Papaya (pawpaw)

Description

Papaya, Carica papaya, is an herbaceous perennial in the family Caricaceae grown for its edible fruit. The papaya plant is tree-like,usually unbranched and has hollow stems and petioles. The leaves are palmately lobed, spirally arranged and clustered at the growing tip of the trunk. Papaya trees can be male, female or hermaphrodite and the type of inflorescence produced is reflective of this. Male trees produce many flowers on long, pendulous panicles while female trees produce either solitary flowers of clusters of a few flowers which are yellow-green in color. Hermaphrodite trees produce bisexual flowers. The papaya fruit is a large fleshy berry with smooth green skin that ripens to yellow or orange. The flesh of the fruit is thick and succulent and ranges in color from yellow to red or orange. The fruit contains many black wrinkled seeds. Papaya trees range in height from 2–10 m (6.6–33 ft) and can live for up to 25 years. Plantations are usually replaced every 3 years to ensure maximum productivity. Papaya may also be referred to as pawpaw and is believed to originate from the Caribbean region on Central America.


Uses

Papaya fruits are commonly eaten fresh. The may also be processed into jams, jellies and juices are dried and candied. Green fruits and young leaves can be cooked and eaten as a vegetable.


Propagation


Basic requirements
Papaya is a tropical plant and will grow optimally at temperatures between 21 and 33°C (69.8–91.4°F) in areas with no frost. Papaya can be grown in a range of soils as long as there is adequate drainage but will grow optimally in light, well-draining soils with a pH between 5.5 and 6.5. Papaya requires well distributed rainfall of about 4 inches per month. In areas with low rainfall, trees should be provided with supplemental irrigation. Trees are very sensitive to flooding and water-logged soils should be be avoided. Papaya is also sensitive to high winds and the tall trees can be easily toppled. Windy areas should be avoided for planting.

Propagation
Papaya is propagated from seed due to the labor involved in producing cuttings. Seeds are usually sown in small containers or nursery beds in sterilized soil. It is usual to sow 3–4 seeds per container and seeds can take 3–4 weeks to germinate depending on temperature.. Seedlings are transplanted after approximately 2 months when the reach approximately 20 cm (8 in) in height and possess 3–4 leaves. Seedlings are commonly planted on hills or ridges to aid drainage and should be spaced 2–3 m (6.6–9.8 ft) apart.

General care and maintenance
Papaya seedlings are very susceptible to competition from weeds and the areas around the trees should be kept weed-free. A layer of mulch around the plants can successfully suppress weeds. Papaya requires regular fertilizer applications to meet the nutrient requirements for fruit production. In commercial plantations, fertilizer is usually applied 2–4 times per year. In the home garden, the addition of 1/4 cup of a balanced fertilizer every 14 days is usually sufficient. As the trees mature, the amount of fertilizer should be increased. When trees reach 7 to 8 months, 1–2 lbs of a complete fertilizer should be provided every 2 months. Papaya trees should be watered regularly, particularly during hot, dry periods. Papaya trees do not require pruning but it is good practice to remove any dead leaves from the tree.

Harvesting
Papaya fruits generally require 22–26 weeks to mature. The fruits can be picked when 1/5 of the fruit surface has turned from green to yellow but leaving them on the tree longer will increase the sugar content of the fruit. Fruit can be twisted or snapped from the tree or cut using a sharp knife.



References

CABI Crop Protection Compendium. (2008). Carica papaya (papaw) datasheet. Available at: http://www.cabi.org/cpc/datasheet/13392. [Accessed 03 March 15]. Paid subscription required.

Crane, J. H. Papaya growing in the Florida home landscape. University of Florida IFAS Extension. Available at: https://edis.ifas.ufl.edu/pdffiles/MG.... [Accessed 03 March 15]. Free to access.

Nishina, M., Zee, F., Ebesu, R., Arakaki, A., Hamasaki, R., Fukuda, S, Nagata, N., Chia, C. L., Nishijima, W., Mau, R. & Uchida, R. (2000). Papaya production in Hawaii. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Available at: http://www2.ctahr.hawaii.edu/oc/freep.... [Accessed 03 March 15]. Free to access.

Ploetz, R. C., Zentmyer, G. A., Nishijima, W. T., Rohrbach, K. G. & Ohr, H. D. (eds) (1994). Compendium of Tropical 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 and decline
Erwinia spp.

Symptoms
Angular water-soaked lesions on leaves; lesions coalesce and spread along leaf veins; witling leaves, particularly at top of canopy; water-soaked lesion and cankers on stem; cankers girdle stem and cause plant to collapse; small water-soaked lesions on green fruit.
Cause
Bacteria
Comments
Bacteria survive in lesions and cankers.

Bunchy top
Likely caused by Rickettsia bacteria

Symptoms
Chlorosis of young leaves; water-soaked spots on petioles and stems; petioles rigid, horizontal and shortened; thickened leaf blades that cup downward; internodes shorten and growth stops resulting in a bunchy appearance to the plants.
Cause
Bacteria
Comments
Transmitted by leaf hoppers.
Management
Use of tolerant varieties of papaya is currently the only method of control recommended.

Internal yellowing
Enterobacter cloacae

Symptoms
Flesh of ripe fruit discolored yellow; discolored areas soft with spreading margins; rotting odor.
Cause
Bacterium
Comments
Disease found in Hawaii.
Management
Dipping fruits in hot water at 48°C for 20 minutes reduces the incidence of the disease and is currently the only method of control.

