Crop Knowledge Master Fungi

Oidium caricae

powdery mildew(Plant Disease Pathogen)
Hosts Distribution Symptoms Biology Epidemiology Management Reference

Author

Jeri J. Ooka

Extension Plant Pathologist

Department of Plant Pathology, Kaui Branch Office

CTAHR

University of Hawaii

HOSTS

Papayas are the only known host of this fungus.

DISTRIBUTION

Powdery mildew of papaya was initially described in 1898 from Brazil. It has since been recognized in many tropical and subtropical areas of the world including Hawaii, Australia, Bermuda, Florida, Taiwan, India, and New Zealand.

SYMPTOMS

This common disease generally causes little damage or yield loss to bearing trees where lesions are usually found on senescent leaves. However, powdery mildew may severely damage young plants in environments with moderate rainfall and temperatures.

Diffuse mats of white mycelium commonly develop on the lower leaf surface, especially in areas adjacent to the leaf veins, but can occur occasionally on the upper surface of leaves. Initially, infected areas become light green and chlorotic and lesions may be surrounded by a dark green margin. Conidia on the mycelial mat gives it a distinct powdery appearance. Stems, flower pedicels, and fruits as well as leaves can become infected.

Although leaves of all ages are considered susceptible, infection is largely confined to the older leaves approaching senescence. Seedling plants are especially susceptible to attack and may be seriously affected. Defoliation, stem and fruit lesions on young plants may lead to measureable yield losses.

BIOLOGY

Oidium caricae does not have a saprophytic stage and can, therefore, grow and reproduce only on living papaya plants. Seedlings grown in greenhouses are especially susceptible, often killing the apical portions. Disease development appears to be enhanced by low light levels, high humidities, moderate temperatures (18 to 32C), and moderate rainfall (1500 to 2500 mm per year).

Mycelium of O. caricae is hyaline and septate. Haustoria develop in the host's epidermal cells to obtain nourishment for the pathogen. Conidia are hyaline, granular, measure 14-19 x 28-30 m and are borne in chains of three to five or more. The conidial stage is the only form present in Hawaii and other tropical areas. The sexual stage has never been observed.

EPIDEMIOLOGY

Conidia of O. caricae are dispersed by wind.

MANAGEMENT

NON-CHEMICAL CONTROL

Although control measures are generally not needed applications of wettable sulfur, sulfur dust, or lime sulfur have proved helpful in controlling this disease. However, wettable sulfur may be toxic to the plant during hot weather and is not very effective during periods when the disease is severe.

CHEMICAL CONTROL

Fungicides effective in controlling powdery mildew on other crops have generally been effective in controlling papaya powdery mildew. Benomyl, bupirimate, carbendazim, mancozeb, thiophanate-methyl, and triadimefon have demonstrated efficacy in the field.

REFERENCES

Anonymous. 1958. Diseases of the pawpaw. Agr. Gaz. New South Wales 69:534-538.

Chiddawar, P. P. 1955. A powdery mildew on Carica papaya L. Current Sci. 24:239-240.

Chien, H. S., and Wang, H. L. 1984. Seasonal incidence and chemical control of powdery mildew of papaya in Taiwan. J. Agric. Res. of China 33:320-324.

Hine, R. B., Holtzmann, O. V., and Raabe, R. D. 1965. Diseases of papaya (Carica papaya L.) in Hawaii. Hawaii Agric. Exp. Stn. Bull. 136, Univ. of Hawaii, 26 pp.

Obrero, F. P., and Trujillo, E. E. 1968. Control of powdery mildew of papaya. Plant Dis. Rep. 52:814-816.

Raabe, R. D. 1966. Susceptibility of senescent leaves of fruiting papaya plants to powdery mildew. Plant Dis. Rep. 50:519.

Rawal, R. D. 1986. Control of papaya powdery mildew through fungicidal spray. Indian J. Hort. 43:295-298.

Rawal, R. D. 1987. Influences of some weather factors on the development of powdery mildew in papaya. Plant Dis. Res. 2:97-99.

Simmonds, J. H. 1937. Diseases of the papaw. Queensland Agr. J. 48:544-552.

 

 

JANUARY 1993

 

3A-OICAR

Back To:

Crop Master Menu

Knowledge Master Home

Pest Search