Papaya Diseases
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Papaya Ring Spot on Fruit
Fig. 1
Papaya ring spot on fruit

Sunken Lesions with Pinkish Spore Masses on Fruits
Fig. 12 
Sunken lesions with pinkish spore masses on fruits

Papaya Mildew on Fruit
Fig. 17 
Powdery mildew on fruit

Corynespora leaf spot
Fig. 24 
Corynespora leaf spot
 Phytophthora Blight on Fruit
Fig. 25 
Phytophthora blight on fruit

Phytophthora Blight on Fruit Column
Fig. 26 
Phytophthora blight
on fruit column

Phytophthora Blight on Stem (basal stem rot)
Fig. 27 
Phytophthora blight
on stem (basal rot)

Phytophthora blight of papaya caused by Phytophthora palmivora: Stem rot
Fig. 32 
Phytophthora blight of papaya caused by Phytophthora palmivora: Stem rot

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The principal diseases affecting papaya include papaya ringspot virus, anthracnose (Colletotrichum gloeosporioides), powdery mildew (Oidium caricae), leaf spot (Corynespora cassiicola), and blight (Phytophthora spp.). Other diseases that intermittently affect papaya production are papaya droopy necrosis virus and yellow strap leaf (the latter resulting from a toxin produced by Aspergillus wentii, which is absorbed from the soil through the roots).



Papaya ringspot virus

Caused by the Papaya Ringspot Virus (PRSV) (Fig.1)

Papaya ringspot is a potyvirus that is the most important disease of the crop in Florida, even to the point of limiting the potential for commercial production. Earliest signs of papaya ringspot virus infection appear as yellowing and vein-clearing of younger leaves. A prominent yellow mottling of the leaves follows. One or more lobes of infected foliage may become blistered, roughened, or narrow, with blades curving upwards from the midrib.

Mottled Stem Mosaic & 'Green Islands' Ringspot on Fruit Ringspot on fruit
Fig. 2 Fig. 3 Fig. 4 Fig. 5
Foliar Mosaic Shoestring Streaking on Petiole
Fig. 6 Fig. 7 Fig. 8
Vein Clearing Streaking on petiole Affected Field
Fig. 9 Fig. 10   Fig. 11

Fig. 2. Mottled stem
Fig. 3. Mosaic & 'Green Islands'
Fig. 4,5. Ringspot on fruit
Fig. 6.  Foliarmosaic
Fig. 7. Shoestring
Fig. 8. Streaking on petiole
Fig. 9. Vein clearing
Fig. 10. Petiole streaking & water soaking
Fig. 11 Affected field

Further Reading
Papaya Ringspot Virus (P-strain) from the Crop Knowledge Master Hawaii University Extension ext. link



Anthracnose
Caused by Colletotrichum gloeosporioides (Fig.12)

The fungus attacks primarily the fruit of papaya, with mature fruit being more susceptible. Petioles and leaves may be infected, but this is thought to be important only as a source of the fungus for further fruit infection. The disease signs begin as small, water-soaked spots on ripening fruit. As the spots develop, they become sunken, turn brown or black, and may enlarge to a few inches. The fungus may produce a pink mass of spores in the middle of the older spots. The pathogen grows into the fruit, resulting in softening of the fruit and an off flavor. Growers practice a prophylactic program for this disease.

Sunken Lesions with Pinkish Spore Masses on Fruits Sunken Lesions with Pinkish Spore Masses on Fruits Sunken Lesions with Pinkish Spore Masses on Fruits Complete Decay of fruit with Spore Masses
Fig. 13 Fig. 14 Fig. 15 Fig. 16

Fig. 13,14,15. Sunken lesions with pinkish spore masses on fruits
Fig. 16. Complete decay of fruit with spore masses



Powdery Mildew
Caused by Oidium caricae (Fig.17) This fungus is easily recognized by the presence of a white, superficial growth on the leaf surface. The disease begins as tiny, light yellow spots on the lower leaf surface. As the spots enlarge, a white powdery growth (fungal hyphae and spores) appear. Pale yellow spots then appear on the upper leaf surface at the infection position. In advanced stages, white fungal growth will develop on the upper leaf surface. Powdery mildew is not a severe problem but some leaf drop can occur.

