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Author's personal copy
Crop Protection 41 (2012) 77e87
Contents lists available at SciVerse ScienceDirect
Crop Protection
journal homepage: www.elsevier.com/locate/cropro
Spray deposition and distribution in a bay laurel crop as affected by nozzle type,
air assistance and spray direction when using vertical spray booms
Dieter Foqué a, *, Jan G. Pieters b, David Nuyttens a, *
a
b
Institute for Agricultural and Fisheries Research (ILVO), Technology and Food Science Unit, Agricultural Engineering, Burg. Van Gansberghelaan 115, bus 1, 9820 Merelbeke, Belgium
Ghent University, Department of Biosystems Engineering, Faculty of Bioscience Engineering, Coupure Links 653, 9000 Ghent, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 December 2011
Received in revised form
14 May 2012
Accepted 20 May 2012
In Flanders, greenhouse growers predominantly use handheld sprayers instead of spray boom equipment. Nevertheless, handheld sprayers have several drawbacks. Growers increasingly recognize the
advantages of spray boom equipment, which has resulted in increasing adoption of spray boom systems.
Some growers still doubt the efficacy of spray boom systems, however, while others have questions
about their use. In this study, we aimed to address both doubts and questions by optimizing a vertical
spray boom application for a bay laurel crop using air support and spray angling. Spray deposition on the
stem and the upper and lower side of the leaves was measured using mineral chelates as tracers at
twenty collector positions in the top and bottom as well as in the front, back, left and right zone of the
plant. Four plant repetitions were used for every spray event. Nine different application techniques were
tested in three repetitions in laboratory conditions using a fully automated spray system. The effect of
nozzle type, angled nozzles, air support and spraying in two passes with an opposite direction was
evaluated. The experiments showed that collector position and application technique had a significant
effect on deposition. However, angling the spray, using air support or spraying in two consecutive passes
with an opposite direction did not result in a higher deposition or penetration capacity compared with
the standard vertical spray boom. Nevertheless, some techniques might still result in a higher bioefficacy due to a more homogenous liquid distribution. The use of a vertical spray boom is a promising technique for safe and efficient application of plant protection products in a vertical crop. Nozzle
choice, spray boom setting, spray distance and the air speed of air assisted sprayers require careful
consideration, however. Of the tested techniques, the applications made with an extended range standard flat fan nozzle without air support, directed straight toward the crop and used with a fixed spray
distance of 30 cm to the stem generally produced the best spray results in the considered, conically
pruned bay laurel crop.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Spray application technique
Nozzle type
Spray angling
Spraying in 2 passes
Spray distribution
Ornamental crops
1. Introduction
In 2006, we began researching the optimization of the spray
equipment and technology used in various ornamental crops in
Flanders (Belgium) in collaboration with the Research Center for
Ornamental Plants (PCS). We first surveyed several greenhouse
growers about the spray equipment and technology they used for
their plant protection needs. That enquiry revealed that most of
them use spray guns and spray lances for crop protection and that
persistent pests and diseases are common. We also gathered
* Corresponding authors. Tel.: þ32 9 272 28 00; fax: þ32 9 272 28 01.
E-mail addresses: [email protected] (D. Foqué), david.nuyttens@
ilvo.vlaanderen.be (D. Nuyttens).
0261-2194/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cropro.2012.05.020
information on the spray parameters used by the growers. Most of
them use their equipment at high pressures (up to 50 bar) and low
travelling speeds, which results in relatively high spray volumes
(2000 l ha1 and more). These results were similar to data gathered
from surveys in 2004 (Braekman and Sonck, 2008; Goossens et al.,
2004) and 2005 (Vissers, pers. Comm.). Many growers still believe
that high spray volumes or spray pressures assure good plant
protection (Braekman and Sonck, 2008; Goossens et al., 2004).
However, both older and newer surveys (Braekman and Sonck,
2008) indicated that this approach does not give the desired
results. Furthermore, the growers’ opinion disagrees with literature. Derksen et al. (2001) reported that high-pressure sprays had
a lower penetration capacity and did not result in a better coverage
when compared to low-pressure sprays. Sánchez-Hermosilla et al.
(2003) showed that the spray deposition of a vertical boom in
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
a tomato crop after application at 750 l ha1 and a spray pressure of
15 bar was comparable to that of a spray gun application with
a spray volume of 2000 l ha1 and a spray pressure of 38 bar. van Os
et al. (2005) found that decreasing the spray pressure to 5 bar
provided adequate depositions and lead to reduced chemical losses
in a tomato crop. Prokop and Veverka (2006) proved that poor leaf
coverage can only be partly compensated by higher spray volumes.
Braekman et al. (2009, 2010) demonstrated that higher relative
deposition can be obtained with a spray boom compared to a spray
gun, regardless of the nozzle type used, and that the spray volume
can be reduced by using a spray boom instead of a spray gun or
lance. Additionally, Braekman et al. (2010) showed that using small
extended-range flat fan nozzles at a pressure above the recommended pressure range resulted in significantly lower depositions,
especially inside the canopy. Sanchez-Hermosilla et al. (2011)
concluded that spray gun applications often result in inadequate
penetration in the canopy, heavy losses to the ground due to leaf
run-off, and insufficient deposition on the underside of the leaves.
These studies all indicate that using a spray gun at a higher spray
volume and pressure does not result in improved pest control.
Nevertheless, when confronted with unresponsive or resistant
plagues and diseases, growers still tend to increase their spray
frequency, spray pressure, and spray volume. In some cases, they
also repeatedly use the same active ingredients. These practices
only increase the risk of increased resistance of pest and diseases.
