Almond

Prunus dulcis

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Description

The almond tree, Prunus dulcis, is a deciduous tree in the family Rosaceae which is grown for its edible seeds (nuts). The tree has brown or gray bark and either an erect or weeping growth habit depending on the variety. The trunk can reach 30 cm (12 in) in diameter. Almond leaves are 7.5–13 cm (3–5 in) long with a serrated edge and grow alternately on the branches. The tree produces white to pale pink flowers and hairy green fruits which are oblong in shape. The fruit is a drupe, containing a single seed. The seed is protected by a hard brown shell. At maturity, the flesh of the fruit becomes leathery and splits to reveal the nut inside. Nuts generally measure 3.5 to 6 cm (1.4–2.4 in) in length. Almond trees can reach heights between 4 and 10 m (13–33 ft) and have a commercial lifespan of between 30 and 40 years. Almond may be referred to by variety and this includes bitter almond almond nuts are generally about long and may also be referred to as sweet or bitter almond depending on variety and originates from wild species found in Central and Southwest Asia.

Uses

The almond nut is eaten raw or processed into butter, flour, extract, oil, paste, syrup, and milk. Almond oil is used as a flavoring agent in baked goods, perfumery and medicines. Sweet almond oil is used for cosmetic creams and lotions.

Propagation


Basic requirements
Almond grows best in Mediterranean climates with warm, dry summers and mild, wet winters. The optimal temperature for their growth is between 15 and 30°C (60–85°F) and the tree buds have a chilling requirement of between 300 and 600 hours below 7.2°C (45°F) to break dormancy. Almond trees will grow best when planted in deep, well-draining loam although they can withstand drought and grow in poor soils. The trees benefit from being planted in areas sheltered from frost and wind as trees bloom early and can therefore be susceptible to damage from late frosts. Trees will generally bear nuts after 3 to 4 years with the nut crop developing after blossom, in the fall.

Propagation
Almond trees are most commonly propagated by budding. Dormant wood is collected in winter when the trees are dormant and stored until Spring. T-budding is usually carried out in Spring and involves joining a bud from one variety to the rootstock of another. The bud is taken from a parent with desirable characteristics and grows to produce a new tree. Trees may also be propagated by grafting. Cuttings are taken from trees during dormancy and grafted to a suitable rootstock in the Spring.

Planting
Once trees have been acquired from a nursery, it is important to plant as soon as possible and keep the roots moist in the meantime. Almond trees should be planted by digging a hole just deep enough to accommodate the root ball. The tree should be planted by carefully backfilling the soil into the hole around the tree after it has been properly positioned. Planting depth should not exceed the height of the graft union. The soil around the newly planted tree should then be tamped and watered deeply but not excessively. If planting multiple trees then they should be spaced in rows 6–7 m (20–23 ft) apart with 5–6 m (16–23 ft) between each tree.

Pruning
Almond trees should be pruned in the first year and every subsequent year to help thin the canopy and prevent disease. The first pruning is critical in establishing the canopy shape. Three limbs should be selected to form the basis of the trees canopy and all others removed, including any growth below the lowest limb. In the second year, two scaffolds (lateral branches which grow to form a Y with the primary limbs) should be selected and the rest removed. Aim for the remaining scaffolds to be evenly spaced around the canopy.

General care and maintenance
Almond trees will benefit from a layer of mulch around the base to prevent the growth of weeds and conserve soil moisture. Mulch should be spread around the tree in a 1 m (3 ft) radius. Leave a gap between the mulch and the trunk to prevent rotting the trunk. In addition, an application of fertilizer should be made once in Spring before any new growth and again in the Fall.

Diseases

Almond brownline and decline Phytoplasma Peach yellow leafroll mycoplasma

Symptoms

Stunted tree growth; drooping/wilting of leaves; brown necrotic areas under bark

Comments

Most common on young trees; grow trees from pathogen free stock

Management

Stunted trees should be removed and replaced; plant only certified pathogen free trees

Almond kernel shrivel Phytoplasma Peach yellow leafroll phytoplasma

Symptoms

Late blooming; new growth stunted; paler, smaller leaves; kernels of nuts shriveled at harvest

Comments

Most common where peach rootstock has been used for grafting; remove infected trees

Management

Remove diseased trees; plant only certified trees

Almond leaf scorch; golden death Bacterium Xylella fastidiosa

Symptoms

Chlorotic leaf margins; necrosis of leaf margins beginning toward tip of leaf and spreading to base; patches of necrotic tissue with chlorotic margin

