Exploring variable air flow rate as a function of leaf area index for optimal spray deposition in trellised vineyards

Abstract

In 3D crops, excessive fan airflow speed may reduce deposition and increase spray losses due to canopy compression. To solve this problem, variable fan airflow rate as a function of canopy characteristics is a key in the context of a sustainable crop protection technology. The effects on spray canopy deposition of different air volume rates (low, medium, and high) generated by a 700 mm diameter axial fan, combined with 4 and 8 km h-1 forward speed, were assessed in a vineyard at an early and late growth stage. The objective was to identify the fan airflow setting (m3 h-1) which maximizes canopy spray deposition (% of applied) with the final aim to determine the relationship between leaf area index (LAI) and optimal fan airflow rate. The results confirmed that an excessive airflow rate significantly decreases spray deposits. When the forward speed increased from 4 to 8 km h-1, the airflow rate had to be increased from low to medium to maximize canopy spray deposition. The results showed the importance of total air volume applied per hectare (m3 ha-1) as a parameter to maximize the spray deposits, irrespective of forward speed. Finally, the relationship between the LAI (adim.), accounting for crop characteristics and canopy density, and the total air volume applied (m3 ha-1) to maximize the canopy spray deposition was identified.

Full text

Aspects of Applied Biology 147, 2022
International Advances in Pesticide Application
251
Exploring variable air ow rate as a function of leaf area index for
optimal spray deposition in trellised vineyards
By M GRELLA1, F GIOELLI1, P MARUCCO1, E MOZZANINI1, A CAFFINI2,
D NUYTTENS3, I ZWERTVAEGHER3, S FOUNTAS4, L ATHANASAKOS4, N MYLONAS4
and P BALSARI1
1Department of Agricultural, Forest and Food Sciences (DiSAFA), University of Turin
(UNITO), Turin, Italy
2CAFFINI S.p.a., Palù, Italy
3Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Merelbeke, Belgium
4Agricultural University of Athens (AUA), Athens, Greece
Corresponding Author Email: marco.grella@unito.it
Summary
In 3D crops, excessive fan airow speed may reduce deposition and increase spray losses
due to canopy compression. To solve this problem, variable fan airow rate as a function
of canopy characteristics is a key in the context of a sustainable crop protection technology.
The eects on spray canopy deposition of dierent air volume rates (low, medium, and high)
generated by a 700 mm diameter axial fan, combined with 4 and 8 km h-1 forward speed,
were assessed in a vineyard at an early and late growth stage. The objective was to identify
the fan airow setting (m3 h-1) which maximizes canopy spray deposition (% of applied)
with the nal aim to determine the relationship between leaf area index (LAI) and optimal
fan airow rate. The results conrmed that an excessive airow rate signicantly decreases
spray deposits. When the forward speed increased from 4 to 8 km h-1, the airow rate had to
be increased from low to medium to maximize canopy spray deposition. The results showed
the importance of total air volume applied per hectare (m3 ha-1) as a parameter to maximize
the spray deposits, irrespective of forward speed. Finally, the relationship between the LAI
(adim.), accounting for crop characteristics and canopy density, and the total air volume
applied (m3 ha-1) to maximize the canopy spray deposition was identied.
Key words: Precision agriculture, variable airow rate, electrically driven axial fan, spray
canopy deposit, airblast sprayer
Introduction
The adjustment of the air jet (fan airow rate, velocity and, if possible, direction) in vineyard
sprayers in function of the canopy morphology (size, leaf density and row distance) can avoid
areas with under- or over-application of plant protection products (PPP) and can reduce losses
due to spray drift. Vines of the same variety can strongly vary in shape, size, and foliage density
within the same parcel and among plots. A precise and continuous air jet adjustment according to
the crop characteristics within the vineyard is thus key for an ecient and sustainable pesticide
application. In general, the fan airow aims to carry the PPP droplets onto the target and move the
foliage in order to improve the deposition on the internal part of the canopy and on the underside