Furthermore, since most plant protection products authorized for
ornamentals in Belgium prescribe the dose needed as a concentration (e.g., 50 g 100 l spray volume, (Anon., 2012a)), these high spray
volumes mean higher potential exposure risks for the applicator
and the environment (Bjugstad and Torgrimsen, 1996; Hughes
et al., 2006; Machera et al., 2009; Vidal et al., 2002).
In addition to the exposure risks and higher pressures and
application rates used, spray gun techniques are also known to
result in less uniform spray results and higher labor costs when
compared to spray boom equipment (Braekman et al., 2009, 2010;
González et al., 2009; Knewitz et al., 2003; Langenakens et al.,
2002; Molto et al., 2000; Nuyttens et al., 2004, 2009b; SánchezHermosilla et al., 2003, 2011; Subramanian et al., 2005; Vidal
et al., 2002). Growers are increasingly recognizing the advantages
of spray boom systems and many are switching to spray boom
systems (Braekman and Sonck, 2008; Goossens et al., 2004). Many
growers have questions about spray boom systems, e.g. which
application technique to use, the maintenance of the selected
equipment and optimal settings for it, choosing the right nozzle
type for their crop, etc. Still others doubt the efficacy of spray boom
systems. Many growers also believe that spray boom systems are
expensive, fear that they would be difficult to use in narrow
passageways between plant rows, and doubt that they would be
applicable given the diversity in plants and production systems
found within the same company.
To address some of these questions, several spray boom prototypes have been built and assessed in field (Braekman et al., 2009)
and laboratory trials (Foqué et al., 2012). Additionally, the deposition of spray liquids using spray boom techniques was optimized
for 2 important ornamental crops grown in Flanders: ivy (Hedera
sp.) and bay laurel (Laurus nobilis). These tests were carried out
under laboratory conditions in ILVO’s Spray Tech Lab (Anon.,
2012b). For ivy (Foqué and Nuyttens, 2011a, 2011b; Foqué et al.,
submitted for publication), a horizontal spray boom was used. For
bay laurel, a vertical spray boom system was used (Foqué et al., in
press; Nuyttens et al., 2009a).
For the bay laurel crop, the first tests revealed an optimal spray
volume of 4900 l ha1 ground surface corresponding with
1470 l ha1 crop surface (Foqué et al., in press; Nuyttens et al.,
2009a). The extended range flat fan (XR 110 03), the Venturi flat
fan (ID 120 02) and the hollow cone nozzle type (TXB 80 02), led to
the highest depositions in a conically pruned bay laurel pot plant
crop (Foqué et al., in press; Nuyttens et al., 2009a). The plants used
for these trials were 1.00e1.20 m high and had a maximum base
diameter of 0.50 m. Despite a relatively high application rate,
particularly when compared to those used spraying arable crops
(25e200 l ha1)(Butler Ellis and Scotford, 2003), fruits
(50e500 l ha1) (Cross et al., 2001a), field-grown vegetables
(150e400 l ha1) (Jensen and Nielsen, 2008; Piché et al., 2000), or
ornamental liners (187e374 l ha1) (Zhu et al., 2011), this would
already mean a significant reduction of the pesticides applied
compared to the rates now used by bay laurel growers using their
standard technique (spray gun application, up to 7000 l ha1)
(Foqué et al., in press; Nuyttens et al., 2009a). Many studies
describe that angling the nozzles is an efficient, easily adjustable,
and inexpensive way to improve the deposition or penetration in
the canopy of the crop (Combellack and Richardson, 1985; Derksen
et al., 2007b, 2010; Dorr, 1990; Foqué and Nuyttens, 2011a, 2011b;
Göhlich and Jegatheeswaran, 1976; Jensen and Spliid, 2005; Jensen,
2007, 2012; Lee et al., 2000; Richardson, 1987; Sayinci and
Bastaban, 2011; Tunstall et al., 1965). Air support (Derksen et al.,
2001; Foqué and Nuyttens, 2011a; Foqué et al., submitted for
publication; Gan-Mor et al., 1996; Lee et al., 2000; Ozkan et al.,
2006; Panneton et al., 2005; Panneton and Piché, 2005; Turner
and Matthews, 2001; Val et al., 1996; van de Zande et al., 2002;
Vandermersch et al., 2001) or a combination of both air support and
an angled spray (Foqué and Nuyttens, 2011a; Foqué et al.,
submitted for publication; Panneton et al., 2000; Scudeler and
Raetano, 2006; Womac et al., 1992) also shows promising results.
Treating the crop from 2 directions has been suggested to overcome
lower deposition on the back side of the plants (Derksen et al.,
2007a, 2008).
We therefore studied the effect of nozzle type, angled nozzles,
air support and spraying in 2 passes with an opposite direction for
vertical spray boom applications. The results were then compared
to the standard spray boom application using the optimal settings
for a bay laurel crop as suggested by our first set of experiments in
bay laurel (Foqué et al., in press; Nuyttens et al., 2009a).
