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Saturday, December 08, 2012
Pomegranate:Cultivation and Farming
Pomegranate
(Punica
granatum)
Cultivation and Farming
Soils and Climate
Soil - Pomegranates are fairly drought tolerant and can be grown
on either calcareous or acid soils. Climate - Grow best in dry climates with
mild winters. Chilling requirement - Unclear; can be grown in tropical climates
without chilling. Cold hardiness - Wood tolerates temperatures down to -11°C.
The pomegranate
thrives on calcareous, alkaline soil and on deep, acidic loam and a wide range
of soils in between these extremes
Propagation
Pomegranate seeds
germinate readily even when merely thrown onto the surface of loose soil and
the seedlings spring up with vigor. However, to avoid seedling variation,
selected cultivars are usually reproduced by means of hardwood cuttings 25-50
cm long. Treatment. indole-butyric acid and planting at a moisture level of
15.95% greatly enhances root development and survival. The cuttings are set in
beds with 1 or 2 buds above the soil for 1 year, and then transplanted to the
field. Grafting has never been successful but branches may be air-layered and
suckers from a parent plant can be taken up and transplanted.
Pollination
The pomegranate is
both self-pollinated and cross-pollinated by insects. There is very little wind
dispersal of pollen. Self-pollination of bagged flowers has resulted in 45%
fruit set. Cross-pollination has increased yield to 68%. In hermaphrodite
flowers, 6 to 20% of the pollen may be infertile; in male, 14 to 28%. The size
and fertility of the pollen vary with the cultivar and season
Cultivar
Types with relatively
soft seeds are often classed as "seedless". Among the best are 'Bedana'
and 'Kandhari'. 'Bedana' is medium to large, with brownish or whitish
rind, pulp pinkish-white, sweet, seeds soft. 'Kandhari' is large, deep-red, with
deep-pink or blood-red, subacid pulp and hard seeds. Others include:
'Alandi'
('Vadki')–medium-sized, with fleshy red or pink, subacid pulp, very hard seeds.
'Dholka'–large,
yellow-red, with patches of dark-pink and purple at base, or all-over greenish-white;
thick rind, fleshy, purplish-white or white, sweet, pulp; hard seeds. The plant
is evergreen, non-suckering, desirable for commercial purposes
'Kabul'–large,
with dark-red and pale-yellow rind; fleshy, dark-red, sweet, slightly bitter
pulp.
'Muscat Red'–small to
medium, with thin or fairly thick rind, fleshy, juicy, medium-sweet pulp, soft
or medium-hard seeds. The plant is a moderately prolific bearer.
'Paper Shell'–round,
medium to large, pale-yellow blushed with pink; with very thin rind, fleshy,
reddish or pink, sweet, very juicy pulp and soft seeds. Bears heavily.
'Poona'–large,
with dark-red, gray or grayish-green rind, sometimes spotted, and orange-red or
pink-and-red pulp.
'Spanish Ruby'–round,
small to medium or large; bright-red, with thin rind, fleshy, rose-colored,
sweet, aromatic pulp, and small to medium, fairly soft seeds. Considered medium
in quality.
'Vellodu'–medium
to large, with medium-thick rind, fleshy, juicy pulp and medium-hard seeds.
'Muscat White'–large, creamy-white
tinged with pink; thin rind; fleshy, cream-colored, sweet pulp; seeds
medium-hard. Bears well. Desirable for commercial planting in South Africa
Culture
Rooted cuttings or
seedlings are set out in pre-fertilized pits (60 cm) deep and wide and are
spaced 3.5-5.5 m apart, depending on the fertility of the soil. Initially, the
plants are cut back to 60-75 cm in height and after they branch out the lower
branches are pruned to provide a clear main stem. Inasmuch as fruits are borne
only at the tips of new growth, it is recommended that, for the first 3 years,
the branches be judiciously shortened annually to encourage the maximum number
of new shoots on all sides, prevent straggly development, and achieve a strong,
well-framed plant. After the 3rd year, only suckers and dead branches are
removed. For good fruit production, the plant must be irrigated.
Pests and Diseases
Pomegranate butterfly,
Virachola isocrates, lays eggs on flower-buds and the calyx of developing
fruits; in a few days the caterpillars enter the fruit by way of the calyx.
These fruit borers may cause loss of an entire crop unless the flowers are
sprayed 2 times 30 days apart. A stem borer sometimes makes holes right through
the branches. Twig dieback may be caused by either Pleuroplaconema or
Ceuthospora Phyllosticta. Discoloration of fruits and seeds results from
infestation by Aspergillus castaneus. The fruits may be sometimes disfigured by
Sphaceloma punicae.
Dry rot from Phomopsis
sp. or Zythia versoniana may destroy as much as 80% of the crop unless these
organisms are controlled by appropriate spraying measures. Excessive rain
during the ripening season may induce soft rot.
