Introduction to Papaya pests, diseases, and their control procedure
Papaya is also known as pawpaw, is an important agricultural export. Papaya trees are tropical plants that produce pear-shaped and melon-like fruit. They can be difficult to grow as they’re sensitive to drought, cold temperatures, high winds, and shade. Also, they are susceptible to disease and can be damaged by chemicals used to treat diseases. Insufficient water, disease, or attack by nematodes can all cause Papaya trees to wilt. Now, let us get into the details of Papaya pests and diseases.
A step by step guide to Papaya pests, diseases, and control
Papaya is an herbaceous perennial in the Caricaceae family grown for its edible fruit. The papaya plant is tree-like, usually unbranched and hollow stems and petioles. The plant leaves are palmately lobed, spirally arranged, and clustered at the growing tip of the trunk. Papaya is a tropical fruit cultivated in frost-free areas throughout the world. Papaya has culinary, medical, and industrial uses, but is cultivated for its edible fruit. Diseases are important factors in reducing the yield and marketability of papaya.
Papaya is the delicious fruit grown widely under tropical and sub-tropical climates. The fruit has thin skin and thus rough handling leads to heavy losses due to several rots caused by fungi and bacteria. Commercial papaya production has been hampered worldwide due to the high susceptibility of the crop to different fungal, viral, and bacterial diseases. It is a tropical plant and will grow optimally at temperatures between 21 and 33°C 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 level between 5.5 and 6.5.
Papaya is mainly propagated from seed due to the labor involved in producing cuttings. Seeds are sown in small containers or nursery beds in sterilized soil. Papaya seedlings are susceptible to competition from weeds and the areas around the trees should be kept weed-free. A layer of mulch around the Papaya plants can successfully suppress weeds. Papaya requires regular fertilizer applications to meet the nutrient requirements for Papaya fruit production.
Papaya pests and diseases symptoms and their control
- Small water-soaked lesions on the Papaya fruit during ripening later becoming circular sunken lesions with light brown margins. The fungus is spread by wind and rain disease emergence is favored by high temperature and humidity. The disease can have a serious impact on refrigerated Papaya fruit for export.
- The Anthracnose disease prominently appears on green immature fruits. The Anthracnose disease symptoms are in the form of brown to black depressed spots on the fruits. The initial symptoms are water-soaked, sunken spots on the Papaya fruit. Then, the centers of these spots later turn black and then pink when the fungus produces spores. The flesh beneath the spots becomes soft and watery, which spreads to the entire Papaya fruit.
- Small, irregular-shaped water-soaked spots on leaves may also be seen and these spots eventually turn brown.
- On the fruits, the symptoms appear only upon ripening and could not be apparent at the time of harvest. Brown sunken spots develop on the Papaya fruit surface, which later on enlarges to form water-soaked lesions. The flesh beneath the affected portion becomes soft and then begins to rot.
- Appropriate protective fungicides applied as a preventive measure are the best for managing anthracnose disease.
- Benomyl or thiobendazole are amongst the important fungicides used to reduce anthracnose of papaya.
- These fungicides are used with or without hot water treatment after fruit harvest. Dipping Papaya fruits in hot water at 48°C for 20 minutes reduces the incidence of the disease after harvesting.
- Planting the papaya tree as a multi-crop that is interspersed with non-hosts of C. gloeosporiodes such as citrus and coffee can help to minimize anthracnose incidence and severity.
- Such planting configurations interfere with splash dispersal of the pathogen spores and thus reduce the population size of the pathogen.
- The affected fruits should be removing and destroyed. The fruits must be harvested as soon as they mature. Then, spaying with Copper Oxychloride (3 g/liter of water) or Carbendazim (1 g/liter of water) or Thiophanate Methyl (1 g/liter of water) at 15 days interval effectively controls the disease. Fruits for exports must be subjected to hot water treatment or fungicidal wax treatment.
Aphids (Aphis gossypii and Myzus persicae)
Symptoms – The young Papaya plants are attacked by the nymphs and adults. Then they suck the cell sap and act as a vector of papaya mosaic virus.
- Spray Nuvacuron (monocrotophos) 36 SL or Malathion 50 EC by 1 ml/liter before the virus attack, as soon as the young insects are seen.
- Uproot and destroy the virus-infected Papaya plants.