252
of the leaves. Nevertheless, it is well known for 3D crops that an excessive air support may reduce
deposition, owing to canopy compression, and increase spray losses (Hislop, 1991; Balsari &
Marucco, 2004). For example, Pergher (2005) reported that a reduction of the air ow rate from
10.6 to 6.3 m3 s-1 increased mean foliar deposits by 25–30% in a vineyard. Therefore, the possibility
to vary fan airow as a function of canopy characteristics, especially density, is key in the context
of a sustainable crop protection technology.
Current technical solutions generally foresee the use of mechanically driven fans with dierent
revolution speed using a gearbox and/or lowering the Power Take O (PTO) of the tractor. Another
solution consists of reducing the fan air suction section by a diaphragm. In recent years, more
advanced sprayers with adjustable fan settings, which are able to vary continuously and in real
time the airow characteristics, have been developed. These sprayers are either equipped with
several axial fans mounted in dierent positions on the sprayer or can change the width of the fan
air outlet channel and/or the blades pitch, etc. (García-Ramos et al., 2012; Endalew et al., 2010;
Hołownicki et al., 2017; Salcedo et al., 2021). However, for all these solutions, the possibility to
vary airow settings continuously and automatically along the rows is limited.
While dierent methodologies have been established to determine the optimal spray application
rate depending on the canopy characteristics (Llorens et al., 2010; Garcerà et al., 2017), few data
exist concerning the relationship between airow characteristics and canopy morphology (size
and density). Instruction manuals (TOPPS, 2014), digital tools (Doruchowski et al., 2013), and
devices (Bahlol et al., 2020) that allow to roughly adjust the airow characteristics to the target
have been developed. However, such tools require a manual fan setting which cannot be done for
each specic canopy morphology and, in most cases, the airow adjustment is totally left to the
operator’s skills and experience.
Therefore, within the H2020-OPTIMA project (OPTimised Integrated Pest Management for
precise detection and control of plant diseases in perennial crops and open-eld vegetables,
www.optima-h2020.eu), a cost-eective integrated system, enabling to vary the fan revolution
speed automatically and continuously according to the canopy density, was designed (Grella et
al., 2022). Canopy density values are obtained from one ultrasonic sensor per sprayer side and
are processed through an algorithm in a controller. Based on the output from the algorithm, the
controller communicates the required fan revolution speed to the fan inverter. This algorithm is based
on the relationship between canopy characteristics and fan airow rate and has to be determined
experimentally.
The objective of this experimental work was i) to determine the optimal airow rate to be set
in a trellised vineyard to maximize canopy spray deposit for dierent canopy morphologies and
forward speeds, and ii) to investigate the feasibility of leaf area index (LAI) as a parameter for
dening the optimal fan setting.
Materials and Methods
Test location and vineyard characterization
Field trials were carried out at DiSAFA facilities (Grugliasco, Italy) in an experimental espalier-
trained vineyard (cv: Barbera) at two growth stages, namely early (BBCH 57, inorescences fully
developed; owers separating) and late (BBCH 89, berries ripe for harvest). The vine rows were
62 m long and oriented NW–SE (146° azimuth). Planting distances were 2.8 m between rows and
0.8 m within rows, resulting in a density of 4,464 vines ha-1. The inclined point quadrat technique
(PQT) was applied to accurately characterize the vineyard crop before the trials (Grella et al.,
2019). PQT measurements were taken in the vegetative strip of six vines coincident with those
used for canopy deposition sampling described in the following section (Experimental plot layout
and sampling system). The mean vegetative parameters, namely leaf layers and gaps, were thus
obtained, and leaf area index (LAI) was calculated from Eq. (1) according to Vitali et al. (2013):

