Effect of spray application technique on spray deposition in greenhouse strawberries and tomatoes

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Research ArticleReceived: 24 April 2009 Revised: 16 July 2009 Accepted: 16 July 2009 Published online in Wiley Interscience: 15 October 2009

(www.interscience.wiley.com) DOI 10.1002/ps.1858

Effect of spray application technique on spraydeposition in greenhouse strawberries andtomatoesPascal Braekman,a Dieter Foque,a Winy Messens,b

Marie-Christine Van Labeke,c Jan G Pietersd and David Nuyttensa∗

Abstract

BACKGROUND: Increasingly, Flemish greenhouse growers are using spray booms instead of spray guns to apply plant protectionproducts. Although the advantages of spray booms are well known, growers still have many questions concerning nozzle choiceand settings. Spray deposition using a vertical spray boom in tomatoes and strawberries was compared with reference sprayequipment. Five different settings of nozzle type, size and pressure were tested with the spray boom.

RESULTS: In general, the standard vertical spray boom performed better than the reference spray equipment in strawberries(spray gun) and in tomatoes (air-assisted sprayer). Nozzle type and settings significantly affected spray deposition and croppenetration. Highest overall deposits in strawberries were achieved using air-inclusion or extended-range nozzles. In tomatoes,the extended-range nozzles and the twin air-inclusion nozzles performed best. Using smaller-size extended-range nozzlesabove the recommended pressure range resulted in lower deposits, especially inside the crop canopy.

CONCLUSIONS: The use of a vertical spray boom is a promising technique for applying plant protection products in a safe andefficient way in tomatoes and strawberries, and nozzle choice and setting should be carefully considered.c© 2009 Society of Chemical Industry

Keywords: horticulture; spray nozzle; vertical spray boom; spray equipment; mineral chelates; crop protection; air support

1 INTRODUCTIONIn Flanders, the northern region of Belgium, almost 8% of thearable land is used for horticultural plant production (fruits,ornamentals and vegetables), representing a value of ¤1.33 billionin 2005. This accounts for 30% of the total agricultural andhorticultural production value in Flanders. Glasshouses occupyapproximately 4.3% of the horticultural area.1 Tomatoes are themost important vegetable grown in Flemish glasshouses, with46% of the cropped area, while strawberries cover approximately86% of the glasshouse area dedicated to fruit production.2 Inthe past, mainly spray guns were used for spraying, mostly at ahigher pressure than recommended, but spray boom equipmentis now becoming increasingly popular among growers.3 In spiteof important advantages, e.g. a more uniform spray liquiddistribution, many questions remain concerning the optimalsettings for this type of equipment.4 Furthermore, a surveycarried out in 2007 among growers of ornamental plants, whouse comparable greenhouse production systems, revealed thatthe present-day spray application techniques are insufficient andneed to be improved.5 Information on labels usually provideslittle guidance on application techniques, other than advising theoperator to provide good coverage.6

It is generally accepted that the foliar application of a pesticideto a crop is in fact a very inefficient process, with only a fractionof the pesticide actually being retained on plants and some beinglost to the ground.7 The amount retained on the crop depends on

many factors, including the formulation of pesticide used,8 – 10 theweather conditions,11 – 13 the volume of spray applied,6,14 the typeof spray equipment15 – 17 and the spray quality.6,15

According to Cho and Ki,18 30–35% of production losses canbe saved when harmful insects and diseases are controlled byspraying. The importance of the application technique to controlpests or diseases in both strawberries and tomatoes grown inglasshouses has been highlighted in several studies. Tanigawaet al.19 reported an inadequate deposit of fungicide on thelower leaf surface of several strawberry cultivars for control

