with the actual concentration in the tank, the calculatedapplication rate, the quantity of 0.16 M nitric acid (66+%, proanalysis; Acros Organics, Geel, Belgium) used for extraction andthe analysis of the blank samples taken into account. For acomparative assessment of the different techniques, the resultswere normalised to an application rate of 1000 L ha−1 and a tankconcentration of 1.0 g L−1.

2.4 Spray coverageSpray coverage at the different positions in the crop was assessedusing water-sensitive papers. WSPs have been used in manystudies as a tool for quickly providing a cheap evaluation ofspray coverage.72 – 74 For each spraying, six plants were equippedwith six WSPs (2.6 × 3.8 cm; Syngenta Crop Protection AG, Basel,Switzerland) over the three crop zones, as described in Section2.2, which resulted in 648 spray coverage measurements. Aftereach spraying and complete drying, the WSPs were gathered and

digitised at 600 dpi. All sprayings were done at a low relativehumidity (42 ± 7%) to prevent the WSP from turning blue becauseof high relative humidity. An image analysis system developed byJeroen Baert using Halcon 8.0 software (MVTec Software GmbH,Munich, Germany) was used to calculate spray coverage of thedifferent collectors.

2.5 Statistical analysisStatistica 7.1 (Statsoft Inc., Tulsa, OK) was used for all statisticalanalysis. A P-value of <0.05 was considered to be statisticallysignificant.

Because travelling speed (Shapiro–Wilk’s test: W = 0.93,P = 0.16) and application rate (W = 0.95, P = 0.41) provedto be normally distributed, one-way ANOVA could be used tocompare spraying parameters between nozzles and repetitions.

No adequate way to transform the deposition results (W = 0.64,P < 0.05) into a normally distributed dataset was found. For thisreason, non-parametrical Kruskal–Wallis tests were used to analysedeposition data. The effect of the different application techniqueswas tested for the different collector positions.

3 RESULTS3.1 Nozzle flow rates and spray boom liquid distributionSeven out of ten nozzles per type were selected, based on thedeviation of their measured flow rate from the nominal flow rate.Average measured flow rates are presented in Table 1. Deviationof these values from the corresponding nominal flow rate was verylimited and ranged from −1.8 to 2.1%.

Table 2 presents the measured coefficients of variation (CV)at three heights. An overall optimal boom height of 0.45 m wasfound. This height resulted in the smallest set of coefficients ofvariation between all nozzle types. For a boom width of 1.5 m, CV


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Figure 3. Spray deposition (L ha−1) at different collector positions (mean ± SE) with a natural (A) and a logarithmic (B) scale of the Y-axis. 1: upper layer,upper side of leaves; 2: upper layer, bottom side of leaves; 3: middle layer, upper side of leaves; 4: middle layer, bottom side of leaves; 5: ground level,attached to stem; 6: ground level, horizontal to soil. Bars carrying the same label are not statistically different.

values of 11.2, 8.9, 8.2 and 8.4% were found, respectively, for theTeeJet TXA 80 03, the TeeJet XR 80 03, the Albuz TVI 80 02 and theLechler ID 90 02 nozzles. These values fulfil the European standardEN 12 761-2 for standard flat-fan nozzles (CV<9%),75 except for theTeeJet TXA hollow-cone nozzles. A boom height of 0.45 m abovethe canopy was maintained throughout all spray experiments.

3.2 Spray depositionApplication rate and speed of the spray boom as observed duringspraying (Table 1) were statistically analysed to prove similaritiesbetween repetitions and nozzle types. Statistical differenceswere only found when comparing repetitions (F2,15 = 5.43,P = 0.017). Because these differences are not reflected insignificant differences for application rate, all nozzle types couldbe compared without any restrictions.

For each of the six collector locations (numbered 1 to 6 below),spray depositions for the different techniques are shown in Fig. 3(mean ± SE). These collector numbers refer to a specific collectorposition as follows: 1: upper layer, upper side of leaves; 2: upperlayer, bottom side of leaves; 3: middle layer, upper side of leaves;4: middle layer, bottom side of leaves; 5: ground level, attached tostem; 6: ground level, horizontal to soil.

The effect of the different application techniques was evaluatedusing Kruskal–Wallis tests. Significant differences were found atmost collector positions. The results of this analysis are shown inFig. 3.

The off-target depositions were evaluated as above. Off-targetpositions between plant pots (OTin) were found to capture asignificantly lower amount of spraying liquid [H (2, N = 222) =157.36, P < 0.05] than collectors placed outside the crop (OTout).


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Figure 4. Spray coverage (%) at different collector positions (mean ± SE) with a natural (A) and a logarithmic (B) scale of the Y-axis. 1: upper layer, upperside of leaves; 2: upper layer, bottom side of leaves; 3: middle layer, upper side of leaves; 4: middle layer, bottom side of leaves; 5: ground level, attachedto stem; 6: ground level, horizontal to soil. Bars carrying the same label are not statistically different.

