Apple

Malus domestica

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Description

Apple, Malus domestica, is a deciduous tree in the family Rosaceae which is grown for its fruits, known as apples. Apple fruits are one of the most widely cultivated fruits in the world, are round (pome) in shape and range in color from green to red. When planted from a seed, an apple tree can take six to ten years to mature and produce fruit of its own. Apple trees are small to medium sized trees reaching heights of 5–10 m (16.4–32.8 ft), with a central trunk which divides into several branches. The leaves of the tree are oval in shape and can reach up to 13 cm (5.1 in) in length and 7 cm (2.8 in) in width. Apple may also be referred to as mela or appel and the domestic tree is believed to have originated from Western Asia and the Mediterranean from several wild ancestors.

Uses

Apples are most commonly eaten fresh but can also be used for baking and cooking. Apples can also be processed into apple sauce, cider, vinegar, juice or butter while slices can be dried for later consumption. Apples can also be used for the extraction of useful compounds such as fructose and pectin

Propagation

Apple trees grow best in the tropics and at higher latitudes they require a mild growing season and a cold winter to break their dormancy. At these latitudes, the tree will flower in spring and fruit will ripen in the fall. In the tropics, the leaves will remain on the tree longer so that it is essentially evergreen and flowering and fruiting will happen sporadically throughout the year unless the tree is managed to enforce a uniform cycle across the entire tree by bending shoots to create a wide tree.

The standard method of propagating apple is by budding. When planting an apple nursery or orchard it is highly advisable to plant seedlings budded from root stock to prevent an increase in dormancy of the buds. Budded trees should be pruned in the first year to encourage new shoot growth.

In the tropics, apple trees require careful management in order to make the heavy crop loads sustainable. This includes bending shoots, pruning the tips and also defoliating the trees. Flowers are also removed to promote growth until the first fruit production, generally after 2 years.

Apple trees can also be propagated by grafting and mound layering. Grafting involves joining the lower part of one plant (root stock) with the upper part (scion) of another. Grafting is usually done during the dormant season and must be done on dormant scion and stock wood. Mound layering is used to propagate apple clonal root stocks. Soil is mounded around shoots that have been cut back, thereby stimulating roots to grow at the base of the shoots. A year before propagation begins, 8–10 mm (0.3–0.4 in) diameter stock plants are planted in rows and then cut back to 45–60 cm (17.7–23.6 in). They are then grown for one year. In the spring, the plants are again cut back, this time to 2.5 cm (1 in) above the ground. New shoots gradually form and more soil and bark are added in mounds around the plants. This cycle can continue on through the growing season. Then the shoots are harvested by cutting close to the bases. The mother stool beds are then left exposed until further growth of the new shoots has occurred, and another cycle of hilling begins.

Diseases

Aphids (Green apple aphid, Woolly apple aphid) Insects Aphis pomi
Eriosoma lanigerum

Symptoms

Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, woolly apple aphids are covered in masses of white, wool-like material; green apple aphids are dark green when they forst hatch and change to yellow-green with darker green spots as they mature; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants

Comments

Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed

Management

If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use

Apple maggot Insect Rhagoletis pomonella

Symptoms

Misshapen, pitted and sunken areas on fruit surface; browning and rotting of apple flesh

Comments

Surface damage caused to fruit by female laying her eggs; larvae damage flesh by burrowing and feeding

Management

Use red spherical sticky traps to trap adults, place one trap for every 100 apple fruits; bag apples by tying or stapling polythene bags around fruit to prevent adults laying eggs - cut corners from bags to ensure air supply to fruit; spray fruit with insecticide prior to eggs being laid

Apple scab Fungus Venturia inaequalis

Symptoms

Yellow or chlorotic spots on leaves; dark olive green spots on leaves and fruit; may be a velvety growth on spots on undersides of leaves; twisting of leaves; distorted leaves; severely infected leaves turn yellow and drop from tree

Comments

Fungus overwinters on dead foliage on ground; spores dispersed by wind; high moisture encourages fungal growth

Management

Remove all leaves dropped from tree in the fall and compost to prevent any diseases surviving in debris; application of zinc and fertilizer grade urea in the Fall may be necessary to speed leaf drop, lime should then be added to fallen leaves; fungicide application may be necessary in areas where leaves remain wet for periods in excess of 9 hours; fungicides such as copper soaps and Bordeaux mixture should be applied if there is a chance of wet period as soon as leaf tips emerge

Black rot Fungus Botryosphaeria obtusa

Symptoms

Purple flecks or circular lesions which are brown in the centre and purple at margin; red flecks, purple lesions and/or brown black rings on fruit

Comments

Spores can overwinter in twigs or fruit remaining on the tree and spread during rainfall

Management

Remove dead wood, mummified fruit and cankers from trees to reduce spread of disease; burn any prunings that have been made from the tree; disease can be controlled by applying fungicides from silver tip to harvest

Cedar apple rust Fungus Gymnosporangium juniperi-virginianae

Symptoms

Bright orange or yellow patches on top side of leaves surrounded by a red band and small black spots in the center; by mid-summer, cup-like structures called aecia form on the leaf undersides; these become covered in tubular structures from which spores are released

Comments

Fungus requires two hosts to complete lifecycle; forms galls on Eastern red cedar and spores are carried by wind to apple; use caution when planting apple close to red cedar.

