How to Control Pests and Diseases in Papaya: Causes, Symptoms, Chemical, and Biological Management

Papayas are commercially important tropical fruits because of their nutritional and medicinal properties. The cultivation of Papaya originated in southern Mexico and Costa Rica. Papayas are popular fruits with high nutritional and medicinal value. Moreover, it bears fruits in less than a year, produces fruits in a high yield per unit area, and starts bearing them earlier than other fruit crops.

The following pests and diseases pose the greatest threat to the papaya industry. Make sure you are familiar with these pests and diseases and monitor your orchard regularly for any suspicious plant pests or fruit symptoms you have not seen before.

How to control pests and diseases in Papaya

Pests in Papaya

Papaya mealybug

The papaya mealybug is a small polyphagous sucking insect with pest status that attacks several genera of host plants, including economically important tropical fruits, vegetables, and ornamentals. Infestation of the mealybug appears as clusters of cotton-like masses on the above-ground portion of plants with long waxy filaments. The immature and adult stages of Papaya mealybug suck the sap of the plant and weaken it.

Damage symptoms

Initially, the affected portion will be chloritic, later changed to brown and dried away.
These bugs excrete honeydew, and as a result infested portion becomes shiny and moist; secondary infection by sooty fungus, Capnodium, occurs in black covering the affected parts.
The papaya mealybug is a polyphagous pest. Symptoms can be observed on ground parts of leaves, stems, and fruits as clusters of cotton-like masses

Biological control

Natural enemies of the papaya mealybug include the generalists, e.g., ladybird beetles, lacewings, and hoverflies.
Several specific parasitoid wasps have controlled infestations in several countries in the Caribbean, South America, and the Pacific.

Chemical control

Insecticidal Soap will work rapidly on heavy infestations. However, this short-lived natural pesticide damages the outer layer of soft-bodied insect pests, causing dehydration and death within hours. Apply 75 ml per gallon of water when insects are present, and repeat every 7-10 days as needed.
As a repellent and antifeedant, neem oil disrupts the growth and development of pest insects. Additionally, it is non-toxic to honey bees and other beneficial insects. Mix 30 ml per gallon of water and spray every 7-14 days, as needed.
Spray anyone of the below listed,

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Chemical compound	Dosage per liter of water
Thiomethaxom	0.5 g
Dimethoate	2 gm
Spirotetramat 11.01% + Imidacloprid 11.01% w/w SC (240 SC)	0.5-1 ml
Flupyradifurone	2 ml

Whitefly

Adult whiteflies have soft bodies and resemble moths. Powdery wax covers the wings, and the body is light yellow. Like a tent, the wings cover the body. There is a slight difference in size between the adult males and females—an adult lives for one to three weeks. Mostly, the females lay their eggs near the veins on the underside of the leaves. The first instar larva moves on the leaf surface to locate a suitable feeding site upon hatching. After inserting its piercing and sucking mouthpart, it begins sucking sap from the phloem.

Damage symptoms

Plant vigor is reduced due to sucking sap by both adults and larvae.
The leaves turn yellow and drop off in severe infestations.
In high populations, they secrete large quantities of honeydew, which promotes the growth of sooty mold on leaf surfaces and reduces photosynthetic efficiency.

Biological control

Use 4-5 traps per acre at yellow sticky traps above 10 cm above the foliage to suppress the population.
Wash off plants with a strong stream of water to wash off whiteflies.
Spray neem seed extract (50g seeds soak and crush and add 1L of water and keep it for 24 hrs, dilute 1:5 and spray).

Chemical control

Spray 200 liters of water with 300 PPM Neem oil early in whitefly outbreaks.
Dissolve 1 kg of Verticillium lecanii in 200 liters of water and spray it on an acre.
Spray Diafenthiuron 50% WP 240 gm per acre by dissolving in 200 liters of water or Acetamiprid 40 gm per acre by dissolving in 200 liters of water if there is a heavy infestation of whiteflies. Alternately spray the pesticides every 10 to 15 days.

Aphid

Aphids are one of the minor pests of Papaya, sucking its juice with their piercing-sucking mouth parts. Having long antennae and legs, these insects are soft-bodied and 20 to 30 mm long. They may be green, yellow, or black, with or without wings. Also, they secrete honeydew, which attracts ants and promotes the growth of sooty mold. It has also been reported that some aphids are vectors of virus diseases in addition to feeding on papaya plants.

Damage symptoms

Infesting tender shoots and under the surface of the leaves.
Curling and crinkling of leaves
Stunted growth
Development of black sooty mold due to the excretion of honeydew
Petioles of heavily infested leaves tend to droop downward.

Biological control

You can largely control the aphid population by keeping the papaya orchard free of weeds.
Release 1st instar larvae of green lacewing bug at 4,000 larvae per acre.
Release predators such as fire ants, robber flies, big-eyed bugs, earwigs, ground beetle, cecidomyiid fly, dragonfly, praying mantis, lacewing, ladybird beetle, spider, etc.
Spraying with tobacco decoction (1 Kg tobacco boiled in 10 l of water for 30 minutes and making up to 30 l + 100 g soap).