Mildew on Fruit Papaya Mildew on Fruit Papaya Mildew on Fruit
Fig. 18 Fig. 19 Fig. 20
Powdery Mildew on Leaf Powdery Mildew on Leaf Powdery Mildew on Leaf
Fig. 21 Fig. 22 Fig. 23

Fig. 18,19,20. Powdery mildew on fruit
Fig. 21,22,23. Powdery mildew on leaf

Further Reading
Powdery Mildew (Plant Pathogen) from the Crop Knowledge Master Hawaii University Extension ext. link



Leaf Spot

Caused by Corynespora cassiicola (Fig. 24)

This is a disease primarily of the leaf blade but will occasionally occur on petioles and male flower stalks. It has not been observed on fruit or stems. 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 0.2–0.4 in. (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.



Phytophthora Blight

Caused by Phytophthora palmivora, pseudofungus (Fig. 25,26,27,32)

This fungus is capable of causing damping-off, root rot, stem rot, stem girdling, and fruit rot. Complete loss has been seen in some Miami-Dade fields. Cool, wet environmental conditions with high soil moisture favor disease development. Damping-off occurs in very young plants or in the field shortly after transplanting and is characterized by rapid wilting and plant death. Spots on the stems of established plants begin as water-soaked lesions, especially at fruit and branch scars. These areas can enlarge and girdle the plant, resulting in wilt and death of the plant top. Root infection can be severe and rapid. The first indication of major root infection often is rapid browning and wilting of the plants, followed by total collapse within days. The root infection also has a foul odor. 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 evidence that the fungus is present. Diseased fruit then become covered with a characteristic mass of whitish fungal growth. Fruit eventually shrivel and fall to the ground, where they serve as an important source of inoculum for root rot. 1

Phytophthora Blight on Fruit Phytophthora Blight on Fruit Phytophthora Blight on Fruit Phytophthora Blight on Fruit
Fig. 28 Fig. 29 Fig. 30 Fig. 31
Phytophthora Blight Stem Cankers Latex Phytophthora blight of papaya caused by Phytophthora palmivora: Basal stem rot and collapse Phytophthora Blight Destroyed Field
Fig. 33 Fig. 34 Fig. 35 

Fig. 34. Toppled plant
Fig. 33. Incipient stem cankers latex
Fig. 34. Phytophthora blight of papaya caused by Phytophthora palmivora: Basal stem rot and collapse
Fig. 35. Destroyed field

Further Reading
Phytophthora Blight from the University of Hawaii Extension pdf 7 pages
Phytophthora Disease Caused by the Giant African Snail



Further Reading
Florida Crop/Pest Management Profile: Papaya from the University of Florida pdf 7 pages

Bibliography

1 Mossler, and Crane, Jonathan. "Florida Crop/Pest Management Profile: Papaya." edis.ifas.ufl.edu. This document is CIR 1402, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date, September 2002. Original authors included O. Norman Nesheim, professor, Food Science and Human Nutrition Department. Revised Nov. 2009. Reviewed July 2013. Web. 18 Feb. 2017.

Photographs

Fig. 1,2,3,4,5,6,7,8,9,10,11 Nelson, Scot C. Ringspot (Papaya Ringspot Virus, PRSV). N. d. hawaiiplantdisease.net. Under (CC BY-SA 2.0). Web. 2 Apr. 2014.
Fig. 12,13,14,15,16 Nelson, Scot C. Anthracnose Caused by Colletotrichum gloeosporioides. N. d. hawaiiplantdisease.net. Under (CC BY-SA 2.0). Web. 7 Apr. 2014.
Fig. 17,18,19,20,21,22,23,25,26,27,28,29,30,31,32,33,34,35 Nelson, Scot C. Phytophthora blight (Phytophthora palmivora, pseudofungus). N. d. hawaiiplantdisease.net. Under (CC BY-SA 2.0). Web. 8 Apr. 2014.
Fig. 24 Brock, Jason. Corynespora leaf spot on cotton. 2010. University of Georgia. bugwood.org. Under (CC BY-NC 3.0 US). Web. 7 Apr. 2014.
Corynespora leaf spot
 
Published Feb. 2014 LR. Last update 18 Feb. 2017 LR
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