Some Common Diseases of Papaya
Diseases are the most important limiting production problems of papaya. Although the plant is classified botanically as perennial, virus diseases have reduced the effective crop life to 1-2 years.

Virus Diseases

I - Papaya Ring spot

Papaya ring spot, caused by papaya ring spot virus, is the most important disease of the crop, severely limiting the potential for commercial production. Earliest symptoms appear as yellowing and vein-clearing of younger leaves. A prominent yellow mottling of the leaves follows. One or more lobes of infected leaves may become severely distorted and narrow

The disease has been named because of the striking symptoms that appear on fruit. These consist of circles and C-shaped markings that are darker green than the background fruit color later, these markings may become gray and crusty in texture.

Infected plants exhibit growth reduction. There is reduced fruit set, and quality, especially flavor, is adversely affected.

Papaya rings pot virus can be transmitted mechanically and by grafting. However, it is thought that aphid transmission is the most important mechanism for disease spread in the field.

Control

Until recently, little could be done to effectively control this disease. Attempts to reduce disease levels by applying aphicides.

2 - Papaya Apical Necrosis

Papaya apical necrosis is a relatively new virus problem in Florida. It is caused by a newly discovered virus (papaya apical necrosis virus or droopy necrosis virus) that is quite different from papaya ring spot virus.

Symptoms

The first symptoms are drooping and downward cupping of leaves in the upper part of the plant. Blades of the youngest leaves are pale yellow, sharply cupped downward, and do not expand properly. Petioles are short and stiff, and stem internodes become very short.

The disease usually increases in severity in the winter. Leaves often develop marginal necrosis, and those near the stem tip begin to drop. The tip of the stem usually dies. The disease progresses down the stem until the entire plant is dead.


Fungal Diseases

1- ANTHRACNOSE

The causal organism Colletotrichum gloeosporiodes

Symptoms

The disease an important fungus disease that primarily affects papaya fruit. The disease symptoms begin as small water-soaked spots on ripening fruit. As the spots develop, they become sunken, turn brown or black, and may enlarge to 2-5 cm in diameter. The fungus may produce a pink mass of spores in the middle of these older spots. The pathogen can grow into the fruit, resulting in softening of the tissue and an off flavor of the pulp

Infection of older petioles may occur, but this is thought to be important only as a source of the fungus for further fruit infection.

Control
                   At the begging of fruit set Use

          COBOX               250g/100L.W
OR     AMISATR           45cm/100L.W

2- POWDERY MILDEW

The causal organism Oidium caricae

The disease is easily recognized by the presence of a white, superficial growth on leaf surfaces. The disease begins as tiny, light yellow spots on the lower surface of leaves. As the spots enlarge, a white, powdery growth, the actual body and spores of the fungus, appears on lower leaf surfaces. At this time pale yellow areas appear on the upper leaf surface at the infection sites. In advanced stages, white fungal growth will develop on the upper leaf surface of leaf lesions

          The great masses of spores produced on infected leaves are readily spread by wind currents to healthy plants. Year-round production of papaya permits uninterrupted reproduction of the fungus and continuous presence of the disease in an active state.

Control

                  AMISATR                    45cm/100L.W
OR             BELLIS                        50g/100/L.W                
OR             KUMULLUS-s             250g/100L.W


3- PHYTOPHTHORA BLIGHT

The causal organism Phytophthora parasitica

The fungus causes a wide range of damage, including damping-off, root rot; stem rot and girdling, and fruit rot.

Symptoms

Damping-off is the rapid wilting and death of very young plants. This occurs in production houses and in the field shortly after transplanting.

Spots on the stems of established plants begin as water-soaked lesions, especially at fruit and branch scars. These areas can enlarge and even girdle the tree, resulting in wilt and death of the top of the plant.

Root infection can be very severe. Unfortunately, the first indication of major root infection often is rapid browning and wilting of the trees, followed by total collapse of the plants within days.

