<< FIELD TEST >>
PROJET
FINAL REPORT
April 2002

I.C.E. – Délégation Commerciale d’Italie – Tunis
Tél : 00216 / 71940.522 / 71940451 / 71940.458 – Fax : 00216 / 71940.464 / 71940.460
e-mail : tunisi.tunisi@ice.it – site web tunis : http//www.ice.it/estero2/tunisi/default2.htm

SEMINAR SCHEDULE HOTEL HILTON – Tuesday 16 April 2002

9 a.m.: Participants welcomed and registered.

9.30 a.m.: Opening speech by Mr. Alberto CATARCI, Director of the Foreign Trade Institute.
9.45 a.m.: Welcoming speech by the Trade Councillor of the Italian Embassy in Tunis, Mr. Marco
VILLANI.
10 a.m.: Presentation of the project by Mrs. Mirella FINETTI of the External Centre of the
Chambers of Commerce of the Regione Emilia Romagna department.

10.15 a.m.: Main actions of the project by Mr. Elies HAMZA of I.N.A.T.
10.30 a.m.: Mechanization in tree culture by Mr. M. BEN MIMOUN of I.N.A.T.
11 a.m.: First-hand knowledge and affirmations of a producer, Mr. M. MECHICHI.
11.30 a.m.: Coffee break.
11.45 a.m.: Orchard cultivation by Mr. Elies HAMZA of I.N.A.T.
12.15 p.m.: Mechanization in olive growing practices by Mr. H. BEN TAHAR of the Olive
growing Institute.
12.45 p.m.: Mechanization of the oases by Mr. BCHINI of INRAT.
1.15 p.m.: Debate

THE ACTION OF ELECTROSTATIC MIST-BLOWING

I / Introduction

In the majority of pesticide applications, product distribution and its uniformity of coverage are bound to the efficiency of the treatment operation. Thus different methods have been used to evaluate the degree of dusting and the amount of product deposited.
The equipment used for tree culture includes: the “sprinkler”, the “spraying bar”, the “atomizer” and the “mist blower”. The choice of one of these methods depends on certain parameters: the cost of the investment in materials, the structure and size of the farm and the efficacy of the material itself.

At the present time, the most efficient technique is pneumatic mist blowing
whereby a flow of liquid at low speed and low pressure is brought into contact
with a high-speed air flow (>80 m/s). Contact of the air with the liquid causes
the mixture to micronize into droplets. The droplets will become more
homgeneous and their diameter smaller as the air speed becomes faster and
the amount of liquid that passes becomes less. Fine and homogeneous
spraying allows the area covered to be sensibly increased while reducing the
volume of mixture used (from 100 to 200 l/ha) in relation to pressurized
atomizing of the liquid which uses consistent volumes (from 500 to 1500
l/ha).
Pneumatic mist blowing can be equipped with a device for electrostatically
charging the droplets. The droplets are attracted towards the vegetation by
the electrostatic fields that form between the plants, which are optimum
conductors (sap, mineral salts, humidity, etc.) and chemical vapour, carriers
of an electrostatic charge.
Our tests were conducted to compare the action of electrostatic mist blowing
with that of a classic pneumatic mist blowing process, beginning with the
degree to which the droplets of mixture cover the leaves and using the image
analysis method.

II / Materials and methods

Two pneumatic mist blowers, a classic mist blower and an electrostatic mist
blower were tested in an apple tree orchard (fig. 1).
The test conditions were: wind speed 2 m/s, 40% relative humidity and an
ambient temperature of 24°.
The tests were conducted using pieces of water-sensitive paper (2.54 x 2.54
sq.cm) which turned blue when struck by the water droplets, thus giving rise
to the relative coverage rate. The pieces of paper were affixed to the two Tunisia – field test project – final report
sides of the leaves and were then pointed towards the north, south, east,
west and center of the trees.
After the implements had passed and the pieces of water-sensitive paper had
been wetted, they were collected and digitized by means of an A4 colour
scanner whose resolution setting was 600 dpi.
The images were digitized in the red channel at 256 levels of grey. Each pixel
was a square measuring 42 m m each side. The smallest droplet mark
identified measured 50 m m which, using a distribution factor of 2,
corresponded to droplets 25 m m in diameter.

Fig. 1 – Electrostatic mist blowing
Double-suction centrifugal fan
1.5 bar l/h calibrating device with
regulating valves to adapt the jet
to the shape of the tree
Electrostatic diffuser unit

Tunisia – field test project – final report

Fig. 2 : Positions of the pieces of water-sensitive paper on the trees Fig. 2 : Positions of the pieces of water-sensitive paper on the trees
III / Results

A four square centimeter area of digitized image was treated. It was filtered
to increase the contrast between the droplets and the background. Selection
was limited to a level of grey so as to obtain an image where the pixels were
black or white, depending on whether their level of grey was above or below
the established threshold. The droplets of the original image were thus
isolated on a white background. Using this image, the “Image Tool” logic was
able to identify objects or droplet marks.

The coverage rate results (Fig. 3) show that electrostatic mist blowing
obtained higher coverage rates than the classic pneumatic mist blowing in all
cases. An analysis of the variant of the two treatments showed that
electrostatic mist blowing was more homogeneous than classic pneumatic
mist blowing.

Tunisia – field test project – final report

Coverage rate %

An analysis of the pieces of water-sensitive paper positioned on the trees
and on the ground showed that unlike the classic mist blowing process, the
pieces of paper failed to turn blue in the case of electrostatic mist blowing.
This confirmed electrostatic mist blowing’s total absence of loss through
drifting and flowing.

Fig. 3 : Histogram of the rate of coverage obtained from the two mist blowing
processes
0
5
10
15
20
25
30
1 2 3 totale
Mist blowing Electrostatic
Tunisia – field test project – final report

ACQUISITION OF THE IMAGE FOLDER

The pieces of water-sensitive paper are digitized by means of a scanner.
The “images” folders are processed by an “Image Tool” image analysing software.
The image is filtered to increase the contrast between the drops and background.
The threshold of the image is established at a fixed level of grey so as to binarize it.
The drop marks are identified and the elongation, area and coverage rate parameters calculated.