Common Pests and Diseases and their Control
Mites – Under local conditions, the red spider mites (Tetranychus kanzawai Kishida) is most common attacking and severely damaging the older leaves of papaya and sometimes attacking its seedlings. Its serious damage causes the leaves to dry up, thus, reducing the photosynthetic activity of the plant.
Control Measures – To prevent the sources and build up of mite population, leaf pruning and burning of damaged and attacked leaves are done weekly. For chemical control, use selective miticides sprayed at 7 to 10 days interval.
Scale insects – The most common scale insects species colonizing and feeding on papaya fruit is the Aspidiotus destructor Sig. Their feeding caused the fruit to ripen prematurely and destroy the external appearance of the fruits.
Control Measures – Spray recommended insecticide to control incidence of scale insects in the fruits. Spraying should be done directly to the fruits 15 days before harvest. Adjust spray nozzle so as not to hit harvestable fruit in case there are available harvestable fruits. Re-spray 7 days after if presence of such pest is still visible.
Fruit Fly – Dacus dorsalis and Dacus cucurbitae Coq. are species of fruit fly attacking papaya. When an outbreak in population occurs, the eggs are deposited in the ripening fruits while they are still attached to the tree. Harvested fruits eventually rot as the newly hatched larvae start to feed inside the fruit.
Control Measures – Sanitation inside the population is essential by gathering all ripened, damaged and fallen fruits. Gathered fruits should be dumped in pit and burned. Use Methyl Eugenol to attract male files and kill them. Do not allow ripe fruits to remain in the tree for sometime.
Damping off – Symptoms:
Tissues of the papaya seedling stems at the solid line become water-soaked and rotten due to infection by one or more species of fungi-like Pithium debayranum, Pytopthora palmivora and Rhizoctonia sp. It is common in the nursery or in the field where seedlings are too crowded. It is favored by high temperature and wet weather.
Control Measures – Avoid overcrowding of seedlings. Provide good drainage and adequate soil erosion. Practice proper plant spacing and depth of planting.
Papaya mosaic – Symptoms:
Leaves of infected plants develop a wrinkled and rough appearance. Younger leaves are generally stunted and chlorotic and are accompanied by vein-banding or transparent oil that are scattered over the leaf veins. Older and mature leaves show more pronounced chlorotic areas and are stunted. Severe attack results in stunting of petioles.
Infected young fruit shows small, dark green spots, which appear either on the stem or blossom end. They enlarge as the fruit develops. Mottling of green and brownish rings appear.
Control Measures – Cut down infected plant and burn.
Bacterial Crown Rot – Diseased papaya are really distinguished in the field by the dropping leaves which results from infection of the petiole or stem with the bacterium Erwina cariceae.
Symptoms – Initial symptoms found on the petiole and stem are water-soaked spots. The spots rapidly enlarged causing rotting of the petiole or stem. Then the crown droops and wilts showing leaf yellowing it may topple-over.
Young, soft plant parts are susceptible to infection with the bacterium gaining entry through natural openings and wounds. In susceptible cultivars, infection becomes systematic causing vascular discoloration of the stem, fruits and roots. The disease is common during periods of prolonged wetness or continuous rainfall. Infected plants may recover and produce productive branches during dry season.
Control measures – Eradicate severely infested plants and disinfect tools with 10% formalin solution. In cases when the stem is not infected, remove only the infected petioles and leaves. Provide protection to the papaya plants during rainy periods by spraying crown (petioles, leaves, fruit and young stem) with copper fungicide at 3 g/li. of water once every 14 days.
Anthracnose – The disease is caused by Collectrichum gleosporiodes and effects not only the fruits but also petioles of older leaves.
Symptoms – Small, round, water-soaked areas appear on infected ripened portion of the fruits. Fungus produces pink spore masses, which appear in concentric rings in the lesions. Fungus also penetrates into the tissues of the fruit, causing it to become darker and softer than the surrounding tissues. Infected portion have unpleasant flavor. On green parts, it appears as small, water-soaked lesions oozing out from the infected areas.
Control Measures – Spray with recommended fungicide plus a spreader sticker to ensure good spray coverage at 7-10 days interval. Post harvest storage decay can be reduced by treating fruits in hot water at temperature of 110-120?F for 20 minutes.
Pythoptora rot – Symptoms:
Seedling damps-off, root rots, trunk cankers and fruit rots. Immature fruits are attacked through wounds while mature fruits at any location.
Control Measures – Remove infected fruit and dispose properly. Spray copper fungicide at recommended rate. (For fruits in storage, control by hot water dips at 46.7?F for 20 minutes then cool with running tap water.)
