Tan to occasionally reddish discoloration of berries that are starting to rot. White cultivar fruits will turn tan or brown, while fruits of purple cultivars will turn purple or pink. Fruit flies and fruit fly larvae are generally present in large numbers. Initial symptoms of sour rot are similar to those of green and blue moulds. Fungus degrades the rind, segment walls and juice vesicles into a slimy, watery mass. At high relative humudity, the lesions may be covered with yeasty, sometimes wrinkled layer of white or cream colored mycelium.
Damage is caused by a variety of naturally-occurring fungi. Invasion by pathogens usually occurs at the point of injury to the berries, which could be caused by mechanical growth or cracks, injuries from insect or bird feeding, or lesions as a result of powdery mildew infections. Tight clusters and thin skins result in more susceptible cultivars. Favorable conditions such as warm moist conditions and sugar accumulation in berries encourage the fruit fly to lay hundreds of eggs. Pathogen occurs commonly in soils and is wind borne or splash borne to surfaces of fruit within the tree canopy. As fruits mature, they become more susceptible to sour rot infection. Disease development depends on high humidity and temperature above 10°C , with the optimum being 25-30°C, sour odour associated with the advanced stages of sour rot attract flies (drosophila spp.), which can disseminate the fungus and cause other injured fruit to become infected. Sou rot spores in the soil can accumulate in recirculating water in dips and drenches.
Use antagonistic yeasts of Peroxidase (POD) and Superoxide dimutase (SOD) to control the development of sour rot.
Always consider an integrated approach with preventive measures together with biological treatments if available. Utilize general antimicrobial such as hydrogen peroxide, and solutions of potassium metabisulfite. Antimicrobial treatments are usually more effective when combined with insecticide treatments against Drosophilia flies. Apply guazatine fungicide within 24 hours of harvest.