253
LAI = Ly*(Hc/Rd) (1)
where LAI is leaf area index (adim.); Ly is the average number of leaf layers (n°); Hc is the canopy
height (m); Rd is the inter row distance (m).
An overview of the vegetative characteristics of the vines used for experimental sampling is
presented in Table 1. The average number of leaf layers was 0.77 and 2.31, the average of gaps was
60 and 14 %, and LAI was 0.33 and 1.33 (adim.), respectively for the early and late growth stage.
Table 1. Vegetative characteristics of the vines used for sampling at early and late growth stage
Growth
stage BBCH Depth (m) Height (m) N° of leaf
layers Gap (%) LAI
(adim.)
Early 57 0.39 1.06 0.82 61 0.35
Early 57 0.31 1.05 0.75 61 0.32
Early 57 0.38 0.89 0.81 58 0.29
Early 57 0.44 1.18 0.79 57 0.37
Early 57 0.38 1.07 0.72 60 0.31
Early 57 0.46 1.20 0.75 63 0.36
Late 89 0.42 1.65 2.13 19 1.25
Late 89 0.50 1.61 2.39 13 1.37
Late 89 0.44 1.55 2.11 18 1.17
Late 89 0.62 1.59 2.25 11 1.28
Late 89 0.42 1.62 2.31 17 1.34
Late 89 0.54 1.66 2.67 6 1.58
Sprayer characteristics and congurations tested in eld trials
A prototype vineyard sprayer, i.e. Smart Synthesis (Cani S.p.a., Palù, Verona, Italy), was
employed. It is a trailed sprayer with a 1,000 L polyethylene tank and an innovative electrically
driven axial fan (KEB automation KG, Barntrup, Germany) (Fig. 1a). The fan, 700 mm in diameter
and consisting of nine blades, sucks in the air from the front of a tower shaped air conveyor. The
latter is equipped with multiple adjustable deectors placed internally at the edge of the air-jet outlet,
thus allowing to direct the airow to precisely match the canopy height. An electric-control varies
the orientation of the whole air conveyor with respect to the central axis of the air-jet discharge
system backwards and forward, thus determining the incidence angle of both airow and spray jets
on the canopy. Furthermore, the sprayer was equipped with a DynaJet® Flex 7140 Pulse Width
Modulation (PWM) system (TeeJet, Spraying Systems Co., Wheaton, Illinois, USA) featured by
eight PWM solenoid valves coupled with a single nozzle holder per sprayer side (Fig. 1b). The
PWM valves can vary the duty cycle of the pulse signals continuously from 30 to 100% to change
the spray outputs but were only used at 100% DC in this study. Further details are provided in
Grella et al. (2021, 2022) and Zwertvaegher et al. (2022).
Using the electrically driven axial fan, dierent fan revolution speeds were set to test the eect
of fan airow rate (m3 h-1) on canopy deposition at the two growth stages. Three levels of airow
rate (low, medium, and high) were arbitrarily selected for tests. The fan revolution speeds at each
level varied according to the growth stage (as the canopy density increased) from 400 to 1,000
rev min-1 for the early growth stage, and from 700 to 1,750 rev min-1 for the late growth stage
(Table 2). The electric axial fan ensured the desired fan revolution speed, irrespective of the PTO
revolution speed, throughout the trials. In addition, two sprayer forward speeds (4 and 8 km h-1)
were combined with selected fan settings, at both growth stages, to test their eect on the canopy
deposition and possible interactions with airow rate (Table 2).

254
Fig. 1. Prototype vineyard sprayer equipped with electrically driven fan and PWM spray system during eld
trials at a) early (lateral sprayer view) and b) late (back sprayer view) growth stages.
Table 2. Overview of electrically driven axial fan settings tested in eld trials at early and late
growth stage in combination with two forward speeds for their eect on canopy deposition
Growth
stage
Forward speed
(km h-1)
Airow
setting
Fan speed
(rev min-1)
Airow rate
(m3 h-1)
Total air volume
applied (m3 ha-1)
Early 4.0 Low 400 4,728 4,225
Early 4.0 Medium 700 8,378 7,488
Early 4.0 High 1,000 11,876 10,614
Early 8.0 Low 400 4,728 2,113
Early 8.0 Medium 700 8,378 3,744
Early 8.0 High 1,000 11,876 5,307
Late 4.0 Low 700 8,378 7,488
Late 4.0 Medium 1,300 15,398 13,762
Late 4.0 High 1,750 20,663 18,468
Late 8.0 Low 700 8,378 3,744
Late 8.0 Medium 1,300 15,398 6,881
Late 8.0 High 1,750 20,663 9,234
The sprayer was equipped with eight standard at fan nozzles XR 80 02 VS (TeeJet, Spraying
Systems Co., Wheaton, Illinois USA) per sprayer side. All trials were carried out at a xed working
pressure of 0.40 MPa and 100% PWM duty cycle, providing an individual nozzle ow rate of 0.91
L min− 1. Based on a preliminary check of the vertical spray prole, only four and six nozzles per
sprayer side were activated at the early and late growth stage, respectively. Irrespective of growth
stage, the bottom nozzle was turned o on both sides while at the top three and one nozzles were
turned o at early and late growth stage, respectively. Resulting spray volumes were 390 and 195
L ha-1 at early growth stage and 585 and 293 L ha-1 at late growth stage for 4 and 8 km h-1 forward
speed, respectively.
In all cases the internal air deectors were adequately adjusted to match the canopy height and to
minimize spray losses over the canopy. The air conveyor was placed orthogonal to the rows (90°
relative to the central axis of the air-jet discharge system) in all trials.
Experimental plot layout and sampling system
The trials were performed by spraying the two outermost vineyard rows, with a total area of 347
m2 (62.0 m × 5.6 m) (Fig. 2a). Canopy spray deposition measurements were performed at three

