Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
stripping, or chemical removal, with urea or ethephon, will release these buds
(George and Nissen, 1987). However, this technique is not recommended for
soursop. Bonaventure (1999) describes this method as 'green pruning' and
affirms that it is very important in cherimoya. He mentions the two most
important types of green pruning: the first type to reduce excessive
vegetation; and the second to separate the two or three new leaves, followed
by removal of the apical bud with the finger nail. According to this author, it
is possible to promote late production by using green pruning.
George et al. (1987) commented that chemical pruning by defoliation of
cherimoya and sugar apple trees is necessary for cultivars exhibiting strong
apical dominance, since light fruiting-pruning may not be sufficient to
release many buds from induced dormancy. They also commented that a
range of defoliants have been investigated, but a mixture of 250 g urea and
1 g ethephon, plus wetting agent, in 100 litres of water has been most
successful. Two defoliation periods are possible: a) at 5 to 10% bud-break,
when the new shoots are about 3 to 5 cm long; and b) at mid season (first
week of January in Australia), applied to non-bearing trees, usually 2 to 3
years of age.
Pruning for production of sugar apple is very important, since bearing sugar
apple trees seem to deteriorate, in terms of fruit production, faster than any
other annona (Coronel, 1994). The heading back of the branches at the onset
of dormancy to rejuvenate sugar apple trees will result in resumed production
after 2 years (Coronel, 1994). Dormancy of sugar apple buds depends on the
climate. In south-eastern Brazil, dormancy is due to low temperatures
between May and July, while in the semi-arid areas of the north-eastern
region it is due to strong drought (water stress) during several months (Kavati
and Piza Jr., 1997).
In Thailand, sugar apple trees are rejuvenated every year to produce new
fruiting shoots. This operation consists of removing all small shoots and
heading back larger shoots to about 10-15 cm long (Coronel, 1994). This
operation is carried out during the dry season, just prior to shedding of the
leaves; the plants are then irrigated to promote new shoots and irrigation is
continued until the rainy season starts. This is the same procedure as in northeastern
Brazil.
The pruning for production of sugar apple should begin with 1-year-old
branches by cutting them back to 10 cm and leaving 120-150 branches per
tree (Nakasone and Paull, 1998); flower initiation will then begin at the basal
end of the new growing branch. In China and Taiwan, normal fruit pruning
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