Agriculture Reference
In-Depth Information
Defoliation is used to modify or manipulate bud dormancy, both in tropical
conditions without strong seasonal patterns of temperature and in the sub-
tropics where chilling is inadequate. In Indonesia, leaf stripping one month
after harvest results in budbreak, mainly of terminal buds on long shoots and
spurs, within
days. If the stripping is carried out too soon after harvest
the buds have not yet developed to give flower buds, so the growth is purely
vegetative. Carried out at the right time, the buds are mixed buds, i.e. produce
flowers as well as leaves. Two crops a year can be obtained in this way ( Janick,
to
). This tech-
nique is effective with cultivars normally considered to have a high chilling
requirement, e.g. 'Rome Beauty', and is essentially based on prevention of
entry into endodormancy.
InMexicodefoliationiscarriedoutincircumstanceswherenormalleafdrop
does not occur. Chemical defoliation induces more budbreak than manual
defoliation and is particularly effective if carried out in early January after
some chilling has occurred. Diaz
et al.
(
; Edwards and Notodimedjo,
; Notodimedjo
et al.
,
) reported very positive effects of
defoliation by use of copper sulphate or urea applied to 'Anna' apple trees.
Bending branches towards the horizontal is widely practised in the tropics.
This may have a direct effect on the depth of bud dormancy, as shown by
Crabb´e(
b). It also has the very important effect of releasing lateral buds
from apical dominance. These grow out to give numerous short shoots or spurs
along the upper surface of the branches. Such spurs bear terminal buds which
break dormancy with less chilling than lateral buds on intact shoots, and these
spurs give most of the crop in the Indonesian production system ( Janick,
;
Erez and Lavi,
).
Induction of water stress by stopping irrigation in a dry environment is
commonly used in warm-winter conditions together with the above tree man-
agement practices to provide an effective substitute for winter chilling.
Mineral oils in conjunction with chemicals such as dinitro-ortho-cresol
(DNOC) were widely used from the late
s as dormancy-breaking agents
in countries such as South Africa with sub-optimal winter chilling. Their use
has been largely discontinued because of toxicity to humans (Erez,
).
Hydrogen cyanamide is very effective as a bud-breaking agent for a wide
range of apple cultivars ( Jackson and Bepete,
) and for pears including
P. pyrifolia
(Krisanapook and Subhadrabandhu,
). It can be used in the
early orchard years to stimulate vegetative budbreak and lateral branch pro-
duction. When used in cropping orchards it induces budbreak, compresses
the period of budbreak within a cultivar and synchronizes the flowering, i.e.
breaking of mixed buds, of different cultivars. As with a number of other
