Horticulture/Malus

Malus is a genus of about 30-35 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated Orchard Apple, or Table apple as it was formerly called (M. sylvestris domestica, derived from M. sylvestris sieversii, syn. M. pumila). The other species and subspecies are generally known as "wild apples", "crab apples", "crabapples" or "crabs", this name being derived from their small and tart fruit. The genus is native to the temperate zone of the Northern Hemisphere, in Europe, Asia and North America.

Description
Apple trees are small, typically 4-12 m tall at maturity, with a dense, twiggy crown. The leaves are 3-10 cm long, alternate, simple, with a serrated margin. The flowers are borne in corymbs, and have five petals, which may be white, pink or red, and are perfect, with usually red stamens that produce copious pollen, and an inferior ovary; flowering occurs in the spring after 50-80 growing degree days (varying greatly according to subspecies and cultivar). Apples require cross-pollination between individuals by insects (typically bees, which freely visit the flowers for both nectar and pollen); all are self-sterile, and (with the exception of a few specially developed cultivars) self-pollination is impossible, making pollinating insects essential. The honeybee and mason bee are the most effective insect pollinators of apples. Malus species hybridize freely, so identification can sometimes be difficult.

The fruit is a globose pome, varying in size from 1-4 cm diameter in most of the wild species, to 6 cm in M. sylvestris sieversii, 8 cm in M. sylvestris domestica, and even larger in certain cultivated orchard apples; among the largest-fruited cultivars (all of which originate in North America) are 'Wolf River' and 'Stark Jumbo'. The centre of the fruit contains five carpels arranged star-like, each containing one to two (rarely three) seeds.

Malus trilobata, a species from southwest Asia, has three- to seven- lobed leaves (superficially resembling a maple leaf) and with several structural differences in the fruit; it is often treated in a genus of its own, as Eriolobus trilobatus.

Uses
Many consider crabapples unpalatable, but others enjoy eating them raw or using them for cooking or juicing. Cultivars such as 'Whitney' have been independently domesticated for better fruit quality.

For Malus sylvestris domestica, see Apple. The fruit of the other species is not an important crop in most areas, being extremely sour and (in some species) woody, and is rarely eaten raw for this reason. However, crabapples are an excellent source of pectin, and their juice can be made into a ruby-coloured jelly with a full, spicy flavour. A small percentage of crab apples in cider makes a more interesting flavour.

Crabapples are widely grown as ornamental trees, grown for their beautiful flowers or fruit, with numerous cultivars selected for these qualities and for resistance to disease.

Some crab apples are used as rootstocks for domestic apples to add beneficial characteristics. For example, Siberian crab rootstock is often used to give additional cold hardiness to the combined plant for orchards in cold northern areas.

They are also used as pollinators in apple orchards. Varieties of crab apple are selected to bloom contemporaneously with the apple variety in an orchard planting, and the crabs are planted every sixth or seventh tree, or limbs of a crab tree are grafted onto some of the apple trees. In emergencies a bucket or drum bouquet of crab apple flowering branches are placed near the beehives as orchard pollenizers. See also Fruit tree pollination.

Maintenance
Prune in early winter.

Propagation
Most cultivars are propagated by grafting or budding.

Pests and diseases
../Blight/ ../Powdery Mildew/ ../Leaf Spots/
 * ../Erwinnia amylovora/
 * Podosphaera leucotricha

../Scab/ ../Fruit Rot/
 * Venturia inequalis

../Brown Rots/

../Cankers/ ../Heart Rot/
 * Nectria galligena
 * Phoma mali
 * Physalospora obtusa

../Mushroom Root Rot/

../Rusts/ ../Bitter Pit/ (Calcium Deficiency)
 * ../Gymnosporangium juniperi-virginianae/
 * ../Gymnosporangium globosum/

../Bud Blast/ Caused by late freezes

../Aphids/ ../Scales/ ../Hoppers/ ../Psyllids/ ../Cicadas/ ../Whiteflies/
 * Cowpea Aphid: ../Aphis craccivora/
 * Wooly Apple Aphid: ../Eriosoma lanigerum/
 * Apple Grain Aphid: ../Rhopalosiphum fitchii/
 * Putnam Scale: ../Diaspidiotus ancyllus/
 * Calico Scale: ../Eulecanium cerasorum/
 * Greedy Scale: ../Hemiberlesia rapax/
 * European Fruit Lecanium Scale: ../Lecanium corni/
 * Oystershell Scale: ../Lepidosaphes ulmi/
 * San Jose Scale: ../Quadraspidiotus perniciosus/
 * Forbes Scale: ../Quadraspidiotus forbesi/
 * Buffalo Treehopper: ../Stictocephala bisonia/
 * White Apple Leafhopper: ../Typhlocyba pomaria/
 * Rose Leafhopper: ../Edwardsiana rosa/
 * Apple Sucker: ../Psylla mali/
 * Periodical Cicada: ../Magicicada septendecim/

