Agriculture Reference
In-Depth Information
girdling is done at the end of the initial small fruit drop. Girdling has been used
to improve avocado fruit size, especially 'Hass' (McNeil, 2001). A longer-term
objective is the elimination or modifi cation of biennial bearing in some tropical
and subtropical fruit trees. Litchi girdling is done before fl ush initiation,
around September in the northern hemisphere, to induce more fl owering
and increase fruit yield. Only one of the three or four main branches should
be girdled, in order to avoid the danger of killing the tree. Girdling should be
preceded by a heavy irrigation and fertilization for better results. Normally if
there was a poor crop the previous year, girdling will work, while if there was
a heavy crop, no girdling should be done. It is recommended that girdling or
scoring be done for no more than 3 years in a row. Girdling is not a standard
practice and, in many cases, growers will use it when they have marginal
yields and will forget about this practice when good yields are being obtained.
DEFOLIATION
Most tropical fruit trees are evergreen and usually do not shed their leaves.
An exception is some
Spondias
species that lose their leaves during the dry
season as a drought-protection mechanism. The trees begin fl owering while
completely bare. Some other trees, such as avocados in the subtropics, might
have a heavy loss of leaves just before fl owering time. Artifi cial defoliation is
practised in dii cult-to-graft trees, where the portion of the branch from which
bud-wood is going to be taken is defoliated 2 or 3 weeks prior to collecting the
scions. This defoliation stimulates the lateral buds to start swelling and become
more active, and ensures better budding or grafting success.
Cherimoya and atemoya, being more subtropical, are sometimes classifi ed
as semi-deciduous. The lateral buds of these species are covered by the leaf
petioles (see Fig. 6.1) and are not at the leaf axils, as in most plants. Thus the
leaves have to fall or be removed for the bud to burst. Defoliation is done to
induce uniform sprouting of these buds just before the new growth is about to
start and natural defoliation has not been complete. This is achieved by hand-
stripping or with the application of urea or other defoliants, at the time of
pruning, to induce a new cycle of fl owering and fruiting.
PLANT GROWTH REGULATORS AND OTHER STIMULANTS
Plant regulators have been studied for many years and some practical uses
have been developed. Among the most common uses of plant regulators is the
improvement of rooting of cuttings or air layers with auxin-like compounds
such as indole butyric acid (IBA) or naphthalene acetic acid (NAA). These
auxins improve rooting percentage, accelerate adventitious root emergence
and increase the number of roots a layer or cutting will form.