Chemical control

Organic control includes insecticidal soaps (1%) and horticultural mineral oils (1%).
If severe attacks occur, spray dimethoate 30 EC 2 ml/lit or methyl demeton 25 EC 2 ml/lit.

Red Spider mite

An adult female is elliptical with a bright crimson anterior side and a dark purplish brown posterior side. On the leaf, mites spin a silken web. After each developmental stage, a quiescent phase follows, and the life cycle is completed within 10-14 days. The eggs are reddish, spherical, and have a small filament. Upon hatching, it will go through two nymphal stages before becoming an adult.

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Damage symptoms

A spider mite’s long, needle-like mouthparts are used to extract the contents of the leaf cells. Consequently, the leaves develop white or yellow speckles due to decreased chlorophyll content.
In severe infestations, leaves will completely desiccate and fall off. Webbing is also produced by the mites on the surface of the leaves when the conditions are extreme.
Under high population densities, the mites use strands of silk to form a ball-like mass, which winds will blow to new leaves or plants in a process known as “ballooning.”

Chemical control

Dust with sulfur. Do not use sulfur if the temperature exceeds 32°C or 30 days after applying the oil spray.
Apply Abamectin at a rate of 10ml in 20 liters of water or 0.5 liters per hectare.
Spraying with Phosphamidon (0.04%) or Methyl Parathion (0.05%) effectively reduces the spider mite population.

Fruit fly

The pest causes damage to the plant and the fruit. Fruit flies can infect Papaya when fruits are allowed to ripen on the tree beyond the recommended harvest stage. The spider mites are small (0.5 mm long) and can only be seen through a magnifying glass. Usually, they are yellow-green or red with or without two dark spots. With the help of its pointed ovipositor, the female punctures the outer wall of mature fruits and inserts eggs in small clusters within its mesocarp.

Damage symptoms

Both young ones and adults suck the sap from the undersurface of leaves resulting in the formation of white or yellow speckles on the leaves.
After hatching, the larvae feed on fruit pulp, and as a result, the infested fruits start to rot
Plants become stunted, and the leaves fall off in severe cases.
Webbing is also produced on the leaf surfaces by the mites. Wind normally spreads mites to new leaves or plants.

Biological control

Spray neem oil or dust with sulfur or other suitable miticides to control the mites
Fruits can be treated with hot vapors of insecticides to kill the papaya fruit fly.
The parasitic wasp Doryctobracon toxotrypanae may also have the potential for fruitfly control

Chemical control

An application like Dimethoate (0.1%) effectively controls the fruit fly.
Traps containing an insecticide like Malathion or deltamethrin combined with a specific bait for males or females are used to control these pests.

Grasshopper

Grasshoppers can decimate your crop. It is because they eat around 50% of their weight daily. So no matter where they are in their life cycle, they will chew away at the stems and leaves of plants in your crop. If left unchecked, this damage can become severe, leaving your entire garden without leaves, unable to grow.

Damage symptoms

Through their sucking and piercing mouthparts, both nymphs and adults suck sap from lower leaf surfaces. Yellowing occurs due to injecting toxic saliva into the plant tissues while sucking the sap.
Yellow spots are left on the leaves when several insects feed on the sap, followed by crinkling, curling, browning, and drying.

Biological control

Parasitoids: Lymaenon empoascae (egg), Anagrus flaveolus, Stethynium triclavatum
Predators: Birds, praying mantis, blister beetle, ground beetle, spider, hoverfly, etc.,

Chemical control

Spray the crop with Malathion at 2 liters per hectare or Endosulphan at 1.25 ltr/ha against insect vectors and grasshoppers.

Reniform nematode

Symptoms

The above-ground symptoms appear as moderate to severe leaf chlorosis and plant stunting. In addition, some wilting may occur during periods of peak transpirational stress on the plant.
Below-ground symptoms are not readily detectable by the untrained observer. However, reniform nematode presence on the roots may be observed with a 10x hand lens.
The small sand-like bodies which remain attached after the root system is carefully washed are egg masses of the nematode.
Fruits produced are smaller than normal and may be slightly bland.

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Chemical control

Carbofuran (2 kg/ha) or Neem cake (1 kg/plant) effectively checks the nematode population.
Apply farm yard manure at 12.5 tons per hectare or neem cake at 500 kg per hectare to withstand and recover from the damage.

Diseases in Papaya

Foot rot of Papaya

Papaya foot rot, caused by a species of Phytophthtora, is a disease characterized by spongy, water-soaked patches on the bark at the soil line. The pathogen inhabits the soil. It can grow and survive on plant resides but attacks living plants in the presence of a favorable host. High relative humidity and rainy condition favor this severe disease development in sick soil.

Disease symptoms

Water-soaked patches near the ground level on the stem characterize it.
As the patches grow, they wrap around the stem, rotting the tissues and turning them dark brown or black. Strong winds can topple such plants and cause them to die.
Only one side of the stem rots in mild disease attacks, and the plants remain stunted.
The fruit, if it forms, is shriveled and malformed. Plants gradually die.