Leaf- Blight (Corynespora cassiicola)
Symptoms – The disease causes severe damage to plant leaves. The disease first appears as small, discolored lesions, which are irregularly scattered on the plant leaves. These spots become irregular in shape, then increase in size, and then appear brown to grey. A light yellow zone surrounds the spots and several lesions coalesce to cover large areas of the leaf and in severe infections, the whole leaf dies. A considerable reduction in the crop yield is observed.
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Control – Disease can be mainly controlled by spraying of Dithane M-45 (0.2%) starting from the appearance of the disease symptoms.
Damping-Off (Rhizoctonia solani)
Symptoms – This is a disease of young seedlings and lesions are seen on the stem at or just above soil level. The stem becomes watery and shrinks, followed by the death of the Papaya plant.
Control – Well-drained soil must be used for planting and the crop should not be excessively irrigated. Before sowing the seeds must be treated with the fungal culture of Trichoderma viride (3-4 g/kg of seed) or Captan (3 g/kg of seed) to protect the newly emerging seedlings.
Cause – Fungus (Asperisporium caricae)
Symptoms – Circular water-soaked or brown lesions on older plant leaves; centers of lesions become bleached as they mature; plant leaves curl and turn brown; raised lesions on trunks; sunken circular lesions on fruit. The disease is spread by wind and rain and its emergence is favored by cool weather interspersed with moisture from dew.
- This disease control measures are seldom warranted, apart from general sanitary measures that are removal and destruction of disease crop debris.
- Spraying with foliar protectant fungicides such as dithiocarbamates is very effective.
Cause – Fungus (Mycosphaerella caricae)
- Black sunken rot on young Papaya fruits originating from stem end or contact with a leaf; young fruit dropping from Papaya plant; small, brown sunken lesions with light brown margins on ripening Papaya fruit.
- The fungus enters fruit through wounds.
Management – Protective fungicides similar to those used for a black spot must be applied. Dipping Papaya fruits in hot water at 48°C for 20 minutes reduces the incidence of the disease.
Phytophthora fruit and Stem rot
Cause – Fungus (Phytophthora palmivora)
- Water-soaked lesions on unripe fruit that oozes latex; withering Papaya fruit; water-soaked lesions on leaf scars of the fruit-bearing stem; mature Papaya fruit covered in the white mycelium.
- The fungus survives in soil and enters through wounds in the plant stem. The disease emerges after strong wind damage.
- Use of appropriate protective fungicides, for example, 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 plant roots extend out of the added soil the plant is no longer susceptible to the fungus disease.
- Then, preventive spraying against this disease is done about every 2 weeks in wet locations. In drier locations, the preventive sprays such as mancozeb or copper can be applied every 3 weeks, or less often.
- Once disease appears in a field, the disease can be the main concern due to its ability to spread among plants and destroy fruits rapidly during windy, rainy periods. In that case, curative, systemic metalaxyl fungicides can be used, such as Ridomil Gold Copper.
Bacterial canker and decline
Cause – Bacteria (Erwinia spp)
Symptoms – Main symptoms are angular water-soaked lesions on leaves; lesions coalesce and spread along leaf veins; witling plant leaves, particularly at top of canopy; water-soaked lesion and cankers on the stem; cankers girdle stem and cause plant to collapse; small water-soaked lesions on green Papaya fruit. Bacteria survive in lesions and cankers.
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Management – Copper has been widely proposed as offering a level of control of this disease. Though, its use is controversial. With widespread infections, the recommendation is to remove all affected Papaya plants.
Cause – Disease caused by Rickettsia bacteria transmitted by leafhoppers.
Symptoms – Chlorosis of young leaves; water-soaked spots on petioles and plant stems; petioles rigid, horizontal and shortened; thickened leaf blades that cup downward; internodes shorten and growth stops resulting in a bunchy appearance to the Papaya plant.
- The use of tolerant varieties of papaya is currently the method of control recommended but it has limited application.
- The application of insecticide to reduce the incidence of leafhopper vectors can be beneficial.
Powdery mildew of papaya pests and diseases
The development of powdery mildew in papaya is promoted by high humidity (80-85%) and a temperature range of 24 to 26°C. The powdery mildew disease appears as on the foliage and pods. Infection is first apparent on the leaves as small darkened areas, which later become white powdery spots. These spots enlarge and then cover the entire leaf area. Severely infected leaves can become chlorotic and distorted before falling. Affected fruits are small in size and malformed.