Minor problems are
leaf and fruit spot caused by Cercospora, Gloeosporium and Pestalotia sp.; also
foliar damage by whitefly, thrips, mealybugs and scale insects; and defoliation
by Euproctis spp. and Archyophora dentula. Termites may infest the trunk.
Training Young Trees
Trees may be trained
to a bush, single- or multiple-trunked tree. The bush form is satisfactory for
backyards or hedgerows, but is undesirable for good commercial production.
Trees form the nursery
are planted bare root in winter or early spring. The natural growth habit of
the pomegranate is to produce many suckers from the base of the tree. If a
single truck tree is desired, only one vigorous sucker or the trunk of the
original nursery tree should be selected and branches grown from it. Basal
suckers should be removed periodically to promote growth form the main trunk of
the newly planted tree. If the orchard trees are to be developed into a
multiple-trunk system, five or six vigorous suckers should be selected around
the base of the young tree and allowed to grow.
Selection of the five
or six suckers to be developed into permanent trunks may take two or three or
more years until good trunks are correctly positioned to form a sturdy and
symmetrical tree. All other suckers should be removed in summer and during
dormant pruning.
Many growers prefer
the multi-trunk system. In case of frost injury, usually only one or two trunks
are injured, leaving the others to continue bearing. New trunks can be trained
from suckers and full production restored to the tree in 2 or 3 years.
Single-trunked trees may be completely killed except for suckers coming form
the ground. Trees trained to a multiple truck require less frequent care in
pruning during the first few years and come into bearing sooner than trees
having only one truck.
Some pruning and tying
with ropes for support may be needed for the first 3 or 4 years or until trunks
are large and rigid enough to support the developing top.
Pruning
Pomegranate trees
require a small amount of pruning each winter to maintain shape and good
bearing surface. Even mature trees grow vigorously, sending up a large number
of shoots and basal suckers that require removal each year.
The short spurs on 2-
or 3-year-old wood growing mostly on the outer edge of the tree produce
flowers. These spurs develop on slow growing, mature wood that bears fruit for
several years, but as the tree increases in size the wood loses its fruiting
habit. Light, annual pruning encourages growth of new fruit spurs and heavy
pruning reduces yields. Care should therefore be taken to leave adequate
fruit-bearing wood on the tree, while removing crossing over or interfering
branches. In addition, some thinning out of crowded bearing areas helps produce
larger fruit having fewer wind scars.
Should below-freezing
temperatures occur in early winter before trees are fully dormant, or in early
spring when trees are beginning to leaf out, severe damage can be done to tree
trunks. Occasionally, entire trunks are girdled and killed by frost. Remove
weak or dead limbs during the next growing season, and permit a vigorous sucker
to develop from ground level to replace it.
Fertilization
Mature pomegranate
trees require from 1-2kg of actual nitrogen per tree per year. This may be
applied in one application in fall or winter. On light soils a split
application may be desirable, one-half of the fertilizer being applied in late
winter and the remainder in spring. Excessive or late applications of nitrogen
may delay fruit maturity and color. Some evidence indicates that excessive
nitrogen applications cause increased vegetative growth and reduce fruit
production.
There is not evidence
to show that phosphorous (P) or potassium (K) will improve growth or fruit
quality when used to fertilize pomegranate orchards. Occasionally, zinc
deficiency is evident in trees. This is corrected by applying zinc sprays
during the dormant season or to the foliage in spring and early summer.
Irrigation
The pomegranate can
withstand long periods of drought. Although not much fruit is produced under
drought conditions, trees will survive for years; then, if properly irrigated,
they grow vigorously and produce good crops.
Trees will thrive and
produce an abundance of fruit under high summer rainfall conditions but the
fruit tends to be soft and has poor shipping and storage quality.
To produce large crops
of good-quality fruit, pomegranates require about the same amount of water and
frequency of application as citrus. Adequate soil moisture must be maintained
throughout the growing season, particularly as harvest approaches in late
summer and early fall, when it helps reduce the number of split fruit.
Most orchards are
irrigated under the furrow system, but sprinkler and drip irrigation systems
are satisfactory if properly designed. Orchards thrive under noncultivation and
semi-noncultivation systems. Weed control is difficult because at present no
pre-emergence herbicides are registered for use in pomegranate orchards.
Harvesting and Yield
The fruits ripen 6 to
7 months after flowering. The fruit cannot be ripened off the tree even with
ethylene treatment. Growers generally consider the fruit ready for harvest if
it makes a metallic sound when tapped. The fruit must be picked before over
maturity when it tends to crack open if rained upon or under certain conditions
of atmospheric humidity, dehydration by winds, or insufficient irrigation. Of
course, one might assume that ultimate splitting is the natural means of seed
release and dispersal.
The fruits should not
be pulled off but clipped close to the base so as to leave no stem to cause
damage in handling and shipping. Appearance is important, too much sun exposure
causes sunscald–brown, russeted blemishes and roughening of the rind.
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