../Mealybugs/ ../Bugs/ ../Earwigs/ ../Thrips/ ../Maggots/ ../Beetles/ ../Weevils/ ../Caterpillars/ ../Sawflies/
 * Taxus Mealybug: ../Dysmicoccus wistariae/
 * Comstock Mealybug: ../Pseudococcus comstocki/
 * Grape Mealybug: ../Pseudococcus maritimus/
 * Alder Lacebug: ../Corythucha pergandei/
 * Boxelder Bug: ../Leptocoris trivittatus/
 * Western Boxelder Bug: ../Leptocoris rubrolineatus/
 * Tarnished Plant Bug: ../Lygus lineolaris/
 * European Earwig: ../Forficula auricularia/
 * Western Flower Thrips: ../Frankliniella occidentalis/
 * Apple Maggot: ../Rhagoletis pomonella/
 * Western Cherry Fruit Fly: ../Rhagoletis completa/
 * Flatheaded Appletree Borer: ../Chrysobothris femorata/
 * Plum Curculio: ../Conotrachelus nenuphar/
 * Japanese Beetle: ../Popillia japonica/
 * Roundheaded Appletree Borer: ../Saperda candida/
 * Shothole Borer: ../Scolytus rugulosus/
 * Pacific Flatheaded Borer: ../Chrysobothris mali/
 * Rain Beetles: ../Pleocoma/ spp.
 * Redheaded Flea Beetle: ../Systena frontalis/
 * Tenlined June Beetle: ../Polyphylla decimlineata/
 * Asiatic Oak Weevil: ../Cyrtepistomus castaneus/
 * Whiteline Leafroller: ../Amorbia humerosana/
 * Snailcase Bagworm: ../Apterona helix/
 * Fruittree Leafroller: ../Archips argyrospila/
 * Io Moth: ../Automeris io/
 * Apple and Thorn Skeletonizer: ../Choreutis pariana/
 * Obliquebanded Leafroller: ../Choristoneura rosaceana/
 * Yellownecked Caterpillar: ../Datana ministra/
 * American Plum Borer: ../Euzophera semifuneralis/
 * Hickory Tussock Moth: ../Halisodota caryae/
 * Whitemarked Tussock Moth: ../Hemerocampa leucostigma/
 * Saddled Prominent Caterpillar: ../Heterocampa guttivitta/
 * Cecropia Moth: ../Hyalophora cecropia/
 * Fall Webworm: ../Hyphantria cunea/
 * Gypsy Moth: ../Lymantria dispar/ (syn. Porthetria dispar):
 * Eastern Tent Caterpillar: ../Malacosoma americanum/
 * Western Tent Caterpillar: ../Malacosoma californica/
 * Forest Tent Caterpillar: ../Malacosoma distria/
 * Speckled Green Fruitworm: ../Orthosia hibisci/
 * Western Tentiform Leafminer: ../Phyllonorycter elmaella/
 * Blackheaded Fireworm: ../Rhopobota naevana/
 * Redhumped Caterpillar: ../Schizura concinna/
 * Saddleback Caterpillar: ../Sibine stimulea/
 * Sparganothis Leafroller, Blueberry Leafroller, Cranberry Leafroller: ../Sparganothis sulfureana/
 * Dogwood Borer: ../Synanthedon scitula/
 * Apple Bark Borer: ../Synanthedon pyri/
 * European Leafroller: ../Archips rosanus/
 * Eyespotted Bud Moth: ../Spilonota ocellana/
 * Cherry Bark Tortrix: ../Enarmonia formosana/
 * Cherry Fruitworm: ../Grapholita packardi/
 * Oriental Fruit Moth: ../Grapholita molesta/
 * Pistol Casebearer: ../Coleophora malivorella/
 * Redbanded Leafroller: ../Argyotaenia velutinana/
 * Resplendent Shield Bearer: ../Coptodisca splendoriferella/
 * Leaf Crumpler: ../Acrobasis indigenella/
 * Lesser Appleworm: ../Grapholita prunivora/
 * Apple Pandemis: ../Pandemis pyrusana/
 * Variegated Leafroller: ../Platynota flavedana/

../Wasps/

../Mites/
 * Brown Mite: ../Bryobia rubrioculus/
 * Spider Mite: ../Oligonychus newcomeri/
 * European Red Mite: ../Panonychus ulmi/
 * Twospotted Spider Mite: ../Tetranychus urticae/

list of Lepidoptera which feed on Malus.