Management

Plant resistant varieties where possible; remove nearby red cedar; if growing susceptible varieties in proximity to red cedar follow a fungicide program

Codling moth Insect Cydia pomonella

Symptoms

Holes and burrows in fruit; holes may be blocked with crumbly brown frass (insect excrement); wounds may be shallow or may be deep burrows extending to the fruit’s core; adult insect is a dark brown moth; larvae are pink with a brown head and may be up to 1.3 cm (0.5 in) long

Comments

Insect usually undergoes 2-4 generations per year

Management

Proper pruning methods help to open out tree canopy to ensure treatments penetrate interior of the tree and reach larvae; removal of any wild hosts or trees in abandoned orchards helps remove reservoirs of insect; organically acceptable control methods include application of Entrust and kaolin clay; small scale growers and home gardeners can remove infested fruit by hand before larvae leaves fruit to reduce insect population; successful reduction of insect population in large scale orchards is usually achieved by mating disruption by releasing pheromones over successive years

Fire blight Bacterium Erwinia amylovora

Symptoms

Plant appears as if it has been scorched by fire; watery exudate may be present on infected areas

Comments

Bacterium overwinters in bark or cankers; spread by pollinating insects and by rain splash

Management

Cut out diseased wood; treat with Bordeaux mixture or approved fixed copper materials for organic production; streptomycin or copper application to blossoms may be necessary to prevent spread

Flyspeck Fungus Zygophiala jamaicensis

Symptoms

Shiny black fungal fruiting bodies appear as dots arranged in irregular to circular pattern on fruit surface

Comments

Outbreaks usually follow above average summer temperatures and frequent rainfall

Management

Prune trees to open canopy and promote drying of fruit surface; fungicides may be applied as a preventative measure

Leafhoppers (White apple leafhopper, Rose leafhopper) Insect Typhlocyba pomaria
Edwardsiana rosae

Symptoms

White stippling on foliage; may be a reduction in fruit size; black specks of frass on fruit; sticky exudate on fruit and leaves caused by excretion of honeydew by insect

Comments

Damage resembles that of spider mites but is much more noticeable; insect usually reaches highest number close-to or after harvest

Management

Control of leafhoppers is becoming problematic as they are developing resistance to organophosphate insecticides; sprays of appropriate insecticides are most effective at controlling the insect before the adults emerge; monitor trees for appearance of nymphs

Leafrollers (Omnivorous leafroller, Redbanded leafroller, etc) Insect Platynota stultana
Argyrotaenia velutinana

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

Comments

Adult insect is a moth which can fly over several miles to find suitable hosts

Management

Monitor plants regularly for signs of infestation; remove weeds from plant bases as they can act as hosts for leafrollers; 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

Phytophthora crown and root rot Fungus Phytophthora spp.

Symptoms

Leaves wilting but remain attached to the tree; reduced growth; early senescence; cankers at soil level, dark discoloration of bark which is slimy when wet

Comments

Infection encouraged by poorly draining soil.

Management

Practice good water management to prevent emergence of disease; do not over-water trees or allow water to accumulate in soil; there is no treatment for Phytophthora infection once present; no apple varieties are resistant to all strains of the pathogen

Powdery mildew Fungus Podosphaera leucotricha

Symptoms

White velvety patches on underside of leaves; chlorotic spots on top side of the leaves

Comments

Fungal spores overwinter in buds; spread by wind

Management

Prune out infected shoots while dormant in early spring; apply sprays at pink bud stage to reduce build up; organic treatments include application of lime and sulfur

Sooty blotch and flyspeck Fungi Caused by a complex of Leptodontium elatius, Peltaster fructicola and Geastrumia polystigmatus

Symptoms

Sooty blotches with an indefinite margin on surface of fruit; blotches may coalesce to cover entire fruit; shiny black fungal fruiting bodies appear as dots arranged in irregular to circular pattern on fruit surface

Comments

Infections occur mainly during periods of high rainfall and high humidity

Management

Plant trees in area with good sunlight and air circulation; prune trees to an open center; blemishes superficial and can be washed off

Spider mites Arachnid Tetranychus urticae

Symptoms

Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant

Comments

Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack

Management

In the home garden, spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction

Stinkbugs (Various) Insect Various

Symptoms

Dark colored pinpricks on fruit; depressed dimples on fruit surface with white, pithy area underneath; stink bugs often carry pathogens in their mouthparts which can cause secondary infections and decay of fruit; adult insect is shield-shaped and brown or green in color; may have pink, red or yellow markings; eggs are drum shaped and laid in clusters on the leaves; larvae resemble the adults but are smaller; insect frass may be visible on the fruit is small, brown teardropped shaped deposits

Comments

Adult insects overwinter under leaves, on legumes, blackberries or on certain weeds such as mustard or Russian thistle

Management

Remove weeds around crop which may act as overwintering sites for stink bugs and practice good weed management throughout the year; organically accepted control methods include the use of insecticidal soaps, kaolin clay and preservation of natural enemies

References

CABI Crop Protection Compendium. (2013). Malus domestica datasheet. Available at: http://www.cabi.org/cpc/datasheet/31964. [Accessed 05 November 14]. Paid subscription required

Peck, G. M. & Merwin, I. A. (Eds) (2009). A Grower's Guide to Organic Apples. Cornell Cooperative Extension. Available at: http://nysipm.cornell.edu/organic_gui.... [Accessed 05 November 14]. Free to access

Polomski, B. & Reighand, G. (2007). Home and Garden Information Center: Apple. Clemson Extension. Available at: http://web.archive.org/web/2006090711.... [Accessed 05 November 14]. Free to access

Sutton, T. B., Aldwinckle, H. S., Agnello, A. M. & Walgenbach, J. F. (Eds.) (2014). Compendium of Apple and Pear Diseases and Pests. 2nd Edition. American Phytopathological Society. APS Press. Available at: http://www.apsnet.org/apsstore/shopap... Available for purchase from APS Press

Warmund, M. (2014). Home fruit production: apples. University of Missouri Extension. Available at: http://extension.missouri.edu/explore.... [Accessed 05 November 2014]. Free to access