2. Materials and methods
2.1. Spray application techniques
A self-propelled aluminum spray unit described by Foqué and
Nuyttens (2010, 2011b) was equipped with 2 vertical spray
booms and 2 sleeve-like air support systems, mimicking the Hardi
Twin air support system (Foqué and Nuyttens, 2011a; Nuyttens
et al., 2007a) (Fig. 1). Nine spray application techniques were
tested to evaluate the effect of nozzle spray direction (standard (0 ),
forward (30 ) or backward (30 ) relative to the movement of the
spray boom), spraying with or without air support or using 2
successive sprays in an opposite direction (Table 1). Based on Foqué
et al., in press, 3 nozzle types were tested, i.e. the extended range
flat fan TeeJet XR 110 03 nozzle, the hollow cone TXB 80 02 nozzle
and the Venturi flat fan ID 120 02 nozzle. Volume median diameters (VMD) of these nozzle-pressure combinations were determined without air assistance, at 0.50 m distance from the nozzle
using a PDPA laser-based measuring setup (Nuyttens et al., 2007a,
2009c). The application technique with the standard 0 spray
direction without air support and use of the extended range flat fan
nozzles (XR 0 NA) is defined here as the standard technique. Based
on the results of previous experiments with a horizontal spray
boom system (Foqué and Nuyttens, 2011a; Foqué et al., submitted
for publication; Panneton et al., 2000; Panneton and Piché, 2005),
the air support was set to 30 m s1 at the air outlet. The nozzle
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
Fig. 1. Automated tunnel sprayer equipped with 2 horizontal spray booms and 2 sleeve-like air support systems:
vertical spray boom,
aluminum frame of the setup.
spacing and boom settings were derived from previous tests (Fig. 2)
and applications were made with the suggested application rate by
Foqué et al., in press of 1470 l ha1 crop surface. Unlike in the
preceding trial (Nuyttens et al., 2009a; Foqué et al., in press) and
based on earlier findings (Braekman et al., 2009, 2010; Foqué and
Nuyttens, 2011a, 2011b; Nuyttens et al., 2004), a fixed spraying
distance of about 30 cm to the outermost leaves of the canopy was
maintained instead of 30 cm to the main stem of the bay laurel crop
(Foqué et al., in press). Because of the resulting bigger distance
between rows (about 1.10 m instead of 0.60 m in Foqué et al., in
press)) the application rate of 1470 l ha1 crop surface corresponds with 2600 l ha1 of ground surface. This application rate is
still quite high, but already closer to the minimum application rate
that is often suggested by manufacturers to treat ornamental crops
in greenhouse conditions (1000 l ha1).
Each spray application was repeated 3 times except for the application with a forward spray angle, made in 2 successive sprays (XR 30
NA (2)), because one repetition was made at a wrong spray pressure.
2.2. Experimental setup
The experimental setup was very similar to the setup described
in and Foqué et al., (in press). Nine conically pruned bay laurel pot
plants (L. nobilis, 1.00e1.20 m high and maximum 0.50 m base
diameter, approximately eight years old) were placed in a single
79
rails of the automated spray track,
sleeve-like air assistance,
row. Four of them were equipped with deposition collectors
(Fig. 2). The inter-plant distance (stemestem) was 55 cm.
2.3. Spray deposition measurements
To evaluate spray deposition and penetration in the canopy, 9
mineral chelate tracers (B, Ca, Co, Cu, Fe, Mg, Mn, Mo and Zn) and
filter paper collectors (FPCs, Schleicher & Schuell, 5.6 cm 2.5 cm,
2589 D, Filter Service NV, Eupen, Belgium) were used. These
chelates, all commercially available as horticultural leaf fertilizers
(ChelalÒ; BMS Micro-Nutrients NV, Belgium), were mixed with tap
water to result in a tank mix of about 1.0 g L1. Except for B, Ca and
Mg, our research group had successfully used these mineral chelate
tracers in previous experiments (Braekman et al., 2009, 2010;
Foqué and Nuyttens, 2011a, 2011b; Foqué et al., in press, 2012,
submitted for publication; Langenakens et al., 2002; Nuyttens et al.,
2004, 2009a, 2009b). Furthermore, the reliability of the tracer
method has been confirmed (Cayley et al., 1987; Cross et al., 2001a,
2001b, 2003; De Moor et al., 2002; Garcia-Ramos et al., 2009; Gil
et al., 2007; Murray et al., 2000).
The FPCs were placed on 20 positions in each of the 4 collector
plants (Fig. 2). These were: the stem (S), the leaves’ upper side (L
up) and the leaves’ underside (L un) in 2 crop zones (zone I (Z1) and
zone II (Z2)). Because of the small size of the leaves and to prevent
contamination caused by run-off, smaller sized FPCs were used for
Table 1
Overview of the spray application techniques and spray parameters considered.
No. of
repetitions
Technique
3
3
3
3
3
3
3
3
2
IDa 0 A
ID 0 NA
TXBb 0 A
XRc 0 A
XR 0 NA
XR 30 A
XR 30 NA
XR 30 NA
XR 30 NA (2)
a
Direction of
the spray ( )d
VMD (mm)e
0
0
0
0
0
30
30
30
30
e
311.6 23.1
168.3 1.6
e
179.9 6.5
e
e
e
e
Air
support
Spray
pressure
(bar)
Speed
(km h1)
Nominal flow
rate (L min1)
Application rate (l ha1 ground surface)
Yes
No
Yes
Yes
No
Yes
No
No
No
6.9
6.9
7.0
3.1
3.1
3.1
3.1
3.1
3.1
2.47
2.55
2.52
2.36
2.45
2.37
2.40
2.39
4.88
1.22
1.22
1.20
1.18
1.18
1.18
1.18
1.18
1.18
2664
2614
2510
2629
2640
2655
2644
2637
2571
Totalf
34
58
134
89
31
51
34
45
106
Z1g
Z2h
1598
1568
1506
1578
1584
1593
1586
1582
1543
1066
1045
1004
1052
1056
1062
1058
1055
1028
ID 120 02: Venturi flat fan nozzle, Lechler GmbH, Metzingen, Germany.