255
locations along the sprayed rows, corresponding to three vine canopies per sprayed row. In total,
measurements were taken from six vines, as shown in Fig. 2a. At the early growth stage, spray
deposition was assessed at four sampling positions, i.e. at two heights (1 and 2) and two depths (A
and C) (Fig. 2b), while at the late growth stage nine sampling positions were assessed, i.e. three
heights (1, 2, and 3) and three depths (A, B, and C) (Fig. 2c). To assess the deposition, round lter
papers (120 mm diameter and 90 g m-2 extra rapid, Gruppo Cordenons S.p.A., Milan, Italy) were
clipped to vertical masts at each sampling position. Each collector represented a total exposed
surface area of 226 cm2. At the end of each spray application, samples were left to dry for 10 min,
placed into individual bags and sealed. To prevent tracer photo-degradation, the samples were
collected in closed dark boxes. Each test was repeated three times.
Fig. 2. Schematics of a) trial layout for the measurement of canopy deposition (aerial view) and related
sampling strategy at early b) and c) late growth stages; canopy depths A, B, and C, and canopy heights 1,
2, and 3.
Sprayed mixture and laboratory analysis
To measure the collector spray deposits, E-102 Tartrazine yellow dye tracer was added to the
sprayer tank at a target concentration of about 10 g L−1. Before and after each spray application, the
tank mixture was sampled directly from the nozzles to determine the precise tracer concentration
of each repetition.
The collectors were washed with deionized water to extract the tracer. The Tartrazine concentration
was determined by measuring the absorbance of the washing solution with a spectrophotometer
UV-1600PC (VWR, Radnor, PA, USA) set to 427 nm wavelength for peak absorption of the dye
and comparing it to the calibration curve obtained in the laboratory prior to the analysis. In all
cases, three absorbance measurements were taken from each sample.
The deposit on each collector (Di), expressed per unit area in μL cm−2, was calculated from Eq.
(2) as follows:
where Di is the spray deposit on a single collector (μL cm−2); psmpl is the absorbance value of the
sample (adim.); pblk is the absorbance of the blanks (adim.); Vdil is the volume of the deionized
water used to extract tracer deposit from the collector (μL); pspray is the absorbance value of the
spray mixture concentration applied during testing and sampled at the nozzle outlet (adim.); Acol
is the projected area of the collector exposed to the spray (cm2).
For a broad comparison of data, the spray deposit values (μL cm-2) were transformed to be expressed
as % of applied volume.
Di = ((psmpl - pblk) * Vdil) / (pspray * Acol) (2)