∗ Correspondence to: David Nuyttens, Institute for Agricultural and FisheriesResearch (ILVO), Technology and Food Sciences Unit, Agricultural Engi-neering, Burg. Van Gansberghelaan 115, bus 1, 9820 Merelbeke, Belgium.E-mail: [email protected]

a Institute for Agricultural and Fisheries Research (ILVO), Technology and FoodSciences Unit, Agricultural Engineering, Burg. Van Gansberghelaan 115, bus 1,9820 Merelbeke, Belgium

b Institute for Agricultural and Fisheries Research (ILVO), Technology and FoodSciences Unit, Food Safety, Brusselsesteenweg 370, 9090 Melle, Belgium

c Ghent University, Department of Plant Production, Coupure Links 653, 9000Ghent, Belgium

d Ghent University, Department of Biosystems Engineering, Coupure Links 653,9000 Ghent, Belgium

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of powdery mildew when swinging a nozzle pendulously overthe crop. Bjugstad and Sønsteby20 considered that 80◦ flat-fannozzles at a distance of 200 mm from the plants was the bestpractical method for spraying an outdoor strawberry. For smallerand larger plants, three ISO 03 nozzles and five ISO 02 nozzlesachieved the highest deposition and coverage score respectively.Also, in outdoor cropped strawberries, Vandemersch et al.21 foundthat, irrespective of the application techniques used, depositionwas often poor, indicating that all applications needed to beoptimised. They assumed that air induction nozzles could improvethe spraying.

In tomatoes, Nuyttens et al.22 demonstrated that simplyreducing the vertical nozzle spacing between nozzles from 0.50to 0.35 m on vertical spray booms was a simple and cheapadaptation to improve spray distribution in tomatoes as wellas in peppers. Derksen et al.23 showed that coverage of tomatoesvaried significantly more between nozzles and machines than didoverall spray deposits. High-pressure sprays did not penetratethe canopy or improve coverage better than low-pressure sprays.Furthermore, significant coverage on the undersides of leavesrequired air-assisted spraying. Abdelbagi and Adams15 reportedthat a rotary atomiser delivering charged sprays in tomatoes wasmost effective in areas where the canopy did not interfere withspray movement. However, Lee et al.24 obtained an improveduniformity on upper and lower tomato leaf surfaces using flat-fan nozzles directed upwards at 45◦ or with air-assisted systemsapplying 400–500 L ha−1. Tunstall et al.25 also used vertical spraybooms with narrow-angle cone nozzles directed 45◦ upwardsto provide better penetration and to improve the undersurfacecoverage of leaves in cotton crops. van Os et al.26 found that aspray pressure ranging from 5 to 10 bar in tomatoes providedoptimal depositions and considerably reduced chemical losses,while Sanchez-Hermosilla et al.27 showed that spray depositionapplying 750 L ha−1 with a vertical boom sprayer at 15 bar ontomato plants was comparable with that using a gun sprayer at2000 L ha−1 applied at 38 bar.

Another important factor when treating plants with a handheldgun sprayer in greenhouses is that potential operator exposureis high.28 – 32 However, the use of vertical spray booms greatlydecreases operator exposure and increases productivity.27,33,34 Forthese reasons, research into automatic spraying of plant protectionproducts has been addressed by several authors.18,35 – 39

The main objective of this research was to investigate theeffect of spray application technique on the spray deposition instrawberries and tomatoes grown in greenhouses to assess theeffect of nozzle type, size and spray pressure and how verticalspray booms compare with the reference spray equipment.

2 MATERIALS AND METHODS2.1 Spray equipmentA preliminary inquiry among strawberry and tomato growersrevealed that, on average, a spray volume of 1000 L ha−1 ofgreenhouse area is applied in both crops. Using spray booms, thedriving speed for strawberries is approximately 3.6 and 2.9 kmh−1 in tomatoes. Nozzle sizes and their configuration on the sprayboom were carefully chosen to meet these mean spray parametersin both experiments. The current recommended practice is tospray at moderate pressures (500–600 kPa for strawberries and600–700 kPa for tomatoes), but most growers take no notice ofthis when using standard or extended-range flat-fan nozzles witheither 80◦ or 110◦ spray angle on their spray booms. To guaranteemaximal overlap and uniform spray liquid distribution, flat-fannozzles with a 110◦ or 120◦ spray angle were used (Table 1),with the distances between nozzles reduced on the verticalspray booms as suggested by Nuyttens et al.22 Using a PDPAlaser-based measuring set-up and protocol,40 the volume mediandiameter and the one-dimensional (i.e. perpendicular to the sprayboom) volumetric average droplet speed for the nozzle–pressurecombinations used on the spray booms were measured at 0.50 mfrom the nozzle (Table 1). Within the spray equipment system,droplet size and velocity characteristics41,42 are the most influential

