Pistachio

Description

Pistachio, Pistacia vera, is a deciduous tree in the family Anacardiaceae grown for its edible seeds (nuts). Pistachio is a small to medium sized tree with a branching main stem (trunk) and a spreading growth habit. The leaves of the pistachio are pinnate and composed of five individual oval leaflets. Male and female inflorescences are produced on different trees (dioeceous).The flowers are small, brownish-green in color and lack petals. They are produced on panicles, each possessing several hundred flowers. The fruit of the tree is a drupe with an oblong kernel covered with a thin, bony shell. The shell splits along its long axes when mature. Pistachio trees can reach up to 20 ft (65.6 ft) in the wild but are generally smaller under cultivation. They reach maximum productivity in terms of fruit production after approximately 20 years and can live for several hundred years. Pistachio may also be referred to as green almond and originated from western Asia.


Uses

Pistachio nuts are eaten as a snack food, usually after salting and roasting.


Propagation


Basic requirements
Pistachio trees grow best in areas with a long hot summer and cold winter as the tree has a chilling requirement. The tree is tolerant of frost and can withstand winter temperatures as low as -20°C (-4°F). Trees are also drought resistant and can be grown on a wide range of soils, including rocky or stony soils, without irrigation but trees will grow optimally in well draining, deep sandy loams. Pistachio trees are wind pollinated and require the planting of both male and female trees for successful pollination and fruit set.

Propagation
Pistachio is usually propagated by budding on to a suitable pistachio rootstock. Rootstock varieties vary widely between growing areas. Budding is usually carried out in the Fall with the budded tree being planted the same year or the following year depending on the size of the seedling. Young trees are planted by digging a hole large enough to accommodate the root ball. The tree should be planted about an inch lower than it was grown in the container. Tree spacing varies depending on whether irrigation is used. In irrigated orchard, trees can be spaced in a 6 × 6 m (19.7 × 19.7 ft) grid pattern. In arid regions where supplemental irrigation is not used, trees may be spaced 8 × 10 m (26.2 × 32.8 ft) apart. Both male and female trees must be planted in order for the trees to bear fruit. Ratios of males to females vary from 1:8 to 1:11 males to females.

General care and maintenance
Pistachios have a similar nitrogen requirement to other nut trees. Fertilizer should not be applied in the first year following planting but in the subsequent year, each tree should be supplied with 1 lb of ammonium sulfate split between two applications over the course of the growing season. In the years following, trees should be fertilized with actual nitrogen with application rates varying from 100 to 150 lb per acre. The nitrogen should be split evenly into two applications over the growing season. no nitrogen should be applied after June to prevent vigorous growth that may delay the tree entering dormancy, potentially leading to damage from early frosts.

Harvesting
Newly budded pistachio trees will not begin to produce fruit for five years and will not reach maximum production until the twelfth year. Nuts are ready to harvest when the hull separates easily from the shell. This period extends for 7 to 10 days. If nuts are harvested before or after this critical period kernels may be underdeveloped and shells may become stained.



References

CABI Crop Protection Compendium. (2008). Pistacia vera (pistachio) datasheet. Available at: http://www.cabi.org/cpc/datasheet/41033. [Accessed 30 March 15]. Paid subscription required.

Herrera, E. (1997). growing pistachios in New Mexico. New Mexico State University Cooperative Extension Service. Available at: http://aces.nmsu.edu/pubs/_circulars/.... [Accessed 30 March 15]. Free to access.

Teviotdale, B. L., Michailides, T. J. & Pscheidt, J. W. (eds) (2002). Compendium of Nut Crop Diseases in Temperate Zones. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.


Common Pests and Diseases

Pistachio dieback
Xanthomonas translucens

Symptoms
Dieback of twigs and branches; tree producing an excessive amount of resin; black, sooty lesions present on trunk and branches; dark staining of vascular tissues; the disease does not cause any lesions on leaves or fruit
Cause
Bacterium
Comments
Serious disease of pistachio in Australia; pathogen enters plant through wounds; can be spread by contaminated pruning shears
Management
Disinfect tools and equipment thoroughly between use

Crown gall
Agrobacterium tumefaciens

Symptoms
Galls of various sizes on roots and root crown below the soil line; galls may occasionally grow on the trunk; galls are initially light colored bulges which grow larger and darken; galls may be soft and spongy or hard; if galling is severe and girdles the trunk then young trees are weakened due to constricted vascular tissue; trees may be stunted and rarely die
Cause
Bacterium
Comments
The bacterium enters host plants through wounds and causes plant cells to proliferate and cells to be undifferentiated, leading to the formation of a gall
Management
Only plant disease-free nursery stock; plant trees in well-draining soils; avoid wounding the plants as much as possible; fresh wounds can be treated with a biocontrol agent (Agrobacterium tumefaciens K84), if available, to prevent the bacterium colonizing