Anthracnose and charcoal spot
Colletotrichum gleosporoides

Symptoms
Small water-soaked lesions of fruit during ripening; circular sunken lesions with light brown margins.
Cause
Fungus
Comments
Fungi spread by wind and rain; disease emergence favored by high temperature and humidity; disease can have a serious impact on refrigerated fruit for export.
Management
Appropriate protective fungicides should be applied; dipping fruits in hot water at 48°C for 20 minutes reduces the incidence of the disease.

Black spot
Asperisporium caricae

Symptoms
Circular water-soaked or brown lesions on older leaves; centers of lesions become bleached as they mature; leaves curling and turning brown; raised lesions on trunks; sunken circular lesions on fruit.
Cause
Fungus
Comments
Disease spread by wind and rain; disease emergence favored by cool weather interspersed with moisture from dew or rain.
Management
Disease may require applications of appropriate fungicides for adequate control.

Black rot
Mycosphaerella caricae

Symptoms
Black sunken rot on young fruits originating from stem end or contact with a leaf; young fruit withering and dropping from plant; small, brown sunken lesions with light brown margins on ripening fruit.
Cause
Fungus
Comments
Fungi enters fruit through wounds.
Management
Appropriate protective fungicides should be applied; dipping fruits in hot water at 48°C for 20 minutes reduces the incidence of the disease.

Cercospora black spot
Cercospora papayae

Symptoms
Tiny black dots on fruit which enlarge to 3 mm across; spots are slightly raised and although indistinct on unripe green fruit, become visible on ripening to yellow; lesions on leaves are irregular in shape and gray-white in color; if infestation is severe, leaves may turn yellow and necrotic and drop from plant.
Cause
Fungus
Comments
Disease usually enters orchard from infected papaya leaves in adjacent orchards.
Management
Applications of appropriate protective fungicides at intervals of 14 to 28 days provide satisfactory control of the disease.

Powdery mildew
Oidium caricae-papayae
Other fungi species

Symptoms
Infect all parts of tree. The infected leaves show white mycelial growth commonly on under surface , particularly near leaf veins. Some time white mycelial growth can also seen on upper leaf surface. The infected area becomes light green and chlorotic (lesions) with dark green margin.
Cause
Fungus
Comments
Powdery mildew pathogens are saprophytic need living host for survival and growth. The pathogen is favored by high humidity and low sunlight.
Management
Remove the infected parts and dispose them properly. Avoid irrigating the trees by sprinkler. Provide proper nutrition to trees to withstand powdery mildew infection. If the disease is severe, apply suitable fungicides.

Papaya mealybug
Paracoccus marginatus

Symptoms
Flattened oval to round disc-like insect covered in cottony substance on tree; chlorosis, plant stunting, leaf deformation, early leaf and fruit drop insects attract ants which may also be present; insect colony may also be associated with growth of sooty mold due to fungal colonization of sugary honeydew excreted by the insect.
Cause
Insect
Comments
Insects have a wide host range; often tended by ants which farm them for their sugary honeydew secretions; transmit Cocoa swollen shoot virus.
Management
Mealybugs can potentially be controlled by natural enemies such as lady beetles but are commonly controlled using chemicals; chemical pesticides may also decrease populations of natural enemies leading to mealybug outbreaks.

Scale insects (White peach scale)
Pseudaulacaspis pentagona

Symptoms
Scale insects cause damage by feeding on twigs, branches and fruit, injecting toxins into the plant as they do so; if the infestation is heavy, gumming may occur on the bark and twigs or entire branches can be killed; insects are flattened discs, or "scales" with no visible legs; scales produce a white waxy coating which eventually turns black (black cap stage).
Cause
Insect
Comments
Scale insects overwinter in the black cap stage; winged adult males mate with females which retain their eggs inside the body until they hatch.
Management
Populations are often kept in check by natural enemies, including predacious beetles and some wasps - although broad-spectrum insecticides may result in outbreaks of scale by killing off populations of beneficial insects; trees can be sprayed with horticultural oils when dormant which effectively kill scales without damaging natural enemies.

Phytophthora fruit rot (Stem rot)
Phytophthora palmivora

Symptoms
Water-soaked lesions on unripe fruit that oozes latex; withering fruit; water-soaked lesions on leaf scars of fruit bearing stem; mature fruit covered in white mycelium.
Cause
Oomycete
Comments
Fungi survive in soil and enter through wounds in stem; disease often emerges after hurricane damage.
Management
Disease can be controlled through the use of appropriate protective fungicides such as mancozeb or copper sulfate; root rot in seedlings can be prevented by planting in holes filled with soil in which papaya has never been grown - by the time the roots extend out of the added soil the plant is no longer susceptible to the disease.

Papaya ringspot
Papaya ringspot virus (PRV)

Symptoms
Dark green rings on fruit which may be slightly sunken and become less distinct as the fruit ripens; fruits may have uneven bumps; leaves often exhibit a bright yellow mosaic pattern and new leaves are small and plant growth is stunted.
Cause
Virus
Comments
Virus is transmitted by several aphid species.
Management
Infected plants should be removed and destroyed to prevent spread of the virus; new planting materials should be free of the virus; intercropping papaya with a non-host such as corn can help to reduce the incidence of the disease in papaya orchards by providing aphid vectors with an alternative feeding site.