TXB 80 02: hollow cone nozzle, TeeJet Technologies, Wheaton, U.S.
c
XR 110 03: extended range flat fan nozzle, TeeJet Technologies, Wheaton, U.S.
d
Direction of the spray relative to the movement of the spray boom: a forward (30 ), backward (30 ) or a spray aimed directly towards the crop (0 ) was used.
e
Volume median diameter below which smaller droplets constitute 50% of the total volume. Three replica measurements were made for each nozzle type (mean SD). All
measurements were made without air assistance.
f
The spray volume is presented as the mean application rate overall sprays (mean SD).
g
6 out of 10 nozzles aimed to crop zone 1 (Fig. 2).
h
4 out of 10 nozzles aimed to crop zone 2 (Fig. 2).
b
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
Fig. 2. Experimental setup and the different collector positions.
the underside collector positions (3.8 cm 2.5 cm). In Z1, leaf
collectors were placed in the front (F), back (B), left (L) and right (R),
relative to the spray boom movement; in Z2, leaf collectors were
only located on the front and back sides of the collector plants
(Fig. 2). In addition to the 4 plant repetitions, 3 spray repetitions per
application technique were performed (Table 1). For each set of 9
spray applications, a new set of FPCs and a different mineral chelate
tracer per application technique was used.
After each spray event, the exact tank concentration was
determined by taking 4 tank samples (200 ml per collector) and the
FPCs were allowed to dry completely before making a new application. After 9 spray applications, the FPCs were gathered and
analyzed by inductively coupled plasma analysis (ICP analysis,
VISTA-PRO, Varian, Palo Alto, CA, USA). The amount of tracer liquid
deposited onto each collector (l ha1) was calculated. This calculation accounted for the actual concentration in the tank, the
application rate, the size of the collector, the quantity of 0.16 M
nitric acid (66þ%, pro analysis, Acros Organics, Geel, Belgium) used
for extraction, and the results of the analysis of the blanks.
2.4. Statistical analysis
In this experiment, 2160 deposition measurements were made
(20 collector positions 4 collector plants 9 tracers 3
repetitions). The deposition results were also expressed as relative
deposition values (%), as done in previous experiments (Braekman
et al., 2010; Foqué et al., submitted for publication, in press, 2012;
Nuyttens et al., 2009a). Although the differences in actual application rates are rather small (Table 1), this allowed for a more direct
comparison between techniques.
The datasets was examined for normality using ShapiroeWilk’s
normality test but didn’t prove to have a normal distribution and
(W ¼ 0.76, p < 0.001) and showed a distinct right skewness. To
examine whether parametric statistical tests could be used for
further analysis, the relative deposition dataset was transformed
using a natural (base e) logarithm and base square root and
assessed for normality as described above. To allow logarithmic
transformation, the absolute depositions equal to zero were
replaced by a deposition of 1.38 l ha1, which corresponds to the
detection limit of the ICP-analysis (0.01 103 g L1). The square
root transformed relative datasets (W ¼ 0.96, p < 0.001) showed
the most promising ShapiroeWilk’s test results. A factorial ANOVA
was used to examine the effect of the application technique and the
collector position. The interaction term technique collector
position was significant (F(171, 1816) ¼ 1.61, p < 0.001) and resulted in
62 homogenous groups shown by the post hoc test (Duncan).
Because of the impracticality of discussing all of these significant
differences in one paper, the deposits made to the same collector
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
position are compared to the standard XR 0 NA application technique defined as a vertical spray boom system, equipped with XR
110 03 nozzles without air support and with a standard 0 spray
direction (nozzles aimed directly towards the crop). This technique
also showed good results in previous tests (Foqué et al., in press;
Nuyttens et al., 2009a). Significant differences are indicated by * in
Figs. 6e8.
Additionally, all spray application techniques with a 30 forward
spray direction were compared to the XR 30 NA spraying technique. This allowed an assessment of the individual effect air
support (XR 30 A) or 2 subsequent sprays with an opposite
direction (XR 30 NA (2)) for the same nozzle type (XR) and spray
direction (30 ). Significant differences are indicated by > in
Figs. 6e8.
Furthermore, the deposition results of the same application
technique at different collector positions in the same plant zone
were compared. Four plant zones were defined, i.e. upper side of
the leaves in ZI, upper side of the leaves in ZII, lower side of the
leaves in ZI and upper side of the leaves in ZII. Significantly different
depositions are given a different letter label in Figs. 6e8.
To evaluate the individual effect of nozzle type with and without
air support, an additional analysis was made that only used the
spray boom configurations with a standard 0 spray direction
(Table 1). Doing so, the interaction term technique collector
position was no longer significant and a main effect ANOVA could
be used. Both technique (F(4, 1053) ¼ 11.82, p ¼ 0.001) and collector
position (F(19, 1053) ¼ 39.37, p < 0.001) showed a significant impact
on deposition. The differences between the collector positions were
assumed to be the same for all techniques, therefore only the
differences between techniques are discussed in this paper (Fig. 5).
Again, a Duncan post hoc test was used to investigate the differences between techniques.
Because a different spray distance to the crop was used in the
first series of experiments (Nuyttens et al., 2009a; Foqué et al., in
press), these experiments allowed an evaluation of the effect of
spray boom distance to the crop for the XR 0 NA and the ID 0 NA
technique as these techniques were included in both series of
experiments. In contrast to the above, the square root transformed
absolute dataset could be used for further parametric statistics. The
transformed dataset showed a distribution close to Gaussian
(W ¼ 0.96, p < 0.001). Again, a factorial ANOVA was used to
examine the effect of the application technique and the collector
position. The interaction term technique collector position was
again significant (F(171, 1816) ¼ 2.06, p < 0.001) and the post hoc test
81
(Duncan) revealed 22 homogenous groups. Only the differences in
depositions at the same collector position are discussed (Fig. 9).
As both transformed datasets did not show a perfect normal
distribution, the residuals of the statistical models were examined
as well. Given that the residual values were all normally distributed
(Fig. 3), the model had a high explanatory value.
