|Micrograph of A. niger|
Aspergillus niger var. niger
Black mould (Aspergillus niger) causes rotting in stored onions. It mainly occurs in warmer areas. A. niger survives in the soil and on plant debris. Infection takes place on the necks of onions during the ripening and senescence of the plants.
Clusters of black spores form on and between the outer papery scales.
Because A. niger is transmitted by seeds and sets, a pre-planting treatment may help to reduce infection levels. Irrigation should be stopped not less than 3 weeks before harvest. Damage should be avoided during lifting and loading into stores. High temperatures above 30°C (86°F) for more than 10 days should be avoided. No fungicide is currently used against this disease.