Alternaria late blight (Alternaria leaf spot)

Symptoms
Black angular to circular lesions of leaves which enlarge and coalesce, forming tan patches; small black lesions on immature nuts; lesions enlarge and coalesce; staining on hull; moldy kernels; severe infestation on leaves can cause premature defoliation
Cause
Fungus
Comments
Disease emergence favors high temperature and high humidity; fungus survives on plant debris
Management
The disease is difficult to control and all pistachio cultivars used commercially are susceptible; applications of appropriate fungicides may help to reduce the incidence of the disease; good irrigation practices should be followed; practices that reduce the wetness of the ground around plants is recommended

Armillaria root rot (Oak root fungus)
Armillaria mellea

Symptoms
Small, discolored leaves which drop early; death of branches; death of plant; clusters of honey-colored mushrooms may sprout at base of plant
Cause
Fungus
Comments
Fungus can survive on dead roots
Management
Armillaria root rot cannot be effectively controlled once it has become established in an orchard; diseased or dead plants should be uprooted and removed; planting resistant rootstocks is the most effective method of preventing the disease

Panicle and shoot blight
Botryosphaeria dothidea

Symptoms
Black circular spots on on leaves, shoots and rachis; black lesions may be present at the base of shoots if bud has been infected; leaves on infected shoots begin to wither and results in blighted shoots which are visually distinct from surrounding green leaves; if lesions occur on petioles the leaflet will die; infection of rachis which move into shoots can result in sunken cankers on the trunk; cankers may exude a dark substance
Cause
Fungus
Comments
Fungus survives in dead infected material that remains on trees
Management
The disease is very difficult to control and treatment relies on a combination of pruning, fungicide application and good irrigation practices; multiple applications of an appropriate fungicide are required over the summer months; infected areas should be pruned by cutting 5 cm below symptomatic areas to reduce inoculum the following year; if sprinkler irrigation is used then water should be directed away from the tree canopy

Powdery mildew
Phyllactinia guttata

Symptoms
Small powdery white patches on leaves and fruit which can expand to cover the entire leaf or fruit surface; small black fungal fruiting bodies are often visible in the white patches
Cause
Fungus
Comments
Disease emergence favored by moderate temperature, poor air circulation around plant and shady conditions
Management
Disease does not cause severe damage to pistachio and control is not warranted

Septoria leaf spot
Septoria spp.

Symptoms
Symptoms vary depending on the species of the fungus; clusters of small dark spots on leaves around secondary leaf veins; clusters enlarge and may cover large areas of the leaves; spots often coalesce to form large dark patches; later, patches turn chlorotic and then necrotic; disease may also present as angular brown spots on leaves which enlarge and coalesce to form large necrotic patches, or as numerous brown spots on both upper and lower leaf surfaces which possess black dots in the center
Cause
Fungus
Comments
Fungi overwinter in fallen leaves from previous season; disease is common in Mediterranean growing regions and in the Middle East
Management
Control of the disease relies on preventative applications of appropriate fungicides which should be started when the first leaves expand and be repeated monthly thereafter

Rust
Uromyces terebinthi

Symptoms
Round or irregularly shaped red-brown pustules on leaves, flowers, pedicels and/or fruit; leaves drop from tree prematurely and fruit become misshapen; leaves redden in late summer
Cause
Fungus
Comments
Disease occurs on pistachio trees in the Mediterranean, India and the Middle East; there have been several severe outbreaks of the disease in the Mediterranean
Management
Disease is controlled by the application of appropriate fungicides

Pistachio psyllid
Agonoscena targionii

Symptoms
Leaves turning yellow and necrotic; curling leaves; leaves drying out; leaves dropping from plant prematurely; leaves may be covered with sticky honeydew and/or sooty mold; adult insect is generally yellow in color with brown spots or rings on the abdomen; adult insect is winged whereas nymphs lack wings
Cause
Insect
Comments
Insect excretes sticky honeydew which encourages growth of sooty mold
Management
Control typically relies on the application of appropriate insecticide but the insect has developed resistance to organophosphates in certain countries such as Syria

Pistachio twig borer
Kermania pistaciella

Symptoms
Young flower clusters turning black and falling from trees; fruit dropping from tree; poor growth of twigs; adult insect is a small, dark colored moth which lays its eggs on flower clusters; larvae bore into the cluster and tunnel towards twigs excreting a dark colored frass (excrement)
Cause
Insect
Comments