All statistical analysis were performed with Statistica 9.1 (Statsoft Inc., Tulsa, OK, USA). A p-value less than 0.05 was considered
statistically significant.
3. Results and discussion
3.1. Influence of collector position
The factorial ANOVA analysis showed that collector position had
a significant effect. The differences between all 20 collector positions are shown in Fig. 4. This graph gives a good idea about the
average depositions on the different collectors and the relations
between them.
In general, a significantly higher deposition was found on
collectors on the front side of the plant compared with corresponding collectors on the back side of the plant (e.g. Z1 L B b vs. Z1
L F b). Since the interaction term (technique collector position)
was significant as well, these significant differences between the
back side and the front side were not necessarily observed with all
application techniques. In Figs. 6e8 it is shown that for some
techniques, the difference between front and back is no longer
significant although the same trend was followed in most cases.
Other techniques, however, resulted in a more homogeneous
deposition on the 4 comparable collector positions as discussed
below.
The relative depositions in Z2, however, were generally lower
than those in Z1, even though the results are expressed relative to
the spray volume used (Figs 4, 6e8). This was a direct consequence
of the lower spray volume applied to this zone due to a smaller
number of nozzles used in the upper canopy (Table 1, Fig. 2) based
on previous experiments (Nuyttens et al., 2009a; Foqué et al., in
press).
3.2. Influence of spray application technique
When all spray application techniques were assessed in 1
dataset, a significant interaction between technique and collector
position was found. This indicates that the relationship between
Fig. 3. Residuals of the statistical models used. (A) The residual values of the ANOVA used to compare the different techniques used in present study. (B) The residual values of the
ANOVA used to compare the depositions made by the XR 0 NA and ID 0 NA technique techniques included in both trials.
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
Fig. 4. The effect of collector position as shown by the factorial ANOVA, based on the
square transformed, relative deposition dataset. Collector positions that significantly
differ in deposition have a different letter label.
the different collector positions was no longer the same for all
techniques considered. The effect of application technique is discussed in more detail.
3.2.1. Standard application technique
Except for the optimized spray boom settings (Nuyttens et al.,
2009a; Foqué et al., in press), the extended range flat fan nozzle
type without air support, pointed directly toward the crop (XR
0 NA) was very little different from the vertical spray boom
technique generally used in practice. This technique was thus
defined as the standard technique in this paper. None of the tested
techniques resulted in significantly higher depositions (Figs. 6e8).
Consequently, it can be accepted that this application method
produced the most optimal spray deposits in this bay laurel crop
considered.
The standard XR 0 NA technique, however, did show some
significant differences in deposition between the collector positions attached to the upper side of leaves in Z1 (Fig. 6A). Highest
deposits were found in the front, followed by the right, the left and
the back of Z1. The difference between front and back is caused by
the direction of movement of the spray and the resulting shading
effect of the crop (Derksen et al., 2007a, 2008). At the stem
collectors in Z1 (Fig. 8A), deposition on the left side of the stem was
significantly higher than on the right side, although a similar
deposition is expected. This could indicate that the depositions on
the stem in Z1 were secondary deposits caused by run-off. The less
equal liquid distribution on the stem and the upper side of the
leaves could result in a lower bio-efficacy when compared to
techniques with a more uniform spray deposition (Barber et al.,
2003; Gan-Mor et al., 1996; Nuyttens et al., 2004). Nevertheless,
growers do not consider the deposition on the upper side of the
leaves to be problematic (Foqué and Nuyttens, 2010, 2011b). In Z2,
the deposits for the standard technique showed no significant
differences between the collectors on the underside of leaves
(Fig. 7A and B) or the ones attached to the stem collector (Fig. 8B).
3.2.2. Combined effect of nozzle type and air support for the
standard 0 spray direction
To assess the combined effect of nozzle type and air support,
relative deposition values of the techniques with a standard spray
direction (0 ) were evaluated separately (Fig. 5) and compared with
the standard XR 0 NA technique. Overall, the highest relative
deposition was found for this standard technique. Using the same
standard flat fan nozzle type with air support (XR 0 A) resulted in
lower deposition values. On the other hand, the use of air support
did result in significantly higher mean relative depositions for the
Venturi flat fan nozzle type when comparing the ID 0 A configuration with the ID 0 NA configuration. The opposite effect of air
support was thus found depending on the droplet size characteristics. Together with the ID 0 NA application, the fine droplet size
hollow cone application with air support (TXB 0 A) produced the
significantly lowest mean depositions in the laurel crop.
These results indicate that the use of air support in this horizontal crop only had a positive effect for coarse droplet sprays and
no effect or even a negative effect for finer droplet sprays. This
outcome is in contrast with previous horizontal spray boom
experiments (Foqué and Nuyttens, 2011a; Foqué et al., submitted
for publication) which demonstrated a strongly positive effect of
air support in combination with the fine-to-medium extended
range flat fan nozzle and a more limited positive effect in combination with a coarse droplet spray.
The Venturi flat fan nozzle (ID 0 NA) resulted in a significantly
lower total deposition than the extended range flat fan nozzle (XR
0 NA) (Fig. 5), although no significant differences were found for
most of the individual collector positions. Only on the upwardlyoriented leaf collector positioned on the front side of the plants
in Z1, the Venturi flat fan nozzles without air support (ID 0 NA)
gave significantly lower deposits compared with the reference
technique (Fig. 6A). Moreover, the ID 0 NA technique never
resulted in significant differences between the different orientations of collectors of the same type, which was not the case for the
reference techniques. Because of the more uniform spray distribution, represented by the low C.V. value in Fig. 5, caused by the
higher penetration capacity of the coarse droplet spray (Braekman
et al., 2010; Foqué and Nuyttens, 2011b), the ID 0 NA technique
could still result in a better efficacy (Barber et al., 2003; Gan-Mor
et al., 1996; Nuyttens et al., 2004). Again, this shows the importance of selecting the right nozzle type most fitted to a specific
application.
