Production Practices and Quality Assessment of Food Crops. Vol. 1

100 Sally A. Bound
coverage and coverage uniformity. Lovelidge (1993) suggests that the air-blast
sprayer has outlived its value, stating that its use of a high volume of fast moving
air to carry chemicals to the target is excessive for modern orchards and is becoming
environmentally and financially unacceptable because much of the spray misses
the target. The problem is finding an effective and acceptable alternative. The fitting
of ducting to air outlets has allowed more accurate spraying but because the air-blast
principle has been retained these sprayers still lose a significant proportion of
spray. ULV sprayers have enabled significant reductions in chemical use, however
with the spray still carried by a large volume of high speed air as much as 80%
misses the target (Lovelidge, 1993).
One of the first machines to produce slow moving air was trialed in the UK in
1992 (Lovelidge, 1993). Air is directed along six 15 cm diameter flexible plastic
ducts (three each side), each fitted with a Micron nozzle at the outlet. To ensure
maximum spray coverage, the position and direction of the outlets are adjustable.
This placement sprayer wasted less spray than standard ULV machines.
The Hydra sprayer, developed in Australia (Furness, 1997), produces a large
volume of highly turbulent air at relatively low velocity by axial rotation generated
by the fan combined with airstream convergence from adjacent heads. Hollow
cone nozzles are located behind the fan and the spray is ducted through the fan.
As the spray cloud is directed through the fan it is subjected to high airshear forces
near the surface of the fan blades, producing a secondary atomisation resulting in
fine 100 µm droplets. Spray coverage is even with a dense spray deposit on 80–100%
of upper leaf surfaces and on 70–95% of lower leaf surfaces on both outer and
inner canopy. This system is now widely used in the grape industry in Australia
and has reduced spraying costs, improved fruit quality and improved pest and disease
control.
7. CONCLUSIONS
There has been phenomenal progress in spray technology over the last 30 years.
An increased awareness of the issues relating to spray efficiency has led researchers
to re-examine factors such as air velocity and pattern, nozzle placement in relation
to the crop, and methods of reducing chemical dosage rates. Advances have been
made in understanding many of the factors involved in spray efficiency, such as
droplet size, coverage, penetration and retention, and machine design.
The increasing prominence of environmental issues combined with the spread
of urban areas has forced orchardists to alter their practices in relation to spray
application. With the move away from complete coverage of the trees with high
volume spraying towards low or ultra-low volume technology, there has been a
reduction in drift and runoff, reducing the amount of pollution and wastage. While
this has benefited both orchardist and the public, truly efficient spray application
systems cannot be developed until there is a full understanding of the interactions
of all the components affecting the efficiency of sprays applied to tree crops,
Educating orchardists to apply the TRV system as outlined by Manktelow and
Praat (1997b) or the UCR concept described by Furness et al. (1998) will assist