Papaya Ringspot Virus – The Papaya Ringspot Virus (PRSV) is readily transmitted mechanically by sap. It is also stylet born and insect transmitted by aphids. It is not readily transmitted through seeds.
Symptoms – Vein clearing, mottling and the presence of yellow spots are the initial symptoms of the leaf. Later, the leaves are reduced in size and margins tend to curls upward and downward. Dark green concentric rings or green spots appear on fruits and the disease progresses, fruit set is sharply deformed and smaller.
Control Measures – Eradication of infested plants and spraying the infected and the apparently healthy tree surrounding it with appropriate insecticide before uprooting and chopping the infected trees to small pieces. Place the chopped plant debris in a sack or plastic bag and burn it in a suitable place.
Never intercrop papaya trees with possible alternate host such as watermelon, cucumber, squash, etc. Enforce quarantine measures prohibiting the transfer and introduction of papaya and alternate hosts from affected orchards to new growing areas. Use resistant papaya cultivars.
Harvesting and Post Harvest Management
Papaya generally starts to flower after 5 months from seedling and the first harvest is obtained 4 to 5 months later. When intended for vegetable, papaya can be harvested when fruit is at color break to ripe. For shipping to distant market the fruits should be harvested when the apical end starts turning yellow and the latex is no longer milky. Do not allow fruits to ripen on the plant and they should not be dropped to the ground to avoid possible injuries. Use step ladder or plumber helper with long bamboo pole to pick the fruits if the tree grows taller.
To harvest, to twist the fruit until its stalk snaps off the plant or cut the stalk with sharp knife.
The productive lifespan of papaya gradually ends on the 3rd or 4th year. As the tree matures, production also slackens. The yield of well-managed papaya plantation is 35 to 40 tons per hectare.
A good method of packing is to place the fruits in single layer in a rectangular wood container lined with dried banana leaves or shredded newsprint to protect the fruit against the normal hazards of transport and handling.
Ripe papayas may be stored at 8.3 C and partially ripe ones at 11.9 C. At these temperatures, the fruit can be kept for 3 weeks. To avoid chilling injury which is manifested by impaired ripening, do not store less mature fruit below 7.1 C.
The papaya is regarded as a fair source of iron and calcium; a good source of vitamins A, B and G and an excellent source of vitamin C (ascorbic acid). The following figures represent the minimum and maximum levels of constituents as reported from Central America and Cuba.
Ripe papayas are most commonly eaten fresh, merely peeled, seeded, cut in wedges and served with a half or quarter of lime or lemon. Sometimes a few seeds are left attached for those who enjoy their peppery flavor but not many should be eaten. The flesh is often cubed or shaped into balls and served in fruit salad or fruit cup. Firm-ripe papaya may be seasoned and baked for consumption as a vegetable. Ripe flesh is commonly made into sauce for shortcake or ice cream sundaes, or is added to ice cream just before freezing; or is cooked in pie, pickled, or preserved as marmalade or jam. Papaya and pineapple cubes, covered with sugar sirup, may be quick-frozen for later serving as dessert. Half-ripe fruits are sliced and crystallized as a sweetmeat.
Papaya juice and nectar may be prepared from peeled or unpeeled fruit and are sold fresh in bottles or canned. In Hawaii, papayas are reduced to puree with sucrose added to retard gelling and the puree is frozen for later use locally or in mainland USA in fruit juice blending or for making jam.
Unripe papaya is never eaten raw because of its latex content. [Raw green papaya is frequently used in Thai and Vietnamese cooking.] Even for use in salads, it must first be peeled, seeded, and boiled until tender, then chilled. Green papaya is frequently boiled and served as a vegetable. Cubed green papaya is cooked in mixed vegetable soup. Green papaya is commonly canned in sugar sirup in Puerto Rico for local consumption and for export.
Young leaves are cooked and eaten like spinach in the East Indies. Mature leaves are bitter and must be boiled with a change of water to eliminate much of the bitterness. Papaya leaves contain the bitter alkaloids, carpaine and pseudocarpaine, which act on the heart and respiration like digitalis, but are destroyed by heat. In Indonesia, the flowers are sometimes candied. Young stems are cooked and served in Africa. Older stems, after peeling, are grated, the bitter juice squeezed out, and the mash mixed with sugar and salt.
Studies at the University of Nigeria have revealed that extracts of ripe and unripe papaya fruits and of the seeds are active against gram-positive bacteria. Strong doses are effective against gram-negative bacteria. The substance has protein-like properties.
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sources: bpi.da.gov.ph, da.gov.ph, hort.purdue.edu