What causes Onion Rot?

What causes Onion Rot?


Onion bulb rot may be caused by bacterial or fungal pathogens.

Accurate diagnosis of bulb rot (bacterial, fungal, or other) is important to select an effective management strategy.

For example, fungicides are not effective in controlling bulb rot caused by bacteria.

bulbrotbacteria

Bulb rot caused by bacteria

InTheOnionBulb

Bulb rot caused by fungus (Botrytis neck rot)

Bacterial bulb rot may be caused by dozens of different types of bacteria.

It is generally not possible to determine the type of bacteria that caused the rot based on bulb rot symptoms. Samples would have to be sent to a diagnostic lab.

To learn how to identify bulb rot caused by bacterial pathogens, and to distinguish it from bulb rot caused by other factors including fungal pathogens and abiotic factors (such as bruising), check out this video:

English video (4 min)

Spanish video (4 min)

In the field, bacterial diseases cause chlorosis, water-soaking, and collapse of the inner leaves of the plant.

field1
field2
field3

In severe cases, all of the leaves collapse and die.

field4
field5

Not all plants with foliar symptoms of bacterial disease result in bulb rot.

Sometimes bulb rot results from onion plants without foliar symptoms of bacterial disease.

To learn how to identify foliar symptoms of bacterial diseases in onion, and to distinguish it from other “look-a-likes”, check out this video:

English video (4 min)

Resources:
Flip Cards for Onion Bacterial Disease Diagnosis

flipcard1
flipcard2