As soon as the powdery mildew disease symptoms are observed dusting Sulphur (30 g/10 liters of water) or spraying Calixin 75 EC (5 ml/10 liters of water) at 15 days interval helps to control the disease
Cercospora black spot of papaya pests and diseases
Cause – Fungus (Cercospora papayae)
Symptoms – Tiny black dots on Papaya fruit which enlarge to about 3mm across; spots are 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 the infestation is severe, leaves can turn yellow and necrotic and drop from the plant. The disease enters orchards from infected papaya leaves in adjacent orchards.
Management – Applications of suitable protective fungicides (mancozeb) at intervals of about 14 to 28 days provide satisfactory control of the disease.
Papaya ring spot virus (PRSV) of apaya pests and diseases
Cause – Virus – transmitted by several aphid species.
Symptoms – Dark green rings on fruit can be sunken and less distinct as the fruit ripens; plant leaves exhibit a bright yellow mosaic pattern and new leaves are small and growth is stunted.
The virus is spread from plant to plant by aphids and the earliest symptoms on papaya are yellowing and vein-clearing of the young leaves. This is followed by a very conspicuous yellow mottling of the plant leaves and sometimes severe blistering and leaf distortion. Dark-green streaks and rings appear in the leafstalks and stems. The disease derives its name from the striking symptoms that develop on Papaya fruit. These contain concentric rings and spots or C-shaped markings, a darker green than the background-green fruit color. Major symptoms persist on the ripe fruit as darker orange-brown rings. Vigour of trees and fruit set is reduced depending on the age of the plant when infected. Fruit quality, particularly flavor, is adversely affected.
Management – Early detection of infected Papaya plants and prompt removal can check the spread of the disease. Aphids can be mainly controlled by the application of Carbofuran (1 kg a.i./ha) in the nursery bed at the time of sowing seeds followed by 2 to 3 foliar sprays of Phosphamidon (0.05%) at an interval of 10 days starting from 15 to 20 days after sowing.
The disease attacks the papaya plants of all age groups but is most serious on young Papaya plants. The aphids are responsible for transmitting the disease and the disease symptoms appear on the top young leaves of the plants. The plant leaves are reduced in size and show blister-like patches of dark-green tissue, alternating with the yellowish-green lamina. The leaf petiole is mainly reduced in length and the top leaves assume an upright position. The infected plants show a marked reduction in plant growth. The fruits borne on disease Papaya plants develop water-soaked lesions with a central solid spot. Such Papaya fruits are elongated and reduced in size.
Control – Good field sanitation such as removal and destruction of affected Papaya plant reduce the spread of the disease.A, losses can be minimized controlling the population of aphid. Application of Carbofuran (1 kg a.i./ha) at the time of sowing seeds followed by 2 to 3 foliar sprays of Phosphamidon (0.05%) at an interval of 10 days starting from 15 to 20 days after sowing effectively checks the population of aphids.
Commonly asked questions about Papaya cultivation, pests, and diseases
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Why do my papayas have spots?
The black spot of papaya is mainly caused by the fungus Asperisporium caricae, previously referred to as Cercospora caricae. This disease is most severe during rainy periods and the disease progresses, small black spots (spores) can be seen on the underside of leaves. If leaves are severely infected, and they turn brown and die.
Why do papayas leave turning yellow?
Papaya lethal yellowing is a disease mainly caused by Papaya lethal yellowing virus (PLYV). The disease symptoms are characterized by progressive leaf yellowing and greenish circular spots on the fruits.
Why is my papaya plant dying?
Papaya trees are tropical plants that produce pear-shaped and melon-like fruit. They can be difficult to grow as they’re sensitive to drought, cold temperatures, high winds, and shade. Insufficient water, disease, or attack by nematodes can all cause Papaya trees to wilt.
How much water does a papaya plant need?
Papayas require plenty of water to grow tasty fruit, but the plants do not tolerate wet feet. To avoid overwatering the papaya, water deeply when the top 1 inch of soil dries.
How much space does a papaya tree need?
Although it is classified as a shrub, papaya trees still have a significant canopy spread of about 5 to 7 feet because the leaves reach up to 3 feet long. As a result of this large foliage, the papaya tree needs between 10 and 20 feet between its trunk and any other plants or structures.
The conclusion of Papaya plant pests and diseases
Well, for better crop yield, and quality of fruit, you must have a minimum knowledge of pests and diseases attacked in papaya crops. The above information may be useful for Growing Dwarf Papaya from Seeds as well.