Agriculture Reference
In-Depth Information
dormancy-breaking treatments its effect is cumulative over years, stimulation
of vegetative budbreak resulting in the production of both lateral branches
and spurs. This results in the tree having many more buds which, in turn, can
be induced to break.
Hydrogen cyanamide can induce the budbreak of single buds when painted
on these at a concentration of
%, and may be used in this way in the early
years of the trees to economize on material. Lower concentrations, e.g.
.
.
-
).
The dinitro compounds only induced budbreak if applied when there were
already signs of bud growth, but hydrogen cyanamide can be effective on
endodormant buds and is damaging if applied after the buds have started
to grow (Erez,
.
%, showed promise if combined with
-
% winter oil (North,
) found that cyanamide had
a smaller effect if applied to buds early in December than in the months
before and after this when endodormancy could be expected to be less
deep.
Hydrogen cyanamide application synchronizes budbreak both within and
between cultivars. The dates of full bloom of
). Subhadrabandhu (
apple cultivars in Zimbabwe
ranged from
/
to
/
when treated with hydrogen cyanamide, from
/
to
/
if untreated ( Jackson and Bepete,
). This is in conformity
with the results of Subhadrabandhu (
) from which it could be inferred
that cyanamide can induce budbreak largely irrespective of unfilled CU and
GDH requirements. In Zimbabwe, with fewer than
chilling hours below
◦
C, the cropping response to cyanamide was positively correlated with
the chilling requirement of the cultivar as shown by the date of budbreak on
untreated trees, i.e. it overcame the shortfalls in cropping due to inadequate
chilling (Table
.
).
Anumberofotherchemicals,e.g.potassiumnitrate,thioureaandgibberellic
acid, have been found to have some effects on budbreak under subtropical
conditions (Erez,
.
), gibberellic acid being the most effective (El-Banna
et al.
,
).
Shoot extension growth
The total shoot growth on a tree in one year depends on the number of buds
that break, as has already been discussed, and the growth of these individual
shoots. This growth is controlled by a large number of separate, though often
interacting, factors.
Use of reserves in shoot growth
The growth of shoots in spring starts with cambial activity in the stem be-
fore budbreak. Evert (
,
), cited by Oliveira and Priestley (
)