Fruit infection is the most obvious aspect of the disease and potentially very important economically, because of the possibility of carry-over to the market. Water-soaked spots are again the first evidence of infection. Diseased fruit then become covered with a characteristic mass of whitish fungal growth. Fruits eventually shrivel and fall to the ground, where they serve as an important source of Phytophthora inoculums for root infection.

Phytophthora blight is a wet weather disease. The spores of the fungus are spread by wind and splashing rain. The spores must have free water to germinate, producing large numbers of smaller swimming spores that invade healthy tissue.


4- CORYNESPORA LEAF SPOT

The causal organism Corynespora cassiicola

Symptoms

Older leaves are most likely to be affected. Symptoms are first evident as small, yellow areas. Fully developed spots have a small 0.1 in. (2 mm) brown center, with a prominent, yellow halo. 4-8 mm when leaf spots are examined closely, one may observe faint, concentric rings. C. cassiicola forms spores on both upper and lower leaf surfaces, but masses of spores are most evident on the latter. Examination of lower leaf surfaces with a hand lens for a dark growth of the fungus body and spores is important for diagnosis of this disease.

Heavy infection results in premature defoliation with losses in yield and possibly fruit quality.

Control

                   COBOX               250g/100L.W
OR             AMISATR           45cm/100L.W


5- YELLOW STRAP LEAF

The causal organism Aspergillis wentii

Symptoms

The first symptom of yellow strap leaf is a yellowing of new leaves, especially along the leaf margins. Leaf blades become narrow and, in severe cases, appear strap-like. Tips of leaf lobes are hooked downward or laterally toward the midrib, and are thicker than normal. Petioles and internodes become very short, often giving the trees a bushy appearance. Female flowers do not develop normally and do not set fruit. Male flowers are stunted toward the stem tip and produce no pollen.

Plants with yellow strap leaf are usually in more or less circular "hot spots" in the field, with the most severely affected plants in the center of the affected areas.

Yellow strap leaf is a serious problem in hot, rainy weather. Papayas may show dramatic recovery during the dry season, but symptoms can recur when conditions become favorable.


6- ROOT KNOT

The causal organism Meloidogyne SP.

Symptoms

The larvae of these nematodes can travel short distances in soil, finding and attacking papaya roots, usually near the tips. When female larvae feed near the water-conducting core of the roots, the plant cells increase in number and size until readily visible swellings, called galls or "knots" are formed. To confirm a diagnosis, one can cut into the galls and observe pearly looking, pear-shaped female nematodes embedded in the tissue.

Leaves of papayas that are affected by root knot nematodes appear pale green or slightly yellow and are generally unthrifty. They may be more sensitive than normal to water stress. Fruits are smaller than normal and more likely to have an off-flavor.

Control
         
To control root knot nematode problems, avoid heavily infested land if possible. It is recommended that papayas grown in land likely to be infested, for example, "old" vegetable land, should be set in raised, mulched beds that have been fumigated

Papaya Insect & pests

1- Fruit fly

The causal organism Toxotrypana curvicauda

The insect is the principal insect pest of papaya

Description

Adult: Commonly mistaken for a vespid wasp due to its size, form, coloration, and behavior, the papaya fruit fly is predominantly yellow marked with black. The female has a very long, slender abdomen with a greatly elongated curved ovipositor which exceeds the length of its body (length: body, 8.5 to 12.5 mm; ovipositor, 9 to 14 mm). The male fly resembles the female with a hairy, but less markedly banded stalked abdomen and without the ovipositor

Egg : Long, slender, yellow egg with a long cylindrical stalk. The average length is approximately 2.5 mm, and the largest diameter is 0.2 mm.


Symptoms

The primary diagnostic characters for papaya fruit fly larvae involve the large anterior spiracles.

Fruit infected with papaya fruit fly larva will turn yellow and drop from the tree prematurely. Damage levels in Florida fluctuate between 2 and 30% of fruits infested during the spring-summer season.

Control
ACTELLIC         150cm/100L.W