No other significant differences could be found using statisticaltechniques. Mean depositions of 210 ± 6 L ha−1 for OTout [H (5,N = 102) = 9.990762, P = 0.08] and 40 ± 3 L ha−1 for OTin [H (5,N = 108) = 3.30, P = 0.65] were found.

3.3 Spray coverageSpray coverage results (%) for the different locations (numbered1 to 6 below) and techniques are presented in Fig. 4 (mean± SE). The effect of the different application techniques wasagain evaluated using Kruskal–Wallis tests. Significant differenceswere found at most collector positions. In general, there is agood correspondence between spray deposition and coverageresults.

3.4 Crop characteristicsA total of 59 leaf angles were measured, resulting in a mean leafangle of −7.4 ± 4.2◦ relative to the horizontal. The mean diameterof the ivy pot plant was determined by averaging the diameterof five different plants, measured in three different directions.These 15 measurements resulted in an average plant diameter of32.7 ± 2.2 cm. The LAI increased from top to bottom: it measured2.1 at the top, 5.5 in the middle and 6.9 at the bottom of the plants,corresponding to average heights of about 19.9, 9.0 and 3.4 cmabove the pot.

Considering these plant characteristics together with thosepresented in the discussion of the experimental set-up, the ivycrop can be described as a dense canopy with many shielded


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features caused by frequently overlapping foliage from differentplants and the more or less horizontal position of the leaves.

4 DISCUSSIONThe experiments showed a significant and important effect ofsampling position on deposition and coverage. Highest valueswere found in the upper layer on the upper side of the leaves(from 225 to 317 L ha−1, from 58 to 79% coverage), followed bythe middle layer on the upper side of the leaves (from 55 to 108 Lha−1, from 21 to 32% coverage) and the ground level, horizontalto the soil (from 18 to 32 L ha−1, from 9 to 18% coverage). Lowestcoverage and deposition were measured on the bottom side of theleaves in the middle layer, ranging from 0.2 to 0.8% and from 0.5to 2.4 L ha−1, which corresponds to 0.05–0.2% of the applicationrate.

On the bottom side of the leaves in the upper layer, valuesvaried from 9.9 to 30.0 L ha−1 and from 0.7 to 3.3%. Depositionand coverage on the collector attached to the stem were ofthe same order of magnitude, from 6.7 to 15.6 L ha−1 and from2.0 to 6.1% respectively. The variation in 3D plant architecture,spray distribution and positioning of the collectors explains thevariability of the deposits measured at each sample point for thesame application technique, as indicated by the error bars in Fig. 3.

Besides sampling position, the spray application techniqueaffected spray deposition and coverage. Deposition on the upperside of the leaves was lowest in the upper leaf layer (position 1in Figs 3 and 4) when using XR 80 03 nozzles at an inclined sprayangle (30◦ and −30◦). Spraying with the XR 80 03 nozzles at theseinclined spray angles led to depositions comparable with thoseobtained with the TVI 80 02 nozzles (TVI). Moreover, no statisticallysignificant difference could be found between the XR 80 03 (−30◦)(XR −30◦) on the one hand and the XR 80 03 nozzle when usedwith a normal spray angle (XR). In spite of its worst CV, the TXA 8003 nozzle (TXA) gave the highest average deposits within this plantlayer, but could not be statistically distinguished from the resultsof the ID 90 02 (ID), the TVI and the XR nozzles. In acccordance withdeposition results, spray coverage was highest for the TXA nozzle(79%), followed by the XR −30◦ nozzle (70%). Spray coveragewith the TXA nozzle was significantly higher than the ID, TVI,XR 30◦ and XR applications. Differences between deposition andcoverage results can mainly be attributed to droplet size effectsbecause, for the same spray deposition, nozzles with smallerdroplet spectra produce the highest coverage.76 For example, forthe TXA and ID nozzles, comparable deposition results were found,while coverage was significantly higher for the TXA nozzles. Ingeneral, spray deposition and coverage are high on the upper leafsurface in the top layer, and potentially high enough for adequatepest control in this plant zone irrespective of spray applicationtechnique. There is a 1.4-fold difference in spray deposition andcoverage between the worst and the best application technique.

For deposition on the upper side of the leaves in the middlelayer of the canopy (position 3), the ID, the TXA and the XR nozzlesproduced the highest deposits. The depositions of the TXA andXR nozzles, however, were statistically similar to those of theother application techniques because of the important variationin spray deposits, as indicated by the error bars in Fig. 3. For thesame reason, there were no statistically significant differences inspray coverage values, although similar trends were found. Atthis position, the effect of application technique becomes moreimportant, as there is a twofold difference in mean spray deposition

and a 1.5-fold difference in mean spray coverage between bestand worst technique.

On the bottom side of the leaves in the upper layer (position2), spray deposits were statistically lowest for the TVI nozzle, andspray coverage for the TXA nozzle. At this position, the XR 30◦

produced the highest deposition as well as coverage. However,the deposits of the XR 30◦ nozzle configuration are not statisticallydifferent from those of other application techniques because ofthe considerable variation in measuring results, except for thedeposit values of the TVI nozzle and the coverage values of theTXA nozzle.

