Apricot

Description

Apricot, Prunus armeniaca is a deciduous tree in the family Rosaceae grown for its edible fruit. The apricot tree is has an erect growth habit and a spreading canopy. The leaves of the tree are ovate with a rounded base, pointed tip and serrated margin. The tree produces white to pink flowers, singly or in pairs, and a fleshy yellow to orange fruit. The apricot fruit is a drupe with skin that can be smooth or covered in tiny hairs depending on the variety and a single seed enclosed within a protective outer shell (stone). Apricot trees can reach 8–12 m (26–39 ft) and can live anywhere between 20 and 40 years depending on variety and growth conditions. Apricots may have as many as three centers of origin in China, Central Asia and the Near East.


Uses

Apricots can be consumed fresh or dried. They may also be processed into jams and jellies, syrup or juice.


Propagation


Basic requirements
Apricots have a high genetic variability and as a result, they also have a wide range of growing conditions. The trees tend to bloom early compared with other stone fruits and are therefore susceptible to damage from late frosts. Apricots will grow best in deep, well-draining soils and will not tolerate water saturating. Apricots have a chilling requirement (period of cold required to break dormancy) of between 250 and 1200 hours below 7°C (45°F) depending on the variety. In addition, most apricot trees do not require a second variety for cross-pollination.

Propagation
Apricot trees are usually propagated vegetatively to maintain the desirable genetic characteristic of the parent. Trees can be propagated from cuttings or by budding and grafting. Cuttings are lengths of stem usually taken from the previous years growth of an established tree. Cuttings are taken in late winter or early spring and rooted so that they produce a whole new tree. Budding and grafting involves joining two genetically distinct plants one is used for the lower part called the rootstock and another is used for the upper part, known as the scion. The scion is attached by inserting a bud from the desired variety under the bark of the rootstock so that it produces a new tree.

Planting
Apricot trees should be planted in full sun. In colder regions it is beneficial to plant them close to a north facing wall which helps reduce the speed with which the trees warm in the spring, delaying bloom. Plant bare root trees in a pre-dug hole which is slightly wider than the root ball. Backfill the hole so that the tree is planted to its original planting depth. It is usually possible to identify this from changes in the color of the bark. If planting multiple trees, space them at least 7.6 m (25 ft) apart.

General care and maintenance
Apricots should be pruned annually and are generally trained to an open center. Annual pruning encourages new fruit spurs. When the tree is bearing fruit, it is important to thin the fruits to leave 3 or 4 per cluster. This allows fruits to become larger and prevents the tree from reducing production the following year. Trees should be watered regularly during the growing season to aid with fruit development. During dry periods, water trees every 10 to 14 days. Apply water deeply and widely, to at least the width of the canopy. Trees will also benefit from the application of a nitrogen fertilizer in Spring.


References

CABI Crop Protection Compendium. (2013). Prunus armeniaca datasheet. Available at: http://www.cabi.org/cpc/datasheet/44249. [Accessed 05 November 14]. Paid subscription required

Roper, T., Mahr, D. & McManus, P. (1998). Growing Apricots, Cherries and Peaches in Wisconsin. University of Wisconsin-Extension, Cooperative Extension. Available at: http://learningstore.uwex.edu/assets/.... [Accessed 05 November 14]. Free to access

Lamb, R. C. & Stiles, W. C. (1983). Apricots for New York State. New York's Food and Life Sciences Bulletin No. 100. New York State Agricultural Experiment Station. Available at: http://ecommons.library.cornell.edu/b.... [Accessed 05 November 14]. Free to access

Ogawa, J. M., Zehr, E. I., Bird, G. W., Ritchie, D. F., Uriu, K. & Uyemoto, J. K. (Eds) (1995). Compendium of Stone Fruit Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press



Common Pests and Diseases

Bacterial canker
Pseudomonas syringae

Symptoms
Cankers on twigs at bases of flower and leaf buds, in pruning wounds or at the base of spurs which exude amber colored gum; cankers spread upwards and form sunken areas in winter; if pathogen enters dormant buds they may be killed or open normally in Spring before collapsing in early Summer; infected buds may be symptomless.
Cause
Bacterium
Comments
Disease emergence favors high moisture and low temperatures in the spring; young trees particularly susceptible; trees grown in sandy soils that drain poorly are also susceptible.
Management
Ensure that a suitable apricot variety and rootstock is chosen based on geographic location and environmental conditions to prevent stress to tree which predisposes tree to canker disease; apply protective copper spray to trees before flowering; prune trees in early summer to decrease likelihood of infection.

