Onion rust is a disease caused by the Puccinia allii fungus, the same rust fungi that attack roses.
The rust fungi gets its name because of the bright orange pustules that form on affected leaves and seed stalks. This fungi begins as white or yellow spots on leaves and stems that then turn bright orange, light yellow, or reddish. These areas turn into black lesions as tissue is destroyed. As the fungus grows, it can girdle stems, causing them to turn yellow and die. This interferes with the plant’s ability to absorb the sun’s energy, resulting in smaller bulbs.
How to control rust
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.
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