Table 1. Spray application parameters for the 12 different trials

Crop Spraying equipment Nozzle type

Travellingspeed

(km h−1)

Spraypressure

(kPa)

Applicationrate

(L ha−1) Mineral chelateVMDd

(µm)vvol50

e

(m s−1)

Strawberriesa Vertical boom TeeJet XR 11003 1.99 250 898 Iron 212.5 6.37

TeeJet DG 11003 2.16 250 807 Molybdenum 286.9 6.80

TeeJet XR 11002 2.06 600 880 Manganese 187.0 8.77

Lechler ID 12002 2.03 600 833 Zinc 373.7 8.89

Albuz AVI-Twin 11002 2.06 600 819 Cobalt 184.0 1.26

Spray gun TeeJet D 1.5 1.72 1000c 1457 Copper – –

Tomatoesb Vertical boom TeeJet XR 11003 1.41 350 989 Zinc 205.6 6.66

TeeJet DG 11003 1.30 350 1071 Copper 278.9 6.89

TeeJet XR 11002 1.39 700 1006 Cobalt 191.8 9.73

Albuz ATR orange 1.39 830 1001 Manganese 82.7 1.44

Albuz AVI-Twin 11002 1.33 800 1063 Iron 181.3 1.48

Air-assistance spouts Flat-fan 80015 1.46 640 1223 Molybdenum – –

a ∼6250 running metres of plants per hectare.b ∼8300 running metres of plants per hectare.c Pressure at the pump.d Volume median diameter below which smaller droplets constitute 50% of the total volume.e One-dimensional droplet velocity (vertical component) below which slower droplets constitute 50% of the total spray volume.

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factors and are important for crop coverage,43 – 45 spray driftrisk13,46 – 48 and the biological efficacy of the applied pesticide.49,50

In strawberries, six spray application techniques were tested(Table 1), including the traditional spray gun equipped with threedifferently oriented disc-core nozzles. The spray gun was fed by a100 m long hose [diameter 3/4′′ (19 mm)]. During the experiments,the hose was only half unrolled from the drum. No pressure gaugewas present at the spray gun, so pressure was set on the gaugemounted on the pump. During the sprayings, the spray gun washeld at a constant height of about 1.60 m above the ground and aconstant distance of about 0.30 m from the crop canopy. The fiveother spray application techniques tested in strawberries madeuse of a self-propelled sprayer fitted with a standard vertical sprayboom (Fig. 1A and Table 1). Three nozzles of the same type andsize were fitted on the boom 0.20 or 0.25 m apart with an offsetangle of 7◦ so that they were 1.475, 1.675 and 1.925 m above thesoil surface. The lowest and middle nozzles were oriented directlytowards the crop canopy, whereas the top nozzle was slightlyinclined (15◦) downwards.

For the trials in tomatoes, six spray application techniques wereused on a semi-automated trolley sprayer that moved along theheating pipes as presented in Table 1. The first technique consistedof two sets of three air-assisted spouts, one set at each side of thesprayer (Fig. 1B). All spouts were fitted with an 80◦ ISO 015 flat-fan nozzle oriented 45◦ upwards and 30◦ backwards. The nozzleswere 1.285, 1.565 and 1.845 m above the heating pipes, i.e. at thestandard setting used by the grower. An engine drives the spraypump and fan, but the sprayer has to be pulled manually duringspraying. For the five other techniques, the air-assisted spoutswere removed and replaced with a standard vertical spray boom(Fig. 1B) fitted with three nozzles (Table 1) spaced 0.25 m apart sothey were 1.40, 1.65 and 1.90 m above the heating pipes with anoffset angle of 7◦. No air assistance was used for these sprayersettings.

