Botrytis neck rot of onion

Botrytis neck rot of onion is a severe fungal disease caused by the pathogen Botryotinia squamosa (anamorph Botrytis squamosa). It is considered one of the most destructive diseases affecting onion crops worldwide, causing significant economic losses, especially in high-moisture production regions.

The disease symptoms on foliage appear as small, white to tan, slightly depressed spots surrounded by green halos. In the bulb, the disease manifests as tissue softening, starting from the neck area. Under humid conditions, a characteristic gray, fuzzy mycelial growth develops on the neck and bulb surface, which eventually leads to complete decay of the onion bulb.

Development of Botryotinia squamosa is highly dependent on environmental conditions. It thrives in cool, wet weather, with the optimal temperature range for infection being 15–22°C. The fungus persists in the soil as sclerotia or on infected crop debris, serving as a primary inoculum source for subsequent seasons.

The impact of this disease is most profound post-harvest. The pathogen often colonizes the neck of the bulb through wounds caused during harvest or topping. Because infected bulbs may appear healthy at the time of packing, the disease can spread rapidly within storage facilities, resulting in widespread bulb rot and potential total loss of stored batches.

Effective management requires an integrated approach. Farmers are advised to practice long crop rotations and ensure the complete removal of cull piles. Cultural practices such as proper field drainage, timely harvest when tops have naturally fallen, and rapid, thorough curing of bulbs are essential to minimize infection. Fungicide applications during the foliage growth phase can also reduce the initial disease pressure.