Papaya leaf diseases
Brown spot on papaya leaves
Black leaf spot
Brown spot
Cause
The fungus Corynespora cassiicola
Symptoms
Brown spot is a serious foliar disease found in most papaya producing countries. Symptoms of brown spot include light brown circular spots on leaves (Figure 1), long elliptical lesions (several cm in diameter) on leaf petioles and small dark sunken lesions that may develop on fruit. Affected leaves become necrotic under severe disease pressure which causes defoliation of the plant and subsequent fruit blemishes due to sunburn.
Control
Fruit blemishes caused by sunburn and severe fruit infections that can make fruit unmarketable can lead to losses in production of 20–40%. Fortnightly applications of protectant and systemic fungicides are necessary to manage this disease.
Black spot
Cause
The fungus Asperisporium caricae
Symptoms
The initial symptoms of black spot are small circular water-soaked spots (1–3mm diameter) which develop on both leaf surfaces of older leaves and become necrotic and brown to black in colour. Black spore masses form on these lesions on the underside of leaves (Figure 2). Affected leaves curl, become necrotic, brittle and subsequently die under severe disease pressure which results in extensive defoliation. This loss of leaf can lead to fruit blemishes due to sunburn. Lesions on fruit begin as small black dots that can enlarge to 2–6mm in diameter. The tissue beneath these lesions remains firm but the value of harvested fruit with these symptoms is reduced.
Control
Applications of protective and systemic fungicides at 14-day intervals is effective at controlling this disease. The removal of severely affected older leaves prior to spraying these fungicides has been shown to greatly enhance disease control.
Chemical registrations and permits
Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.