The spray gun and the sprayer equipped with air-assistedspouts were considered as the reference spray equipment forstrawberries and tomatoes respectively. All sprayings were carriedout by experienced growers.

2.2 Experimental set-upThe experiments were conducted in two greenhouses in October2007 and involved a randomly selected row of either strawberries(approximately 8300 running metres ha−1) or tomatoes (approxi-mately 6250 running metres ha−1). The varieties used were Elsanta(strawberry) and Tradero (tomato). The strawberry crop had an av-erage height of 0.40 m and its growth stage could be describedas ‘end of fruit production’, but the runners had not yet beenremoved. The tomato crop was also at an advanced growth stage(plant apex removed, flowering of last raceme). In the experiments,the sprays were targeted at a zone of about 1 m height comprisingthe tomato fruits (Fig. 1B).

In all experiments, nozzle size and spray pressure were selectedto spray a volume of 1000 L ha−1 at fixed travel speeds, 3.6 kmh−1 in strawberries and 2.9 km h−1 in tomatoes. The actual travelspeeds and spray pressures were measured to calculate the exactapplication rates (Table 1). In the strawberry crop, the averagespray distance was 0.35 m,22 measured between nozzle orificeand the crop contours. The average spray distance to the outertomato leaves was 0.38 m.

In each greenhouse, to obtain a direct comparison between thesix treatments, the randomly selected crop row was sprayed usingthe same collectors at the same locations, but each technique

with a different mineral chelate (Chelal; BMS Micro-Nutrients NV,Belgium) (Table 1). The crop and the collectors were allowed todry completely between two successive sprayings. In both crops,three artificial collectors were placed on the crop canopy, and twoinside the canopy, as illustrated in Fig. 1. Schleicher & Schuell filterpapers (7.6×2.6 cm2, type 751; Filter Service NV, Eupen, Belgium),attached to the leaves with paper clips, were used as collectors.Using the growers’ normal practice, both crops were sprayed fromone side only.

Five non-consecutive plants were selected in both crops, so 50collector samples with deposits of the six mineral chelates wereanalysed to provide 300 deposition measurements. The depositsmeasured on the crop contours indicated the spray distribution,whereas crop penetration was evaluated by the deposits measuredon the inner collectors.

2.3 Spray deposit measurementsThe mineral chelates, used as tracers (Table 1), perform similarlyto pesticides under the same conditions. Using a different chelate,iron (Fe), cobalt (Co), copper (Cu), manganese (Mn), molybdenum(Mo) and zinc (Zn) (BMS Micro-Nutrients NV, Bornem, Belgium),allowed spray deposits from each treatment to be quantified onthe same samples. The concentration of each chelate solution wasabout 100 mg L−1. This methodology had been used by Nuyttenset al.22 to evaluate the influence of different spray boom settingson the spray deposition in tomato and pepper crops grown ingreenhouses, and Cross et al.51 – 53 used mineral chelates as atracer to evaluate the effect of spray liquid flowrate, spray qualityand air volumetric rate on the spray deposits and losses froman axial-fan orchard sprayer in different-sized apple trees. Thesemineral chelates are used as horticultural leaf fertilisers, and hencetheir use in normal concentrations does not damage the crop.Inductively coupled plasma (ICP) analysis (VISTA-PRO; Varian, PaloAlto, CA) was used to determine metal concentrations on the filterpaper collectors after extraction with 0.16 M nitric acid (HNO3)(66 + %, p.a.; Acros Organics, Geel, Belgium). Earlier experimentsindicated that there was no interference between the mineralsCo, Cu, Mn and Zn with the ICP analysis. The detection limits innitric acid for Co, Cu, Mn and Zn were very low (5, 3, 10 and 10ppb respectively).54 Furthermore, mineral chelates are stable, anda high recovery can be achieved for each of them.55

Based on the concentration measurements of the actual chelatesolution in the tank, the calculation of the real application rate(Table 1) and the analysis of the blank samples (i.e. collectorsnot exposed to any chelate solution), the concentrations ofthe minerals measured on each collector were normalised to aconcentration of 100 mg L−1 in the tank and an application rate of1000 L ha−1.

