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.
Almonds in tree
Almonds and blossoms
Almonds
Flower close-up
Almonds in Spring
Almond trees in blossom
Almond blossoms
Almonds on a branch
Almond flower bud
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.
Almond harvesting
References
CABI Crop Protection Compendium. (2010). Prunus dulcis datasheet. [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/almondpages/AlmondPruningTraining/. [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/shopapspress/Pages/42848.aspx.
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/duke_energy/Prunus_dulcis.html. [Accessed 05 November 14].
Free to access
Common Pests and Diseases
Diseases
Category : Other
Almond brownline and decline
Peach yellow leafroll mycoplasma
Symptoms
Stunted tree growth; drooping/wilting of leaves; brown necrotic areas under bark
Cause
Phytoplasma
Comments
Management
Stunted trees should be removed and replaced; plant only certified pathogen free trees
Almond kernel shrivel
Peach yellow leafroll phytoplasma
Symptoms
Late blooming; new growth stunted; paler, smaller leaves; kernels of nuts shriveled at harvest
Cause
Phytoplasma
Comments
Management
Remove diseased trees; plant only certified trees
Category : Bacterial
Almond leaf scorch; golden death
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
Cause
Comments
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
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
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
Category : Fungal
Alternaria leaf spot
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
Cause
Fungus
Comments
Management
Late spring treatment with appropriate fungicide if Alternaria symptoms are present
Anthracnose
Colletotrichum acutatum
Symptoms
Blighting of blossom; dieback of limbs; death of foliage with leaves remaining attached; nuts with orange lesions
Cause
Fungus
Comments
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
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
Cause
Fungus
Comments
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
Hull rot
Rhizopus stolonifer
Monolinia spp
Monilia on a tender fruit Almond
Monilia on a tender fruit Almond
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
Cause
Fungus
Comments
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
Shot hole
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
Cause
Fungus
Comments
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)
Verticillium dahliae
Symptoms
Leaves on one side of tree turning yellow; wilting early in season
Cause
Fungus
Comments
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