256
Data processing and statistical analysis
All statistical analyses were performed using IBM SPSS Statistics (Version 27) predictive
analytics software for Windows®. To investigate at what sprayer setting combinations the highest
spray depositions were obtained, a three-way ANOVA was performed with growth stage (early
vs late), airow rate (low vs medium vs high) and forward speed (4 vs 8 km h-1) as independent
variables and canopy deposition (% of applied volume) as dependent variable. The interactions
among independent variables were also investigated. To investigate the dierences among spray
deposition obtained at dierent airow settings, the means were compared using a Duncan post-
hoc test for multiple comparison (P < 0.05). The fan settings able to maximize the canopy spray
deposits at dierent forward speeds at late and early growth stage were then objectively identied.
A one-way ANOVA was carried out to investigate the eect of forward speed (4 vs 8 km h-1) on
spray canopy deposit obtained just from the fan settings able to maximize the canopy deposition.
Results and Discussion
The three-way ANOVA (Table 3) indicates that growth stage exerted a statistical inuence on
the canopy deposition (% of applied volume) irrespective of fan airow setting and forward speed
adopted.
Table 3. Results of the three-way ANOVA for the canopy deposition (% of applied volume)
Sources DF P > (F) Signicance a
Main eects
Growth stage (GS) 1 3.24E-22 ***
Fan airow setting (ARF) b21.39E-07 ***
Forward speed (FWS) 10.393 NS
Interactions
GS × AFR 20.969 NS
GS × FWS 1 0.447 NS
AFR × FWS 2 1.01E-04 ***
GS × AFR × FWS 2 0.576 NS
a Statistical signicance level: NS P > 0.05; * P < 0.05; ** P < 0.01; *** P < 0.001,
b Fan airow rate corresponds to Low, Medium and High levels.
Average canopy depositions expressed as % of applied volume were 38.5% . 25.5% for early
and late growth stages, respectively. The huge increase in canopy density along the growing
season resulted in a decrease in average deposition, as the inner parts of the row are much more
dicult to reach. In addition, airow setting signicantly aected canopy deposition (Table 3), as
it varied the airow rate (m3 h-1) (Table 2). The higher the fan airow rate, the lower the canopy
deposition irrespective of growth stage (33.4% low, 32.5% medium and 25.9% high). A signicant
interaction was found between air ow setting and forward speed, meaning that eect of forward
speed depended on air ow setting (as can be seen in Fig 3). Fig. 3 displays the average canopy
spray deposition obtained for dierent air ow setting forward speeds and growth stages. At 4
km h-1, the adoption of a low fan speed (400 and 700 rev min-1 at early and late growth stages,
respectively) allowed to obtain a signicant increase in spray deposition compared to the other
fan speeds. At 8 km h-1, the highest spray depositions were obtained with the medium fan speed
(1,000 and 1,300 rev min-1 at early and late growth stages, respectively). The medium fan speed
resulted in a signicantly higher deposition than the low and high fan speed at the early growth

257
stage, but at the late growth stage only the dierence with the high fan speed was signicant. The
results are in line with those found by other authors reporting a decrease in canopy deposition due
to an excessive airow rate generated by axial fan sprayer (Pergher, 2005; Balsari & Marucco,
2004). However, at 8 km h-1 the low fan speed probably did not provide enough airow to open
and move the dense (late stage) canopy, resulting in a reduced spray penetration and lower spray
deposition value. When increasing forward speed, the airow rate must be increased in order to
maximize spray deposition at both growth stages.
Fig. 3. Average canopy deposition (% of applied volume) for the dierent fan speed setting (low, medium,
high) at 4 and 8 km h-1 forward speed and at early and late growth stage. The bars show the mean ± standard
error of the mean. Dierent letters on the bars denote signicant dierences within forward speed and growth
stage (Duncan’s post hoc test, P < 0.05).
Focusing solely on the fan settings able to maximize the canopy deposition, the one-way ANOVA
underlines that there is no signicant eect of forward speed (4 vs 8 km h-1) on canopy deposition
[F(1, 1) = 0.697, P = 0.406]. This is because an adequate level of air volume per ground area (m3
ha-1) was maintained through changes in fan revolution speed setting. Indeed, at early growth stage,
increasing forward speed from 4 to 8 km h-1 did not signicantly aect spray deposition because
the fan speed was increased from low (400 rev min-1) to medium (700 rev min-1) resulting in similar
amounts of total air volume applied, i.e. 4,225 vs 3,744 m3 ha-1 (Table 2). Similar results were found
at the late growth stage with highest spray deposition values for total air volumes applied of 7,488
m3 ha-1 (4 km h-1 and low fan speed - 700 rev min-1) and 6,881 m3 ha-1 (8 km h-1 and medium fan
speed – 1,300 rev min-1) (Table 2). It indicates that within each growth stage, canopy spray deposition
can be maximized by applying an adequate total air volume per ground area (m3 ha-1) through the
correct combination of fan revolution speed and forward speed. Total air volume applied was thus
demonstrated to be the main factor to take into account to maximize the canopy spray deposition.
Based on this nding, a linear t model was obtained to describe the relationship between the LAI
(Table 1) and the corresponding optimal air volume applied (m3 ha-1) to maximize canopy spray
deposition (Fig. 4). The model thus provides values for the total air volume to be applied at the
dierent growth stages. A threshold LAI value of 2.5 (represented by the red line perpendicular on
the x axis in Fig. 5) was set because in modern commercial trellised vineyards leaf layers is kept