2.4 Statistical analysisThe normalised concentrations on each collector were firstexpressed as relative values (%) compared with the maximalfeasible deposition, assuming a perfectly uniform distribution ofthe spray liquid on the contours of the crop canopy, as described inFig. 1. These relative values were transformed by an arcsin squareroot transformation before statistical analysis. Factorial analysis ofvariance (ANOVA) was used to study the effect of the sprayingtechnique (TECHN) and the collector position (POS). This was donefor the deposits on the plant contours (sample points 1, 2 and 3) andfor the inner plant deposits (sample points 4 and 5) separately. Asthe interaction term TECHN×POS was never significant (P > 0.05),

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Figure 1. Positions of the filter papers within the crop canopy and settings of the spray equipment for the strawberry (A) and tomato (B) crop.


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Acd ab abc d bcd a

Ba c b

Figure 2. Relative deposition (%) on the contours of strawberries, depending on nozzle type (A) and position collector (B). 100% represents the maximalfeasible deposition, assuming a perfectly uniform distribution of the spray liquid on the contours of the crop canopy. Box plots labelled with all differentletters (from a to d) are significantly different; those having a label in common are not (Tukey multiple comparison, P < 0.05). Box plots presentnon-outlier range, 25–75% range, outliers, mean ( ) and median ( – ).

the analysis was reduced to a main-effects ANOVA. Significantdifferences were assessed by Tukey’s post hoc test. A P-value of<0.05 was considered to be statistically significant. All analysiswas done in Statistica 8.0 (Statsoft Inc., Tulsa, OK).

3 RESULTS AND DISCUSSION3.1 Influence of the sample pointsFigures 2, 3, 4 and 5 present the measured deposits in strawberriesand tomatoes as relative values (%), where 100% representsthe maximal feasible deposition, assuming a perfectly uniformdistribution of the spray liquid on the contours of the crop canopy.For each spray technique (A) and sample point (B), the deposits onthe plant contours and at the inner plant canopy are presented.The experiments showed a substantial influence of the samplingpoint on deposition. For almost each crop-specific canopy zone,deposition was significantly different depending on the positionof the sample. Only sample points 2 and 3 on the contours ofthe tomato crop showed no significant difference in deposition(Fig. 4B). The variation in positioning of both the sample points(depth in canopy) and the collectors (orientation with respectto spray cloud, shielding of leaves or stems, exposure to run-off)explains the important variability of the deposits measured at eachsample point.

3.2 Effect of the spraying systemThe type of spray system clearly influenced deposition. Onstrawberry, the spray gun (nozzle type D 1.5) resulted in adeposition rate on the crop contours of only 20.5%, while thevertical boom gave higher deposits for all nozzle types tested,varying from 26.5 to 63.1% (Fig. 2A). Sample points 2 and 3 on theside of the canopy were more exposed to the spray cloud, yielding,on average, higher deposits (Fig. 2B). The deposit on the top ofthe canopy, where sample point 1 was situated, was only 4.5% forthe spray gun, whereas the mean deposition for the treatmentswith the spray boom amounted to 13.1%. When using the spraygun, the deposits measured on the collectors positioned inside thecrop canopy (sample points 4 and 5) were significantly lower thanthose measured for the treatment performed with vertical spraybooms equipped with Lechler ID 12002 nozzles (Fig. 3A). This canbe explained by the fact that the smaller spray droplets producedby the spray gun at 1000 kPa lacked sufficient momentum topenetrate into the canopy. Figure 3B illustrates that less sprayliquid reached sample point 5 because of its position deeper inthe canopy.

