Onion Rust

Onion rust is a disease caused by the Puccinia allii fungus, the same rust fungi that attack roses.

Onion rust (Rasbak) CC BY-SA 3.0

Symptoms of rust

Bright orange pustules grow on affected leaves and seed stalks. They start as white or yellow spots on leaves and stems that turn bright orange, light yellow, or reddish. As the infected tissue dies, these areas transform into black lesions. The fungus can girdle stems, causing them to turn yellow and die, interfering with the plant’s ability to absorb the sun’s energy, resulting in smaller bulbs.


Rust control

To break the cycle of onion rust, rotate all Allium crops every 2 -3 years and discard any infected plant tissue. Other common Allium crops include leeks, scallions, and garlic. Avoid excessive irrigation and remove all dead or diseased plant material.