When the Venturi flat fan nozzle was combined with air support
(ID 0 A), a higher deposition was measured on the upper side of
leaves in the front of plant zone Z1, compared with the left and the
back side of this zone (Fig. 6A). No other significant differences
were found in the different plant zones (Figs. 6e8) indicating
a relative uniform canopy spray distribution. The ID 0 A technique,
Fig. 5. The means (mean SE) and coefficients of variation (C.V.) of the relative
depositions of 3 nozzle types (ID: Venturi flat fan ID 120 02; TXB: hollow cone TXB 80
02 and XR: extended range flat fan TeeJet XR 110 03) used with a normal 0 orientation
of the spray, with (A) or without (NA) air support. Bars with a different label are
significantly different.
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
83
a horizontal boom application (Foqué and Nuyttens, 2011a; Foqué
et al., submitted for publication; Panneton and Piché, 2005;
Womac et al., 1992), no resistance is given to the spray past the
canopy, increasing the risk of blowing the spray beyond the foliage
of a single crop row. With a horizontal boom, fine to medium sprays
will still result in secondary deposits due to the turbulence that
occurs when the air flow hits the soil. For a vertical approach, the
air support should be set in a way that the wind speed is high
enough to overcome the resistance of the foliage but does not blow
the spray past the canopy. When the crop is treated from 2 sides at
the same time, the colliding nebulas will probably further improve
the deposition in the crop. Therefore, in addition to the boom
settings and nozzle type (Braekman et al., 2010), the right amount
of air should be used. Based on these experiments, other than
a higher homogeneity for the XR 0 A configuration and a significantly higher deposition of the ID 0 A technique when compared
to the ID 0 NA application, the use of air support in a vertical crop
does not seem to compensate for the high cost of this technique, as
higher deposits can be achieved without air support (XR 0 NA).
The TXB 0 A application, together with the ID 0 NA technique,
resulted in the lowest overall mean relative depositions and the
highest C.V. values in the bay laurel crop (Fig. 5). Compared with
the standard technique, a significantly lower deposition was found
in the dense (LAI ¼ 0.89 0.13) (Nuyttens et al., 2009a; Foqué et al.,
in press) crop zone (Z1) on the upper side of the leaves in the front
side of the plants (Fig. 6A) and on the stem collectors at the left and
back of the plants (Fig. 8A). In Z2 (LAI ¼ 0.09 0.22) (Nuyttens et al.,
2009a; Foqué et al., in press) on the underside of the leaves
(Fig. 7B), this technique also led to significantly lower deposits on
Fig. 6. Relative deposition (mean SE) on the upper side of the leaves of the bay laurel
crop in Z1 (A) and Z2 (B), respectively. * ¼ depositions which are significantly different
from the XR 0 NA technique at the same collector position. > ¼ depositions which are
significantly different from the XR 30 NA technique at the same collector position. a,
b ¼ depositions with a different letter label are statistically different for the same
technique.
however, never resulted in significantly higher spray deposits than
the XR 0 NA technique (Figs. 5e8).
The air assisted equivalent of the reference technique (XR 0 A)
gave no significant differences between collectors in the same zone
(Figs. 6e8) except for on the upper side of the leaves in zone I
(Fig. 6A). In this zone and in agreement with the reference technique, a lower deposition was found at the back of the plant. On the
stem collectors in Z1 (Fig. 8A), the use of air support resulted in
a more uniform distribution than the reference technique although
none of the different collector positions showed a significantly
higher deposition than for the reference technique. This technique
seems to cope with the run-off problem hypothesized for the XR
0 NA technique. On the one hand, this could be explained by
a more uniform spray distribution in the crop as suggested by the
deposition on the stem in Z1 and the low C.V. value in Fig. 5. On the
other hand, the absence of run-off could also be ascribed to a bigger
portion of the spray volume that is lost due to the use of air support.
This last explanation is more likely since the overall mean deposition of the XR 0 A application was found to be lower than the one
of the XR 0 NA technique (Fig. 5).
Differences in the effect of air support depending on the nozzle
type and the corresponding droplet size spectrum (Fig. 5) reinforces the assumption that the air speed (30 m s1 at the outlet)
was too high for applications with a vertical boom in this bay laurel
crop. Drift experiments (Nuyttens et al., 2007a, 2010) demonstrated
that ID nozzle applications (coarse droplets) are less affected by the
use of air support than those made with the XR nozzle type (fine to
medium droplets) because of their bigger droplet size (Braekman
et al., 2010; Foqué and Nuyttens, 2011a, 2011b). In contrast to
Fig. 7. Relative deposition (mean SE) on the underside of the leaves of the bay laurel
crop in Z1 (A) and Z2 (B), respectively. * ¼ depositions which are significantly different
from the XR 0 NA technique at the same collector position. > ¼ depositions which are
significantly different from the XR 30 NA technique at the same collector position. a,
b ¼ depositions with a different letter label are statistically different for the same
technique.
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84
D. Foqué et al. / Crop Protection 41 (2012) 77e87
the back side compared to the front side of the plants. Because of
the lower depositions on the stem, the underside of the leaves and
the back of the plants, using a hollow cone nozzles in combination
with air assistance is less suitable for applications in a bay laurel
crop, as these difficult to reach locations in the plant are of special
importance to the growers (Foqué and Nuyttens, 2011a, 2011b).