In the tomato crop, a similar result was found: both on thecontours and at the inside of the canopy, the lowest depositionrates were measured when spraying with the air-assisted spouts.On the contours, a deposition rate of 18.0% was achieved with


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Aa a a b a a

Bb a

Figure 3. Relative deposition (%) on the inside of strawberries, depending on nozzle type (A) and position collector (B). 100% represents the maximalfeasible deposition, assuming a perfectly uniform distribution of the spray liquid on the contours of the crop canopy. Box plots labelled with differentletters are significantly different (Tukey multiple comparison, P < 0.05). Box plots present non-outlier range, 25–75% range, outliers, mean ( ) andmedian ( – ).

the reference spray equipment, whereas the spraying with thestandard vertical boom resulted in higher deposits, irrespective ofnozzle type, varying from 35.8 to 52.7% (Fig. 4A). At the inside ofthe canopy, the air-assisted spray (reference spray) only deposited1.2%, while the vertical boom spray gave significantly higherdeposits for all nozzles, varying from 6.8 to 17.0%. During the trialsit had already been observed that the spray cloud did not coverthe desired crop zone sufficiently as it was partly blown over thetop of the crop and deposited on neighbouring plant rows, on thesoil or on the greenhouse frame and cladding. The nozzle settings(height and orientation) were inappropriate to cover the collectorsplaced on sample points 3 and 5.

3.3 Effect of nozzle type, size and pressureFigures 2A and 3A (strawberries) and Figs 4A and 5A (tomatoes)show important differences for the different types of nozzle. Instrawberries, the highest deposits were on the contours of thestrawberry crop with the Lechler ID 12002 air-inclusion flat-fannozzle, the Albuz AVI-Twin 11002 twin air-inclusion flat-fan nozzleand the TeeJet XR 11003 extended-range flat-fan nozzle, all attheir recommended working pressures of 600, 600 and 250 kParespectively. Inside the crop canopy, the highest deposits weremeasured for the Lechler ID 12002 air-inclusion flat-fan nozzle.

Using air-inclusion nozzles, there is often a concern that, becauseof the larger droplets, an increased run-off and a reduction inefficacy of pesticides may occur.56,57 Other researchers have foundthat application of coarse droplets does not decrease field efficacyif the operator is given information on how to make initial nozzleselections and optimise their performance.49,58,59 Although thedroplet sizes and velocities of a pre-orifice flat-fan nozzle, theTeeJet DG 11003, were between those of an extended-range flat-fan nozzle and an air-inclusion flat-fan nozzle,40 deposits werelower in strawberries. As expected, the air-inclusion flat-fan nozzle(Lechler ID 12002) produced the coarsest droplet size spectrum[volume median diameter (VMD) = 374 µm] (Table 1) with thehighest average volumetric droplet speed (8.89 m s−1), resultingin a high momentum and capacity to penetrate the crop canopy.The lower average volumetric droplet speed (6.80 m s−1), resultingin a lower momentum, led to a poorer penetration capacity of theTeeJet DG 11003 nozzle and thus to lower deposits inside thecrop canopy. However, this does not explain the inferior depositsmeasured on the contours of the strawberry canopy for thisnozzle. Similarly, the finer spray quality (VMD = 184.0 µm) andlow one-dimensional average volumetric droplet speed (1.26 ms−1) of the Albuz AVI-Twin 11002 nozzle explain the bad croppenetration and low deposit inside the plant canopy, especially as


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Bb a a

b ab ab a b bA

Figure 4. Relative deposition (%) on the contours of tomatoes, depending on nozzle type (A) and position collector (B). 100% represents the maximalfeasible deposition, assuming a perfectly uniform distribution of the spray liquid on the contours of the crop canopy. Box plots labelled with differentletters are significantly different (Tukey multiple comparison, P < 0.05). Box plots present non-outlier range, 25–75% range, outliers, mean ( ) andmedian ( – ).

this type of nozzle projects the liquid in two separate sprays,oriented 30◦ forwards and backwards. In addition, sprayingwith an extended-range flat-fan nozzle (TeeJet XR 11002) wellabove its recommended pressure range resulted in the worstdeposition, both on the contours and the inside of the crop.This type of small-sized extended-range flat-fan nozzle at 600 kPaproduced a much lower VMD (187.0 µm) than the air-inclusionnozzle.

