Growing Pistachio Nuts in Otago, New Zealand

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Reproduced with permission of the NZTCA by Dana Pillai Introduction 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.

Climatic requirements 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. Soil preference 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. Seed germination 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, to PB12s. Rootstocks 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 field-grafted.
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. Budding 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. Pollination 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. Orchard establishment 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. Diseases In humid conditions copper sprays are necessary to clear up leaf speckling. Verticillium may also be a problem. Harvesting 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. A 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.

References
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.

Beede, B. et al., 1991: Sample Costs to Establish and Produce Pistachios in the Southern San Joaquin Valley. Manuscript.

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 1995. Note: this work is '© Copyright Dhana Pillai and The NZ Tree Crops Association Inc', regardless that it is permitted to freely distribute it.