Agriculture Reference
In-Depth Information
If the trees when planted do not have enough lateral branches, ideally more
than ten, additional branches can be induced in the orchard by:
Heading-back, i.e. removing the apical part of the tree to stimulate bud-
break below the pruning cut.
Notching, i.e. removal of a thin band of bark above each lateral bud.
Periodic removal of immature apical leaves.
Tying the leading shoot down, first in one direction then in the other.
Spraying with Promalin (BA
+
GA
+
).
Each of these can be effective but their individual utility varies with the initial
level of branching, with cultivar and with growing conditions (Volz
et al.
,
;
Parker and Young,
).
These techniques can also induce budbreak on older trees, but reducing
apical dominance by training branches to a horizontal or a nearly horizontal
orientation assumes greater importance. In many systems of tree management
the angle made by the lateral branches to the main stem is increased by
tying them down to pegs in the ground, weighting them with transferable
concrete weights, inserting 'spreaders' between the main stem and the branch,
or training the branches along wires.
Under subtropical conditions with limited winter chilling, branching in
the nursery and orchard can be induced by cold storage of nursery trees or
chemical treatments (pp.
; Ouellette
et al.
,
-
).
Seasonal bud dormancy
Introduction
Seasonal plant dormancy is, in general, a mechanism for surviving regularly
recurring periods (seasons) of drought or low temperature.
Seasonal dormancy in apples and pears can be expected to be adapted
to conditions at their centres of origin and also to conditions in the areas in
which the cultivated varieties have been selected. In some of these climates
temperatures become so low in winter that shoots, stems and roots which have
not 'hardened' are killed, and cessation of growth is a precondition for such
hardening (Westwood,
). The capacity to initiate physiological changes
in advance of potentially lethal conditions, and for buds (and seeds) to re-
main dormant in winter until there is little risk of lethal frost, must have been
essential features of adaptation in the wild. The adverse economic effects of
even intermittent frost damage to buds and blossom have also resulted in se-
lection pressure for appropriate timing of budbreak of cultivated apples and
pears.