Probably this is an effect of the air speed (30 m s1 at the outlet)
being too high as well as, in the first set of trials (Nuyttens et al.,
2009a; Foqué et al., in press), the non-air supported TXB did
result in depositions comparable to those of the XR and ID nozzle
type. This statement is supported by the conclusion of Nuyttens
et al. (2007b) that air support has the highest impact on finer
sprays.
3.2.3. Combined effect of spray direction and air support
The effect of spray direction (30 , 0 and 30 ) was evaluated
comparing the results of the XR 30 NA, the XR 0 NA and the XR
30 NA application and the XR 0 A and XR 30 A application.
No significant differences were found between the XR 30 NA
and the XR 0 NA reference technique (Figs. 6e8). However, similar
to the standard technique, the XR 30 NA application resulted in the
same significant differences between collector positions on the
upper sides of the leaves in Z1 (Fig. 6A). Also on the stem in Z1
(Fig. 8A) a higher deposition on the left side was found compared
with the back and right sides, probably due to run-off. Additionally,
the stem deposition in Z1 was significantly higher in the front
compared with the back because of the shading effect. When
a forward spray angle was used without air support, this configuration seemed to intensify the shading effect created by the canopy,
creating differences between the front and the back of the plants.
Additionally, significant differences in upper side leaf deposition
between the front and back in Z2 were observed for the XR 30 NA
as well as for the XR 30 A technique (Fig. 6B). Moreover, in Z2 at
the underside of the leaves (Fig. 7B), higher depositions were found
in the front compared to the back of the plants for the XR 30 A
technique. This confirms that a 30 spray direction increased the
shading effect and the difference in deposition between front and
back.
These findings are in agreement with Nuyttens et al. (2009a)
and Foqué et al., in press) who found that the difference between
the deposition on the front side and the back side of the plant was
most pronounced for the deflector flat fan nozzle because of its
forward spray direction. The use of air support only seems to
intensify these differences.
Compared to the reference technique, the use of a backward
spray direction (XR 30 NA) resulted in significantly lower
depositions on the upper side of the leaves in Z1 (Fig. 6A) and on
some stem collectors in Z1 and Z2 (Fig. 8). In particular, the lower
deposition values at the front of the plants were characteristic for
a 30 spray direction. In contrast to the reference technique, no
significant differences were found between alike collector positions
in the different plant zones (Figs. 6e8). Therefore, use of a backward spray direction did not result in a higher total spray deposition compared with the reference technique but it did result in
a more uniform spray distribution, which is also an important
factor with regard to a good biological efficacy (Barber et al., 2003;
Gan-Mor et al., 1996; Nuyttens et al., 2004). Womac et al. (1992)
found that orienting the air stream of an air assisted sprayer 30
backwards increased deposits on the underside of leaves. In
Braekman et al. (2010), however, an air-assisted spout fitted with an
ISO 80015 flat fan nozzle type oriented 45 upwards and 30
backwards resulted in the lowest deposits. Because the other boom
setting did result in better depositions, the authors concluded that
the air-assisted spouts could lead to even better deposition results
when appropriate setting is used. This suggests that using a backward spray angle in combination with air support could result in
further improvements.
3.2.4. Effect of the number of passes with a 30 spray direction
The effect of an application in 2 runs with an opposing direction
was evaluated for the spray boom setup with extended range flat
fan nozzles and a 30 spray direction by comparing the XR 30 NA
(2) and the XR 30 NA techniques.
The 2-run application (XR 30 NA (2)) never showed significantly different depositions for collectors attached in the same
plant zone (Figs. 5e7). This result agrees with Derksen et al. (2007a,
2008), who concluded that treating the crop in 2 directions is
a good way to overcome a lower deposition on the back side of the
plants. However, on Z1 S L (Fig. 8A) and Z1 L F up (Fig. 6A), this
technique booked significantly lower deposits than the standard
technique. As the XR 30 NA (2) application never resulted in
significantly higher depositions than the standard technique, no
statistical evidence was found for a better performance of spraying
in 2 runs with an opposite direction. However, the more uniform
spray distribution could result in an improvement (Barber et al.,
2003; Gan-Mor et al., 1996; Nuyttens et al., 2004).
Fig. 8. Relative deposition (mean SE) made to the stem in the lower (A) and upper
region (B) of the bay laurel crop. * ¼ depositions which are significantly different from
the XR 0 NA technique at the same collector position. > ¼ depositions which are
significantly different from the XR 30 NA technique at the same collector position. a,
b ¼ depositions with a different letter label are statistically different for the same
technique.
3.2.5. Effect of air support with a 30 spray direction
The effect of air support for a 30 spray direction was evaluated
by comparing the XR 30 A technique with the reference technique
and the XR 30 NA technique.
In general, the XR 30 A technique led to deposits comparable to
the ones of the XR 30 NA and XR 0 NA applications (Figs. 6e8)
except at the collector positions Z1 L B up and Z2 L B up (Fig. 6) and
Z1 L F un (Fig. 7A) where lower depositions were found compared
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
with the reference technique. Again, this might indicate the effect
of spray loss because of the use of air support. Moreover, in contrast
with the techniques without air support (XR 0 NA and XR 30 NA),
the XR 30 A applications resulted in a less uniform spray distribution in the crop. In contrast to the results of our laboratory tests
with a horizontal spray boom (Foqué and Nuyttens, 2011a; Foqué
et al., submitted for publication), air support did not have a positive effect on the spray results in combination with an extended
range flat fan nozzle and a forward spray angle when a vertical
boom was used.
