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

84 Sally A. Bound
switch of heather to flick copper-lime mixtures over foliage. According to Heijne
(1980) the first pump operated sprayer was built in France in 1885, and in 1888 a
geared spraying machine was commercially available. Morgan (1992) suggests
that the construction of machines specifically for spraying began in 1886 with ‘hand
operated rotating brushes, bellows air atomisers and hydraulic back pack sprayers
whose design has not altered to this day’.
The design of early hydraulic nozzles was simple, with the liquid being restricted
as it approached the outlet orifice. Rapid development led to three basic nozzle
designs. The fan nozzle, in which the liquid stream was modified by the shape of
the outlet orifice, was followed by the development of the impact nozzle where
the liquid stream was modified by an obstruction after the outlet orifice. Towards
the end of the 19th century, Riley designed the swirl or cone nozzle in which a rotary
motion was applied to the liquid stream causing it to break up immediately after
leaving the outlet orifice (Morgan, 1992). This nozzle is still one of the main
atomising devices used in tree crop spraying.
Initially there was little information available on the range of liquid volumes
or the type of spray distribution required to produce the desired biological effect.
In the early 1900’s sprays were applied by hand-directed nozzles and a ‘fine spray’
was recommended. In order to spray tall trees, hand-directed nozzles had to be
carried on long tubes supplied through flexible hoses. To avoid the need for long
hoses, horse drawn wheeled machines were utilised, some with tall platforms to
enable operators to reach the tops of trees. The 1930’s saw the introduction of
adjustable spray guns which enabled a skilled operator to use large spray drops
with sufficient momentum to reach the tops of trees or smaller drops in wider sprays
for the lower branches. Up to the second world war, mainly contact pesticides
were used and many deficiencies in pest and disease control could be ascribed to
failure to reach all or most of the target organisms with the spray liquid (Morgan,
1992). Although slow and laborious, in skilled hands the manual lance or gun
applications were very effective because of their ability to cope with variations in
tree geometry and multi-directional spraying.
In the immediate post war period, ‘automatic’ spraying methods were introduced
with the fixing of hydraulic swirl nozzle assemblies on tractor-drawn
machines. These were mounted at the rear of the machine on either low frames or
on tall masts the same height as the trees, and were driven by a separate motor or
via a power take-off shaft from the tractor. The most long lasting post-war development
in tree spraying was air-blast application, first introduced on a large scale
in the USA (Morgan, 1992). This meant that the projection of the spray to the
trees was no longer dependent on the momentum of the droplets themselves but
on their passive transport in a powerful airstream from a motor-driven fan. The
first patent for the air-blast principle was granted in 1944, for the ‘Speed Sprayer’
(Feutrill, 1998). The traditional air-blast sprayer consists of a conventional axial
fan fitted with hydraulic nozzles, mounted behind a large wheeled spray vat. As a
result of this development, droplets could be much smaller as they no longer
needed much momentum, and the same or greater number of droplets could be
produced from a smaller volume of liquid. By halving the droplet diameter the
same number of drops can be produced from one eighth of the liquid volume.