Crown gall
Agrobacterium spp

Symptoms
Galls on root and/or crown of tree which can range in size from so small they are not visible to the naked eye up to 10 cm (4 in) in diameter; galls first become visible as white, fleshy swellings that grow rapidly and become tan to brown in color; galls typically develop at the site of a wound and new galls form adjacent to old ones the next year.
Cause
Bacterium
Comments
Infection with crown gall begins at the site of plant wounds; disease emergence is favored by poorly-drained, alkaline soils and previous feeding damage by nematodes.
Management
Chemical control of the disease is generally ineffective; an effective bacterial biological control is available for commercial production; cultural control methods include: planting only certified, disease-free material, planting apricot in well-draining soil, rotating infected fields with a non-host before apricot is planted and also using good sanitation practices.

Brown rot blossom
Monolinia spp.

Symptoms
Death of young blossoms and associated twigs and leaves; small tan cankers with dark margins on twigs; gummy exudate at base of flowers; brown spore masses on flowers in humid conditions.
Cause
Fungi
Comments
Fungi survive in mummified fruit and dead twigs.
Management
2-3 fungicide applications are required during bloom to control disease; application very important at red bud stage; applications should be made every 14 days or less if there is continued heavy rainfall.

Jacket rot
Botrytis cinerea
Sclerotinia sclerotiorum
Monilinia laxa
Monilinia fructicola

Symptoms
Brown discoloration of fruit under jacket occurring while flower parts still attached to fruit
Cause
Fungi
Comments
Disease emergence favored by wet conditions during bloom and jacket stage
Management
Fungicide treatment applied at full bloom

Powdery midew
Sphaerotheca pannosa
Podosphaera tridactyla

Symptoms
Round powdery white patches of fungal growth on fruits and leaves; rusty patches on fruits which turn brown and leathery and may crack
Cause
Fungi
Comments
S. pannosa infects plant in Spring. P. tridactyla infects plant in Summer and Fall
Management
Apply fungicide during bloom and fruit development

Ripe fruit rot
Monilinia fructicola
Monilinia laxa

Symptoms
Dark brown circular spots on fruit; tan spore masses may be visible in center of spots; diseases fruit may not drop from tree
Cause
Fungi
Comments
Fruit rot symptoms will appear within 48 hours of rain
Management
A protective fungicide treatment may be necessary if heavy rains are forecast 2-3 weeks prior to harvest

Armillaria root rot
Armillaria mellea

Symptoms
If tree is infected after it has reached 5 years of age then typical symptoms include poor terminal growth and small leaves; around midsummer the whole tree suddenly collapses; in orchards trees usually die in a circular pattern; infected trees often have a fan-shaped white fungal mat growing between the bark and wood of the crown.
Cause
Fungus
Comments
Fungus survives in dead roots; symptoms similar to Phytophthora root rot.
Management
Once a tree is infected there is no treatment and it should be removed, fumigants do not control fungi in soil adequately; do not plant apricot in newly cleared forest or on the site of old orchards with a history of Armillaria.

Eutypa dieback
Eutypa lata

Symptoms
Cankers on branches, usually associated with a pruning wound which is several years old; discolored sapwood may extend abovwe and below canker; leaves on branches around canker may suddenly wilt as branch dies; leaves remain attached to branches; discoloured bark and inner wood; gummy amber exudate may be present.
Cause
Fungus
Comments
Fungus enters fresh pruning wounds with rainfall 2-6 weeks after pruning; emergence of disease most common in Fall or Winter.
Management
Infected limbs should be removed 1 ft below any internal symptoms before harvest; if pruning is conducted outwith this time a fungicide should be applied to the pruning wounds.

Shot hole disease
Wilsonomyces carpophilus

Symptoms
Brown lesions with purple edge on fruit, twigs and buds; holes in leaves due to lesions which have dried and dropped out; brown lumps developing in the center of lesion (visible with hand lens); buds turning brown or black and exuding sap; tan lesions with brown margins which exude sap on twigs.
Cause
Fungus
Comments
Fungus survives in buds and twigs; spores spread by water splash.
Management
Application of Bordeaux mixture before rains in Fall are sufficient to protect dormant buds and twigs over winter.

Verticillium wilt
Verticillium dahliae

Symptoms
Withering of leaves on one or more spurs on 1 year old wood; leaves are dull and stunted; fruit small; older cherry trees do not recover from disease
Cause
Fungus
Comments
Fungus survives in soil or in debris from other susceptible plants
Management
Plant apricot in soil with no history of disease; keep trees adequately fertilized and watered

Rust
Tranzschelia discolor

Symptoms
Pale yellow-green spots on both upper and lower leaf surfaces which are angular in shape and turn bright yellow in color; spots on lower leaf surface develop orange-red spores.
Cause
Fungus
Comments
Fungus overwinters in twigs or in leaves which remain attached to the tree.
Management
Rust can be prevented by spraying trees with protective fungicides; application is usually carried out one, two and three months before harvest in areas prone to early season outbreaks of the disease and after harvest in areas where disease is less problematic or emerges later in the season.