3.3. Effect of spray distance
Fig. 9 presents the results of the ID Venturi flat fan nozzle
(without air support and a standard 0 spray direction) and the
reference technique at two spray distances as both techniques were
tested for a spray distance of 30 cm to the stem (Nuyttens et al.,
2009a; Foqué et al., in press) as well as for a spray distance of
30 cm to the outermost leaves of the canopy (Braekman et al., 2009,
2010; Foqué and Nuyttens, 2011a, 2011b; Nuyttens et al., 2004). For
the ID nozzle, significantly higher depositions were booked for
collector positions Z1 L R un, Z1 L F un, Z1 S B, Z1 S L, Z1 S R, Z1 S F
and Z2 L B un for the 30 cm spray distance to the stem (Fig. 9, ID 120
02 (1)) compared with the 30 cm spray distance to the leaves (Fig. 9,
ID 120 02 (2)). For the XR nozzle type, the 30 cm spray distance to
the leaves only resulted in significantly higher depositions on
collector position Z1 L F up and in significantly lower depositions at
collector positions Z1 L R un, Z1 S R and Z1 S F. On most collector
positions, however, no statistically significant effect of spray
distance on spray deposition for the XR nozzle type was observed.
These results show that a spray distance of 30 cm to the stem
proved to be more effective when spraying conically shaped plants.
Therefore, the fixed spray distance of a vertical spray boom to the
crop should be determined based on the smallest zone of the
canopy. This allows for cultivation of more plants on the same area
without jeopardizing good plant protection.
For this bay laurel crop (Ø 50 cm), some nozzles only passed at
a distance of 5 cm from the outermost edges of the canopy. This
Fig. 9. Results of the factorial ANOVA, based on the square transformed, absolute
deposition dataset of both bay laurel trials with a spray distance of 30 cm to the stem
(1st trial) and a spray distance of 30 cm to the outer crop zone (2nd trial).
A ¼ significant differences in deposition of the extended flat fan nozzle type between
the first (XR 110 03 (1)) and the second trial (XR 110 03 (2)), at the same collector
position. - ¼ significant differences in deposition of the Venturi flat fan nozzle type
between the first (ID 120 02 (1)) and the second trials (ID 120 02 (2)), at the same
collector position. * ¼ depositions that are significantly higher than all the other
unmarked depositions at the same collector position.
85
spray distance seems inadequate for good spray coverage. Literature (Knewitz et al., 2003; Stallinga et al., 2004), however, shows
that using a smaller nozzle spacing enables a reduction in spray
distance. Consequently, the smaller nozzle spacing in Z1 allowed us
to reduce the spray distance. For nozzles with a 110 spray angle,
a nozzle spacing of 12.5 cm results in a theoretically uniform
distribution for such a small spray distance. Smaller spray angles
will result in a more banded spray.
Stallinga et al. (2004) used a smaller nozzle size to keep the
spray volume constant when reducing nozzle spacing. In our trials,
however, the same nozzle type was fitted to all nozzle caps. The
higher spray volume used in Z1 was justified based on the high LAI
in this zone, which was 10 times higher than that used in Z2
(Nuyttens et al., 2009a).
These findings led us to the following hypothesis: as proposed in
literature (Braekman et al., 2009, 2010; Foqué and Nuyttens, 2011a,
2011b; Nuyttens et al., 2004), a vertical boom with a nozzle spacing
of 37.5 cm can be used at a fixed spray distance of about 30 cm to
the outer edges of the canopy for hedge-like crops or plants with
a regular shape (e.g. columnar, cubical or block-shaped). When
spraying plants with a more irregular pruning (e.g. pyramidal,
conical, bonsai or spiral) with a vertical boom, the distance of the
spray boom should be determined relative to the narrowest area in
the shape. A smaller nozzle spacing should be used to provide
a good coverage on places where the canopy gets closer to the
nozzles. In both cases, water-sensitive paper can be used to select
the best combination of nozzle size and settings (Braekman et al.,
2009; Nuyttens et al., 2009a).
In conclusion, from the wide range of tested vertical spray boom
techniques tested, applications with an extended range standard
flat fan nozzle without air support, directed straight toward the
crop generally provided the best spray results in a bay laurel crop
with a fixed spray distance to the stem of about 30 cm. A closer
nozzle spacing is used as it provides the best coverage on leaves
closest to the nozzles. This technique is considered here as the
reference technique.
The Venturi flat fan nozzle provided a valuable alternative for
the extended-range flat fan nozzles. When using the appropriate
spray distance to the crop, this nozzle type often resulted in the
highest deposits and one of the most uniform spray distributions.
The use of an adapted spray direction only proved to add value
using a backward spray direction (30 ) or when an application
with a forward spray direction (30 ) was applied in 2 opposing
successive runs. Although no higher deposits were found than the
ones of the reference technique, both spray applications improved
spray uniformity in the canopy.
The use of air support only resulted in a significant rise in the
overall deposition values for the Venturi flat fan nozzle and a more
uniform spray distribution for the extended range flat fan and the
Venturi flat fan nozzle with the standard spray direction. In
combination with a forward spray direction, the use of air support
increased the differences in deposition between the front and the
back of the plants. In general, air support did not have a positive
effect on the spray deposition values or the penetration of the spray
in the canopy. To improve the effect of air support, the air speed and
volume as well as spray direction should be adapted based on the
crop and spray characteristics.
Acknowledgments
The authors would like to thank the Flemish Government (IWT
Vlaanderen) for financial support. We would also like to acknowledge the Research Center for Ornamental Plants (PCS) and the
members of ILVO’s technical staff for their help on this research.
Special thanks go to Bart Haleydt (PCS) for his assistance during
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D. Foqué et al. / Crop Protection 41 (2012) 77e87
these trials, Miriam Levenson for English-language editing and
Donald Dekeyser for the PDPA laser measurements.
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