Similar results were found in tomatoes (Figs 4A and 5A). Onthe contours, the Albuz AVI-Twin 11002 nozzle performed best,followed by the TeeJet XR 11003 nozzle and the TeeJet DG11003 nozzle, all used within their recommended pressure range.Differences in deposition with these three nozzles were notstatistically significant, but the TeeJet XR 11003 extended-rangeflat-fan nozzle tended to give the best crop penetration. In contrastto the experiments in strawberries, the TeeJet DG 11003 pre-orificeflat-fan nozzle performed better in tomatoes, particularly for cropcontour deposition. This is probably caused by differences inspray boom set-up and crop characteristics. The deposition forthe Albuz ATR orange hollow-cone nozzle and TeeJet XR 11002extended-range flat-fan nozzle used at a high pressure decreasedrapidly going deeper into the crop. The lower VMD of 82.7 µmand 191.8 µm, respectively, caused by the high working pressure,

resulted in a lower penetration capacity and a (slightly) worsedeposition on the crop contours.

4 CONCLUSIONSRegardless of the kind of nozzle fitted on the vertical sprayboom, in general, this spray technique performed better than thereference spray equipment in strawberries as well as in tomatoes.Hence, this is a promising technique for applying plant protectionproducts in a safe and efficient way in these crops. Especially forthe reference spray equipment used in tomatoes, an appropriatesetting of the air-assisted spouts could lead to far better depositionresults.

The experiments also showed the importance of a well-considered nozzle choice when using a standard vertical sprayboom. Selection of the appropriate nozzle type significantlyaffected spray deposition and crop penetration. The highestdeposits in strawberries, both at the contours and at the inside ofthe crop canopy, were achieved using air-inclusion or extended-range flat-fan nozzles at their recommended spray pressure. Thetwin air-inclusion flat-fan nozzle gave sufficient deposits on thecontours of the strawberry crop, but showed a tendency to depositless inside the crop canopy.


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c bc b b c aA

aB

b

Figure 5. Relative deposition (%) on the inside of tomatoes, depending on nozzle type (A) and position collector (B). 100% represents the maximal feasibledeposition, assuming a perfectly uniform distribution of the spray liquid on the contours of the crop canopy. Box plots labelled with all different letters(from a to c) are significantly different; those having a label in common are not (Tukey multiple comparison, P < 0.05). Box plots present non-outlierrange, 25–75% range, outliers, mean ( ) and median ( – ).

In tomatoes, of the five nozzle types evaluated with a standardvertical spray boom, the extended-range flat-fan nozzle and thetwin air-inclusion flat-fan nozzle performed best, closely followedby the pre-orifice flat-fan nozzle. Again, all were used at a pressurewithin the recommended pressure range.

Furthermore, using the small-size extended-range flat-fannozzles at a pressure above the recommended pressure rangeresulted in lower deposits, especially inside the crop canopy.Because this is still common practice with many growers, thefindings of these trials are a very important tool to direct them toa more appropriate spraying technique.

ACKNOWLEDGEMENTSThe authors wish to acknowledge the Flemish Government fortheir financial support. They also thank the ‘Praktijkcentrum voorLand- en Tuinbouw’, the local growers and the ILVO techniciansfor supplying equipment, greenhouses and technical support.

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Documents

Effect of spray application technique on spray deposition in greenhouse strawberries and tomatoes