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Reproduced with permission
of the NZTCA
by Dana Pillai
Pistachio nuts are a crop of great antiquity, thought to have
originated in Central Asia. Up until the war in 1979, Iran was a major
producer of this nut crop The war caused the world's main pistachio supply
to disappear, and caused prices to rise sharply. Pistachio nuts are now
a well-established crop in California, especially in the San Joaquin Valley.
Australia also has a developing pistachio industry.
Pistachio trees are reported to be tolerant of drought, frost
and heat, and to grow at altitudes of up to 1200 m. Of the 11 species in
the genus Pistacia, only P. vera is commercially cultivated for nuts. The
trees are slow growing, small, dioecious bushes that on maturity may reach
8 metres tall and 10m across. The leaves are odd-pinnate with 3 to 11 ovate
leaflets. Male and female flowers are borne on separate trees. The flowers
are borne without petals, in axillary racemes or panicles. A single
fruit develops from each flower as a dry, ovoid to oblong, pedicelled drupe,
up to 2·5 cm long, that is reddish and wrinkled, enclosing 2 yellow-green
oily cotyledons. In Australia flowering occurs in October.
Pistachio trees will grow and survive in a wide range of conditions,
but they have certain requirements for the production of high-grade nuts.
Pistachios require cold winters (less than 5ºC in July, and down to
-18ºC) and long, hot dry summers (more than 32ºC in January,
and up to 38ºC). Also, it is recommended that four out of five Octobers
are frost-free, as spring frost may kill flowers and new vegetative growth.
Pistachios are reputed to thrive where olives and almond trees grow, but
they flower later in the spring than almonds, and are less susceptible
to fruit injury. Pistachios require at least 300-450 mm of annual rainfall,
and irrigation is necessary where the annual rainfall falls below this
threshold. Pistachios will not tolerate high humidity in the growing season.
Approximately 600-1500 hours below 7ºC of winter chilling are necessary,
depending on the cultivar.
Pistachios will not tolerate prolonged wet conditions. Ideally, soils
should be deep, friable and well-drained, but moisture-retaining. Pistachios
are capable of surviving in poor, stony, calcareous, highly alkaline or
slightly acid, or even saline soils, and are more tolerant of these conditions
than most other commercial trees. This makes them valuable trees for reclamation
and conservation projects. Although they are tolerant of a range of soil
pH, a pH between 7.1—7.8 is considered ideal.
Seeds may be planted soon after harvest. Scarification of seed shells speeds
and increases germination. One method of propagation is to spread seeds
in a damp "wettex" roll and keep at 20ºC. Germination begins in about
10 days. As seeds sprout they can be transferred to small pots and later
transferred to milk cartons/PB8s or, if you intend to container-graft,
Scion cultivars are budded onto seedling rootstocks. Because bare-rooted
trees are difficult to transplant it is necessary to establish orchards
with plants grown in containers, or with young rootstocks which are subsequently
P. vera is susceptible to nematodes so other Pistacia species
are used as rootstock. P. atlantica and P. terebinthus have good resistance
to nematodes and soilborne diseases and are used by Australian propagators.
However, both species are susceptible to Verticillium wilt, and in Cali-
ornia P. intergerrima is now used where his disease is a problem. The rootstocks
have varying degrees of cold-tolerance. P. terebinthus is most cold-tolerant,
P. antlantica is susceptible to cold below -7ºC and P. intergerrima
is even less cold-tolerant. When seedling rootstock trees are 2-3m tall,
selected cultivars are bud-grafted to them.
Shield budding or T-budding in the field are the most commonly used techniques.
Buds are large, so the diameter of rootstock should be at least 7-IOmm.
Buds are inserted any time during the period when the bark of the rootstock
slips. Buds may be forced into growth by ringing just above them, or by
cutting back the tops to 0.5m above the buds 2-3 weeks after insertion.
As female flowers are receptive for only about 4 days, male trees
shedding pollen during the first half of female blooming period should
be selected. Usually one male tree is planted to 8 female trees as a 3
x3 block of females with a single male in the centre. Pollination occurs
by wind or air drift, although bees may actually take quantities of pollen
and thereby reduce fruit-set.