258
below 2.5 through adequate canopy management techniques, such as shoot trimming, positioning,
and tying (Intrieri & Poni, 1995). As an example, a LAI value of 2.45 can be achieved by a trellised
vineyard with “extreme” features, i.e. 2.2 m inter-row distance, vegetative strip of 1.8 m width,
canopy depth of 0.8 m and mean leaf layer equal 3.0. Based on the linear model, the corresponding
optimal value for the total air volume would be 10,735 m3 ha-1. At 4 km h-1 forward speed, this
corresponds with a fan speed setting of about 1,000 rev min-1, or slightly higher (Table 2). At 8 km
h-1 forward speed, fan settings higher than those tested in this experiment (1,750 rev min-1) would
be needed.
Fig. 4. Linear t model describing the relationships between the Leaf Area Index (LAI, adim.) and the total
air volume applied (m3 ha-1) based on experimental data obtained in the tests at 4 and 8 km h-1 forward speeds.
The red lines represent a maximum threshold LAI value in modern vineyards that denes the maximum
total air volume to be applied (10,735 m3 h-1) in vineyard spray application.
Conclusions
The results obtained from this preliminary, experimental work are the basis for the development of
a smart sprayer equipped with an electrically driven axial fan able to provide an optimized variable
airow rate based on a real-time measurements of canopy characteristics. This study explores the
possibility to use the LAI as a parameter for setting the optimal fan speed (rev min-1) automatically
in order to deliver the desired total air volume applied (m3 ha-1). Further relationships among other
available canopy parameters (i.e. number of leaf layers, % of gaps, tree row volume, and leaf wall
area) and total air volume applied per ground area (m3 ha-1) are under investigation in order to
dene the most useful canopy parameter for selecting the optimal fan setting. Additional trials are
ongoing to evaluate the eect of a wider range of fan revolution and forward speed settings on
canopy spray deposition.
Acknowledgements
This project has been funded by the European Union’s Horizon 2020 research and innovation
program under grant agreement No 773718 (OPTIMA-project). Special thanks go to KEB ITALIA
S.r.l. for providing technical support, and to Marco Resecco for the help provided during eld
experimental activities.