Looking to the spray deposits in the middle layer of the crop onthe bottom side of the leaves (position 4), the ID and TXA nozzlesscored well, although use of the TXA nozzle resulted in statisticallysimilar results to those recorded with the XR 30◦ and XR −30◦

nozzle configurations. The deposition of these inclined nozzleconfigurations could not be distinguished from those of the TVIand the XR nozzles, which were the lower-scoring group of nozzlesin position 4. As regards spray coverage, highest values were foundfor the ID and the XR 30◦ and XR −30◦ nozzle configurations.

Considering the bottom sides of the leaves, there is a threefold(upper layer) and 4.9-fold (middle layer) difference in depositionand a 4.9-fold (upper layer) and 4.1-fold (middle layer) difference incoverage between the best and the worst application technique.This demonstrates the important effect of application technique,although the deposition on the bottom surface of the leaves is stilllow for the different techniques because of the effect of shielding.Turner and Matthews63 also reported low coverage on the bottomsurface of leaves from several types of hydraulic nozzle. However,as several growers emphasised the importance of reaching thelower side of the leaves, even the limited improvement mainlyobtained with the ID and the inclined XR nozzles could lead toimproved biological efficacy.

The XR 30◦ nozzle also produced the highest deposition andthe XR −30◦ the highest coverage on the collector at ground levelattached to the stem (position 5), which again proves an improvedpenetration capacity. This deposition might be the result of directdeposition as well as from runoff down to the stem.

Results of positions 2 and 4 show that the TXA, ID, XR 30◦ andXR −30◦ nozzles generally gave the highest depositions on thebottom side of the leaves. For the TXA hollow-cone nozzle, this iscaused by the swirling effect created by the swirl insert, resulting insmall droplets swirling between the leaves.63,77 In spite of the gooddeposit values of this nozzle type, the coverage values were low.The ID nozzle produces the coarsest droplet size spectrum [volumemedian diameter (VMD) = 402.3 µm] (Table 1) in combinationwith a high average vertical droplet speed (2.09 m s−1), resulting ina high momentum and capacity to penetrate the crop canopy.21,78

Although there is sometimes a concern that because of the largerdroplets a reduction in efficacy may occur,31 different studiesdemonstrated that air-injection nozzles provide at least a similarperformance to conventional sprays.41 – 45 For the XR nozzle, theinclined spray angle had a positive effect on penetration, spraydeposition and coverage on the bottom side of the leaves, which isin agreement with previous studies.46 – 48 For example, at position4, the XR nozzle with an angle of 30◦ or −30◦ led to depositionsstatistically equal to those of the TXA nozzle, while that was nottrue for the XR nozzle.

Based on the statistical analysis of the deposition results at thebase of each plant (position 6), application techniques could bedivided into three groups. The highest depositions came from thegroup consisting of the TXA nozzles, because of the swirling effect,


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and the ID nozzles, because of their high droplet momentum. Forthe ID nozzles, there might be an additional effect of runoff ofthe big droplets. The low-scoring group included only one nozzle,namely the TVI. These two groups are not significantly differentfrom the nozzle types in the third group, which comprises the XRnozzles used with the three different spray angles. Spray depositsmeasured at position 6 are in the same range as the off-targetdeposition between plants pots (OTin), indicating that, in spite ofthe dense crop, a considerable amount of pesticide is lost to theground as well as to the non-target zone outside the crop (OTout).At position 6, no significant differences in spray coverage valueswere found.

Overall, the hollow-cone (TXA 80 03), the standard flat-fan (XR80 03, 0◦, 30◦ and −30◦) and the air-inclusion flat-fan (ID 9002) nozzle configurations performed best, which is confirmedby studies of Braekman et al.21 for the ID and XR nozzle andTurner and Matthews63 for the TXA nozzle. When deposition isviewed from the top to the bottom of the plants, the ID and TXAnozzles always lead to comparable results with the best-scoringapplication technique. The TXA 80 03 nozzle should preferablybe used only for indoor applications because of its small dropletsize (Table 1) and high driftability.52,59 Using the XR nozzles withan inclined spray angle had a positive effect on penetration anddeposition on the bottom side of the leaves.

The findings of this study could not unambiguously be linked tothe ISO size of the nozzle, the pressure used for sprayings, the VMD,the droplet velocity or the nozzle type. It might be assumed thatdifferences between application techniques are masked becauseof the high spray volume of 1000 L ha−1, as confirmed by Braekmanet al.8 In future, the effect of spray angle in combination with airsupport79 – 82 and spray volume will be investigated to improvecrop penetration and deposition further, and bioefficacy trials willbe carried out to link deposition results with the bioefficacy ofnon-systemic plant protection products.

ACKNOWLEDGEMENTSThe authors would like to thank the Flemish Government – IWTVlaanderen – for financial support. They would also like toacknowledge the Research Centre for Ornamental Plants (PCS)and members of ILVO’s technical staff – especially Olav VanMalderen – for their assistance during the experiments. Specialthanks go to Miriam Levenson for thoroughly reviewing thispaper, and to Jeroen Baert for helping with the image analysis.

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