European earwig
Forficula auricularia

Symptoms
Mature trees generally tolerate damage well; if damage is caused to shoot tips of young trees then growth may be stunted; shallow, irregularly shaped areas may be present on fruit surface where insect has fed; insects are brown and shiny with a pincer-like structure at the end of the abdomen; can reach 1.3 cm (0.5 in) in length.
Cause
Insect
Comments
Earwigs are nocturnal and generally undergo two generation per year.
Management
Remove all weeds from around tree bases; remove all pruning debris and loose bark around trees; wrapping trunks tightly with plastic wrap before nymphs emerge can stop them climbing up the tree; if using insecticide, apply early in Spring when earwigs begin to be active.

Fruittree leafroller
Archips argyrospila

Symptoms
Leaves of plant rolled and tied together with silk webbing; feeding damage to rolled leaves; defoliation of plant; silk webbing may also be present on fruits and fruits may have substantial scarring from feeding damage; larvae wriggle vigorously when disturbed and may drop from plant on a silken thread.
Cause
Insect
Comments
Only one generation of insect per year.
Management
Monitor plants regularly for signs of infestation; remove weeds from plant bases as they can act as hosts for leafrollers; avoid planting pepper in areas where sugarbeet or alfalfa are grown nearby; Bacillus thuringiensis or Entrust SC may be applied to control insects on organically grown plants; apply sprays carefully to ensure that treatment reaches inside rolled leaves.

Green fruitworm
Various

Symptoms
Large holes chewed in leaves and fruit; pale green caterpillars with white stripe down middle of back present on leaves and fruit.
Cause
Insect
Comments
Insect usually overwinters as adult moth and undergoes only one generation per year.
Management
If larva become damaging to trees then sprays of Bacillus thuringiensis will control young larvae effectively and can be applied during bloom; other organically acceptable control methods include application of Entrust; appropriate insecticides can be used as spot treatments if infestation is localized or applied shortly before, or during, petal fall.

Mealy plum aphid
Hyalopterus pruni

Symptoms
High levels of infestation may cause stunted vegetative growth; black soot mold developing on leaves and branches; insect is small and soft-bodied, green in color and covered in white, mealy wax.
Cause
Insect
Comments
Infestations usually appear in small pockets in orchards; insect eggs overwinter and hatch in Spring.
Management
Organically grown trees can be sprayed with neem oil to control aphid populations; chemical control of the aphid is rarely necessary.

Peach twig borer
Anarsia lineatella

Symptoms
Death of shoot tips; feeding damage to fruit, usually at stem end; larvae are dark brown and white with a black head; adult insect is a gray-brown moth.
Cause
Insect
Comments
Peach twig borers overwinter as larvae in a specialized cell known as a hibernaculum; overwintering sites are located in rough areas of bark on 1 to 4 year old wood in crotch of limbs.
Management
Most effective method of treatment is well-timed applications of insecticide around time of bloom; organically acceptable insecticides include Bacillus thuringiensis or Entrust; infestations can also be treated with appropriate organophosphate or pyrethroid insecticides.

Phytophthora root and crown rot
Phytophthora spp.

Symptoms
Poor new growth; leaves chlorotic, small in size and sparse; fruit may be small, brightly colored and susceptible to sunburn; shoots may suffer from dieback and tree will often die within weeks or months of first signs of infection or decline gradually over several seasons; root crown may show signs of decay which develops into a canker; bark of infected crown tissue turns dark brown; cankers may occur on aerial parts of plant.
Cause
Oomycete
Comments
Severity of disease is linked to soil moisture content; water-saturated soils promote development of fungus.
Management
Plant trees on a small mound to promote drainage; avoid over-watering trees in spring; treat soil around newly planted trees with fungicide; minimize the frequency and duration of water saturated soil; trees should be propagated from resistant rootstock and application of appropriate systemic fungicides may provide some protection from the disease.

Plum pox virus
Plum pox virus (PPV)

Symptoms
Pale green chlorotic spots, rings and lines on leaves which appear in early summer; pale rings, lines and spots on fruit; fruit flesh dry and flavorless; fruit may be markedly deformed.
Cause
Virus
Comments
Virus is transmitted by aphids but most common method of spread is diseased plant material.
Management
Plant certified healthy material; remove infected trees from orchard; chemical sprays to control aphids may prolong spread of virus.