|Crop Knowledge Master||Fungi|
|black spot of papaya (Plant Disease Pathogen)|
Wayne Nishijima, Extension Plant Pathologist
Department of Plant Pathology
University of Hawaii at Hilo
HOSTS & DISTRIBUTION
Cercospora black spot of papaya occurs wherever papayas are grown.
Fruit spots start as tiny black dots that eventually enlarge to about 3 mm in diameter. The spots are superficial, slightly raised, a result of the tissue beneath the epidermis becoming corky, and do not develop into a fruit rot. The spots are somewhat obscure on green fruits but become readily visible when the skin color turns yellow as the fruit ripens. Actual damage to fruits is minor except its impact on their appearance and marketability.
Leaf spots are irregularly shaped, grayish-white in color and 1 to 5 mm diameter. Damage to trees is usually negligible but under heavy disease pressure, leaf yellowing, necrosis and defoliation are known to occur.
This disease is most common in poorly maintained, unsprayed papaya fields in wet areas.
Hyaline, multiseptate conidia, 20-75 x 3-5 Ám, are produced on brown, multiseptate, unbranched conidiophores that are 50-200 x 3-6 Ám. Stromata are usually produced on the upper leaf surface.
The primary inoculum source is probably papaya leaves in nearby orchards. In Hawaii, Cercospora black spot occurs when orchards are not sprayed on a regular basis or when protective sprays are not applied as the first fruits are developing.
In a previously unsprayed orchard, harvested papaya fruit continued to be infected with Cercospora black spot for 19 weeks after the start of bi-weekly protective mancozeb sprays, indicating that papaya fruits are susceptible from an early age of about five to six weeks after anthesis.
Protective fungicide sprays at 14-28 days, depending on rainfall, have been shown to be effective in controlling this disease.
Hine, R. B., Holtzmann, O. V., and Raabe, R. D. 1965. Diseases of papayas (Carica papaya L.) in Hawaii. Hawaii Agric. Expt. Stn. Bull. 136, Univ. of Hawaii, 26 pp.
Chupp, C. 1953. A monograph of the genus Cercospora. Published by the author: Ithaca, N.Y.