Onions should be mature and dry when harvested. Onion bulbs need to be carefully handled to minimize bruising and cuts that can allow disease to enter. Onions need a period of curing or drying in order to seal the neck, prevent invasion of diseases and rot and to create a bright, crack-free skin. In temperate regions, curing is usually carried out in storage, but elsewhere, onions are lifted and left to dry in the field.
Excessive nitrogen can result in storage rots, causing yield losses during storage. It can also weaken plant tissues, increasing susceptibility to cold damage. Balanced crop nutrition can help to reduce storage rot by promoting healthy plants.
Later applications of nitrogen are the main cause of increased incidence of thick necks and rot in storage as well as for delayed maturity.
Calcium helps to improve tolerance to diseases. In association with magnesium, onion crops with high levels of calcium in the bulbs show less storage rots.
Calcium nitrate has been proven to be the most effective formulation in ensuring minimal onion rot in storage. It is important that Ca and K are in balance.
Boron and Rotting in Storage
Boron helps to improve calcium uptake and bulb quality. Research shows that a boron supply can reduce onion rotting during storage. This effect is associated with the micronutrient’s role in improving calcium accumulation in the bulb.