Anthracnose of Papaya and Mango
· Mango · Papaya
Anthracnose can manifest itself on leaves and petioles, but it is mainly a fruit disease. Symptoms on leaves show as gray to brown spots with darker margins and a yellow surrounding halo. The spots later enlarge and coalesce to form sizable necrotic areas. Small, light-colored spots appear first on the skin of fruits. As they mature, the spots grow considerably in size (up to 5 cm) and become round, dark brown lesions, often with a water-soaked or raised appearance. Pinkish to orange specks grow within the lesions in a concentric manner. Smaller, reddish-brown, sunken spots (up to 2 cm), referred to as "chocolate spots", are also visible. Fruits tend to fall off prematurely. These symptoms might develop after harvest, particularly if the fruits are refrigerated.
Anthracnose is an important disease worldwide. It is caused by the soil-borne fungus Colletotrichum gloeosporioides. The fungus survives in seeds or crop residues in the soil. When the conditions are favorable, it is spread to intact, non-wounded, immature green fruits in the field via wind and splashing rain. Alternative hosts of the pathogen include mango, banana and avocado, among others. Moderate temperatures (the optimum is between 18 and 28°C), very high humidity (97% or more) and low pH (5.8 to 6.5) favor the development of the disease in the field. Dry weather, high solar radiation or temperature extremes, inhibit its growth. The fungus needs the fruits it infests to reach a certain degree of ripening to complete its life cycle.
Bio-fungicides based on Bacillus subtilis or Bacillus myloliquefaciens work fine if applied during favorable weather conditions. Hot water treatment of seeds or fruits (48°C for 20 minutes) can kill any fungal residue and prevent further spreading of the disease in the field or during transport.
Always consider an integrated approach with preventive measures together with biological treatments if available. Fungicides containing azoxystrobin, chlorothalonil or copper sulfate can be sprayed regularly to lower the risk of infection. Seed treatment with these compounds can also be envisaged. Finally, post-harvest fungicides together with a food-grade wax can be applied to reduce the incidence in fruits bound to be shipped to overseas markets.
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