Weed control is necessary to reduce water competition and disease.
After grafting, 4-6 years are required before the trees
begin to bear, but they do not bear fully until the trees are 20-25 years
old. Trees may continue to bear for 40 to 60 years or more. The ideal spacing
of mature trees is about 8-10 m. Tree growth is very slow and many orchards
contain temporary filler trees as crowding is not expected for 12-15 years.
The recommended fertiliser application at planting is 50 gms/plant
of 20:10:10 NPK. This rate can be gradually increased yearly to a level
of 40 kg/ha in year 10. Zinc and boron deficiency are commonly encountered,
and foliar analyses may help to identify this before the symptoms become
apparent in the leaves.
Training and pruning
The scion shoot is trained vertically and tied to a stake. A strong
trunk, 12 m high should be developed for mechanical harvesting, and branching
can be stimulated at this point by pinching back the trunk in summer or
at the first dormant pruning. The first 4-5 years are critical to establish
the desired tree shape. The tree is pruned to develop a modified leader
system having 3 well-spaced low scaffold branches. The centre of the tree
should be open.
In humid conditions copper sprays are necessary to clear up leaf
speckling. Verticillium may also be a problem.
In Australia the crop is harvested in March. Nuts are either knocked
down by hand or shaken from the tree by a machine similar to a prune-harvester.
Clusters of nuts removed are allowed to dry 3 days on the ground and beaten
or stamped on to separate the nuts from the clusters. They are next put
in a tank of water to soak for 12 hours and then stamped or beaten to remove
the outer green husk, then washed and dried in the sun. Fresh nuts need
to be held in cold-storage to avoid staining. The sooner the hull is removed,
the less chance there is of shell deterioration or discolouration.
Yields and economics
Trees usually begin bearing in the 4th- 5th year after budding,
but an economic crop is a further 4 years away. In California 8-15 year-old
trees yield 2-8 kg of in-shell nuts/tree, giving 200-800 kg/ha. 16- 30
year old trees yield 8-30 kg/tree (800-2400 kg/ha). Adult trees average
11.25 kg annually, with the Californian state average yield being approximately
1 t/ha. However, pistachios are prone to alternate bearing, with a heavy
crop one year followed by little or no crop the following year. Three kilos
of unshelled nuts are equivalent to one kilo of shelled nuts, with most
nuts marketed unshelled and salted. Using data from 1991 and assuming an
in-shell price of$400 to the grower, 100 ha of trees are required for an
economically viable orchard. At a higher price of $590/kg a 10 ha orchard
could be vi- able. At higher yields this area could be even smaller.
future industry in New Zealand
The pistachio's reputation for climatic extremes has encouraged
tree croppers in Central Otago to try establishing this exotic crop. The
long, hot, dry summers and very cold winters of the inland basins of Otago
more than anywhere else in New Zealand most resemble the climate of the
pistachio homeland. In addition, the generally well-drained alluvial and
sometimes alkaline soils of the region would seem an ideal substrate for
pistachio trees. Care is required to select sites with favourable microclimates
reducing the risk of spring frosts. The cold resistant Pistacia terebinthus
would appear to the most appropriate rootstock. There is little or no data
at this stage to suggest which cultivars would be suitable, and it is highly
likely that the cultivars selected for Californian and Australian conditions
would not be applicable to New Zealand.
Crane, J. C. & Maranto, J. 1982: Pistachio Production; Cooperative
Extension Univ. of California, Division of Agricultural Sciences. Leaflet
2279. 15 pp.
Maggs, D. H., 1982: An Introduction to Pistachio growing in Australia:
CSIRO, Australia. 36 pp.
California Pistachio Commission: California Pistachio Annual
Report Crop Year 1992-1992.172 pp.
Reproduced by permission
of the New
Zealand Tree Crops Association from 'The Tree Cropper', the Official
Journal of the New Zealand Tree Crops Association, Issue number 5, September
Note: this work is '©
Copyright Dhana Pillai and The NZ Tree Crops Association
Inc', regardless that it is permitted to freely distribute it.
Beede, B. et al., 1991: Sample Costs to Establish and Produce
Pistachios in the Southern San Joaquin Valley. Manuscript.