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

SPRAY TECHNOLOGY IN PERENNIAL TREE CROPS
SALLY A. BOUND
Tasmanian Institute of Agricultural Research, 13 St John’s Avenue, New Town, Tasmania 7008, Australia
1. INTRODUCTION
In order to optimise pesticide use, an understanding of the principles and practices
of crop spraying and pesticide application is required. Lodeman (1896, cited
in Heijne, 1980) defined spraying as ‘the throwing upon plants of any fluid or
semi-fluid in the form of fine rain or mist’. Over a century later, with an increased
awareness of the impact of pesticides, Manktelow (2000) has described successful
spraying as the application of appropriate chemicals, at appropriate times and
rates, to produce adequate coverage of the target canopy with an effective chemical
dose.
Until relatively recently, spray application technology on perennial tree crops was
poorly researched. Changes in manufacturing technology have improved sprayer
design, but the general concepts of spraying that were introduced at the end of
the nineteenth century are still being applied today. The requirement for effective
spraying in perennial tree crops is for the chemical to be applied evenly throughout
the tree, so that the active ingredient reaches the target. Failure to achieve this results
in poor pest/disease control or ineffective uptake of plant bioregulators (PBRs),
and usually the chemical is claimed to be ineffective or the argument of pest resistance
arises. To avoid this situation, operators need to be aware of the issues involved
in relation to both tree and sprayer.
In recent years, many countries have begun to adopt practices to reduce spray
pollution from drift and runoff, particularly with the increasing urban encroachment
on orchards. Addressing this issue through improved spraying performance
and more efficient targeting has not only resulted in reduced chemical usage, but
also in a significant reduction in pollution and wastage, benefiting both orchardists
and the public at large.
This chapter discusses the development of spray technology in perennial tree
crops. Mechanisms of droplet production and factors influencing the efficiency of
spraying are discussed in addition to the technological developments that have led
to improvements in spray application. While mentioned in passing, the impact of
tree and climatic factors is not discussed in depth.
2. THE DEVELOPMENT OF SPRAY TECHNOLOGY
Prior to the 1880’s, liquids were applied to plants with watering cans and syringes.
The first reports of spraying in perennial crops date back to 1850 when a syringe
was used to apply an aqueous solution of flowers of sulphur to grape vines to control
powdery mildew (Morgan, 1992). In 1882, Millardet recommended the use of a
R. Dris and S. M. Jain (eds.), Production Practices and Quality Assessment of Food Crops,
Vol. 1, Preharvest Practice”, pp. 83–104.
© 2004 Kluwer Academic Publishers. Printed in the Netherlands.
83