259
References
Bahlol H Y, Chandel A K, Hoheisel G-A, Khot L R. 2020. The smart spray analytical system:
developing understanding of output air-assist and spray patterns from orchard sprayers. Crop
Protection 127:104977. https://doi.org/10.1016/j.cropro.2019.104977.
Balsari P, Marucco P. 2004. Sprayer adjustment and vine canopy parameters aecting spray drift:
the Italian experience. In Proceedings of the International Conference on Pesticide Application for
Drift Management, pp. 109–115. Waikoloa, Hawaii, 27–29 October 2004.
Doruchowski G, Balsari P, Gil E, Marucco P, Roettele M, Wehmann H-J. 2014. Environmentally
Optimised Sprayer (EOS)-A software application for comprehensive assessment of environmental
safety features of sprayers. Science of the Total Environment 482–483:201–207. https://doi.
org/10.1016/j.scitotenv.2014.02.112.
Endalew A M, Debaer C, Rutten N, Vercammen J, Delele M A, Ramon H, Nicolaï B M,
Verboven P. 2010. A new integrated CFD modelling approach towards air assisted orchard
spraying. Part II. Validation for dierent sprayer types. Computers and Electronics in Agriculture
71(2):137–147. https://doi.org/10.1016/j.compag.2009.11.005.
Garcerà C, Fonte A, Moltò E, Chueca P. 2017. Sustainable use of pesticide applications in citrus:
a support tool for volume rate adjustment. International Journal of Environmental Research and
Public Health 14(7):715. https://doi.org/10.3390/ijerph14070715.
García-Ramos F J, Vidal M, Boné A, Malòn H, Aguirre J. 2012. Analysis of the airow generated
by an air-assisted sprayer equipped with two axial fans using a 3D sonic anemometer. Sensors
12(6):7598–7613. https://doi.org/10.3390/s120607598.
Grella M, Marucco P, Balsari P. 2019. Toward a new method to classify the airblast sprayers
according to their potential drift reduction: comparison of direct and new indirect measurement
methods. Pest Management Science 75:2219–2235. https://doi.org/10.1002/ps.5354.
Grella M, Gioelli F, Marucco P, Zwertvaegher I, Mozzanini E, Mylonas N, Nuyttens D, Balsari
P. 2021. Field assessment of a pulse width modulation spray system applying dierent spray
volumes: duty cycle and forward speed eects on vines spray coverage. Precision Agriculture,
23:219–252. DOI 10.1007/s11119-021-09835-6.
Grella M, Marucco P, Athanasakos L, Mylonas N, Gioelli F, Zwertvaegher I, Cani A, Meroni
F, Rossi R, Nuyttens D, Fountas S, Balsari P. 2022. Airblast sprayer electrication for real-time,
continuous fan-airow adjustment according to canopy density during pesticide application in 3D
crops. LAND.TECHNIK 2022 - The Forum for Agricultural Engineering 2395:389–395.
Hislop E C. 1991. Air-assisted crop spraying: an introductory review. In Proceedings of the BCPC
Symposium on Air-assisted Spraying in Crop Protection, pp. 3–14. Swansea, UK, 7–9 January 1991.
Hołownicki R, Doruchowski G, Swiechowski W, Godyn A, Konopacki PJ. 2017. Variable
air assistance system for orchard sprayers; concept, design and preliminary testing. Biosystems
Engineering 163:134–149. https://doi.org/10.1016/j.biosystemseng.2017.09.004.
Intrieri C, Poni S. 1995. Integrated evolution of trellis training systems and machines to improve
grape quality and vintage quality of mechanized Italian vineyards. American Journal of Enology
and Viticulture 46:116–127.
Llorens J, Gil E, Llop J, Escolà A. 2010. Variable rate dosing in precision viticulture: use of
electronic devices to improve application eciency. Crop Protection 29(3):239–248.
Pergher G. 2005. Improving vineyard sprayer calibration – air ow rate and forward speed. Annual
Review of Agricultural Engineering 4(1):197–204.
Salcedo R, Fonte A, Grella M, Garcera C, Chueca P. 2021.Blade pitch and air-outlet width eects
on the airow generated by an airblast sprayer with wireless remote-controlled axial fan. Computers
and Electronics in Agriculture 190:106428. https://doi.org/10.1016/j.compag.2021.106428.
TOPPS-Prowadis Project. 2014. Best management practices to reduce spray drift. Available at
http://www.topps-life.org/ [accessed November 2021].

260
Vitali M, Tamagnone M, La Iacona T, Lovisolo C. 2013. Measurement of grapevine canopy
leaf area by using an ultrasonic-based method. Journal International des Sciences de la Vigne et
du Vin 47(3):183–189.
Zwertvaegher I, Fountas S, Mylonas N, Athanasakos L, Balsari P, Grella M, Marucco P,
Cani A, Nuyttens D. 2022. Pulse width modulation: eect of duty cycle on nozzle ow rate
and droplet characteristics. Aspects of Applied Biology 147, International Advances in Pesticide
Application, pp. 47–54.