Chemical control and management

Seed treatment with Thiram or Captan 4 g/kg of seed.
Drench with Copper oxychloride 2.5g/lit of water or Bordeaux mixture 1% or Metalaxyl 1g/lit of water.

Anthracnose

Anthracnose is a significant disease worldwide. The soil-borne fungus Colletotrichum gloeosporioides cause it. The fungus survives in seeds or crop residues in the soil. When the conditions are favorable, it spreads to intact, non-wounded, immature green fruits in the field via wind and splashing rain.

The fungus needs the fruits it infests to reach a certain degree of ripening to complete its life cycle. High relative humidity coupled with higher temperatures favors disease development. Wet weather conditions encourage disease development at around 26°C.

Disease symptoms

The disease occurs both in the field and in storage conditions.
It begins as superficial brown skin discoloration on fruits, which develops into circular, slightly sunken spots with a diameter of 1 to 3 cm.
On the margins of the spots, sparse mycelia growth appears as the lesions coalesce.
Salmon pink spores form an encrustation under humid conditions.
Mummification and deformation of fruit are caused by early infection

Chemical control and management

Applying a 1% sodium bicarbonate solution controlled the development of Anthracnose in Papaya, thus being a practical, accessible, and low-cost strategy.
Fungicides containing azoxystrobin, chlorothalonil, or copper sulfate can be sprayed at least three consecutive times with an interval of 10-12 days to lower the risk of infection. Seed treatment with these compounds can also be envisaged.

Powdery mildew

The fungus Oidium caricae-papayae causes the disease. The fungus survives and reproduces on papaya plants only. The spores are dispersed from plant to plant and between fields by wind. All growth stages can be affected, but older leaves are more susceptible. Low light levels promote the development of the disease and the severity of the symptoms, a high degree of humidity, moderate temperatures (18 to 32°C), and rainfall ranging from 1500 to 2500 mm per year.

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Disease symptoms

Patches of whitish powder growth are found on the undersurface of the disease leaves.
Yellow or pale green blotches characterize infection sites on upper surfaces, usually near veins, surrounded by typically colored tissue.
Occasionally, the fungus may attack the stem of young seedlings when grown under reduced light conditions.
Spots enlarge and cover the entire leaf surface. Chlorotic and distorted leaves may result from severe infection. In addition, the affected fruits are small and malformed.
Fungus grows on the undersurface of the leaves withdrawing nutrients from the cell of the leaf surface by a specialized absorbing structure known as haustoria.

Chemical control and management

Spray using baking powder, neem extracts, white mineral oil, and soap solution are alternatives for control.
Dust with Sulphur 80%w/w at a rate of 30g/10 liters of water
Spray with Triadimefon at a rate of 40gm/20ltrs water at 10-14 day intervals.

Papaya ring spot disease

A plant virus known as Papaya ringspot virus – type P (PRSV-P) causes papaya ringspot disease. PRSV-P belongs to the Potyvirus family. Aphids transmit PRSV, and the virus is acquired and transmitted in a non-persistent manner by its vector in short periods that are measured in seconds to a minute.

Disease symptoms

Infected plants initially display chlorosis on their youngest leaves, followed by vein clearing, rugosity, and prominent mottling.
Malformation and reduction of the lamina, which may become highly filiform
Characteristically elongated dark green streaks develop on the petiole and upper half of the stems; infected fruits show circular concentric rings that cause up to 56-60 % yield loss.

Chemical control and management

The most effective treatment was applying neem oil 1% + Dimethoate 1.05% with the least disease incidence (6.66%) and 41.66%, respectively, at 60 and 150 DAP.
Apply any one of the below listed active ingredients containing fungicides,
Flonicamid
Imidacloprid
Pymetrozine
Acetamiprid
Chlorpyrifos

Papaya leaf curl disease

Papaya leaf curl disease is caused by begomovirus, Papaya leaf curl virus (PaLCV). The virus is transmitted primarily by the whitefly Bemisia tabaci. Viruses are spread in a non-persistent manner from plant to plant. The transmission occurs within a few seconds while the virus remains in the vector. The disease is spread through infected seedlings or seeds and grafting material.

Disease symptoms

Curling, crinkling, distortion of leaves, reduction of leaf lamina, rolling of leaf margins inward and downward, thickening of veins.
Leaves become leathery, brittle, and distorted, and plants become stunted. Affected plants do not produce flowers and fruits.
Sometimes all the leaves at the top of the plant are affected by these symptoms. Defoliation occurs in the advanced stages of the disease, and the plant’s growth is arrested.

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Chemical control and management

Viral infections cannot be treated chemically. It is possible, however, to reduce the infection’s severity if the whiteflies population is kept in check. Dimethoate or Metasystox can be applied to the soil when sowing, and 4-5 foliar sprays applied every ten days can effectively control whiteflies.
Removal and destruction of the affected plants is the only control measure to reduce the spread of the disease.

Conclusion

As perishable fruits, papayas should not be damaged or blemished. However, fungal contamination can occur from these sources. Consequently, the fruits would decay quickly, reducing their market value. So keep an eye on the above-discussed pests and disease and their control methods to limit the losses.

How to Control Pests and Diseases in Papaya: Causes, Symptoms, Chemical, and Biological Management

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