Jv. Cross et al., Spray deposits and losses in different sized apple trees from an axial fanorchard sprayer: 2. Effects of spray quality, CROP PROT, 20(4), 2001, pp. 333-343
Two field experiments compared spray deposits and losses from very fine (vo
lume median diameter (VMD) = 156 mum), fine (VMD = 198 mum) and medium (VMD
= 237 mum) quality spray applications to young dwarf, dwarf and semi-dwarf
apple trees From an axial fan orchard sprayer fitted with hydraulic hollow
cone nozzles. All other spray application variables were kept constant. In
one experiment, the very fine quality treatment deposited slightly but sig
nificantly less spray on leaves than the other treatments but there were no
significant differences in the other. The very fine spray quality treatmen
t deposited significantly less on fruitlets in both experiments, but differ
ences were small. The leaf-to-leaf and tree zone-to-tree zone distributions
of deposits were not affected significantly by the spray quality. The perc
entage spray cover, estimated by image analyses, on water-sensitive papers
fixed horizontally in the middle of the trees was not markedly affected by
spray quality though values were variable. The very fine and fine spray qua
lities gave significantly greater grand mean percentages of spray drift tha
n the medium spray quality treatment in one experiment, though differences
were either not or only just statistically significant in the other. Drift
was greatest in the small trees and least in the large trees, consistent wi
th an inverse relationship with tree area density (TAD). The medium spray q
uality gave significantly smaller deposits on the ground sampling lines tha
n the very fine and fine treatments. In conclusion, variation in spray qual
ity over the range investigated did not greatly affect the amount or macro-
distribution of spray deposits on apple trees from the axial fan sprayer. T
he coarser sprays gave slightly greater mean deposits and smaller spray los
ses and are preferable from these points of view. Further work is required
to establish the effects of spray quality on the micro-distribution of depo
sits on the target. A coarser pattern of spray deposition on the plant surf
ace could be less efficacious biologically for some pesticides. Therefore.
evaluation of the effects of spray quality adjustment on biological efficac
y is required. (C): 2001 Elsevier Science Ltd. All rights reserved.