Comments

More of tree will be affected each year; bacterium can infect rye, blackberry and nettle and if these plants are nearby they may act as reservoir; transmitted by leafhoppers and spittle bugs

Management

If discovered early (while disease affects only one branch) disease can be removed by pruning primary scaffold 5 to 10 ft below symptoms; older infections may require the tree to be removed and replaced

Alternaria leaf spot Fungus Alternaria alternata

Symptoms

Light brown lesions on leaves which expand to form circular lesions on leaf blade or semi-circular lesions on margin; leaves may develop light yellow necrosis which dries and turns tan in center of leaves; infected leaves dropping from tree; fruit does not drop from tree

Comments

Disease emergence favors warm weather

Management

Late spring treatment with appropriate fungicide if Alternaria symptoms are present

Anthracnose Fungus Colletotrichum acutatum

Symptoms

Blighting of blossom; dieback of limbs; death of foliage with leaves remaining attached; nuts with orange lesions

Comments

All cultivars susceptible; occurs more often in warm, wet conditions

Management

Fungicide treatment and cultural practices required to control disease. Orchards with a history of anthracnose infections should be sprayed at 5-10% bloom and applications should be repeated every 10 to 14 days; dead infected branches should be pruned; low angle nozzles should be used in orchards with spray irrigation to prevent wetting of leaves

Brown Rot Blossom Blight Fungus Monolinia laxa

Symptoms

Blighted blossoms; stigma and anther of flowers turning brown and necrotic; blossom collapsing and turning brown; light brown powdery fungal masses may be visible on infected flowers; gummy exudate at base of flowers; cankers forming on twigs associated with blossoms

Comments

Disease emergence favors frequent rainfall during bloom

Management

Fungicide application at 5-10% bloom and full bloom to protect flowers; one application at full bloom usually sufficient if there is no rainfall; two or three applications should be made if bloom is accompanied by rainfall

Crown gall Bacterium 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

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

Hull rot Fungus Rhizopus stolonifer
Monolinia spp

Symptoms

Tan lesions on hulls which enlarge and cause fruit to shrivel; dark gray spore masses visible between hull and shell; leaves in proximity to infected fruit may wither and curl; leaf death occurs on side of shoot closest to infected fruit

Comments

Hulls of fruit are susceptible to hull rot until they are dry

Management

Management of irrigation should be practiced. Reduce irrigation at hull split; demethylation inhibitor and quinone outside inhibitor fungicide may be applied in combination with irrigation management

Pavement ant (Southern fire ant) Insects Tetramorium caespitum
Solenopsis xyloni, S. molesta

Symptoms

Hollowed out nuts on ground

Comments

Prevalent in orchards using drip or spray irrigation

Management

Monitor orchard for ants in April and May; apply ant baits before harvest to manage high ant populations; remove nuts from orchard floor as soon as possible

Shot hole Fungus Wilsonomyces carpophilus

Symptoms

Circular purplish spots on foliage which enlarge and turn chlorotic then tan; drying of lesions causes missle of lesion to drop out of leaf causing small holes to develop

Comments

Spores transmitted in water; disease more common in wet conditions

Management

If fungal fruiting structures are present in Fall (visible under a hand lens as small black spots in the center of lesions) then a fall treatment with fungicide is required; fungicide should be applied before wet periods to protect tree

Verticillium wilt (Blackheart) Fungus Verticillium dahliae

Symptoms

Leaves on one side of tree turning yellow; wilting early in season

Comments

Fungus overwinters on soil, recurring each year; problematic if orchard is interplanted with other susceptible plants e.g. cotton, tomato, melon

Management

Orchards should not be intercropped with susceptible plants e.g. cotton, tomatoes or melons; solarization or fumigation of soil prior to planting may be used to kill fungi in soil

References

CABI Crop Protection Compendium. (2010). Prunus dulcis datasheet. Available at: http://www.cabi.org/cpc/datasheet/44279. [Accessed 05 November 14]. Paid subscription required

Doll, D., DeBuse, C. & Beede, B. (2011). Almond Pruning and Training. UC Davis Fruit and Nut Research and Information. Available at: http://fruitsandnuts.ucdavis.edu/almo.... [Accessed 05 November 14]. 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

Webb, D.A. (1998). Prunus dulcis (Mill.).Purdue University Center for New Crops and Plant Products. Available at: http://www.hort.purdue.edu/newcrop/du.... [Accessed 05 November 14]. Free to access