What plants are affected?
- Onion smut affects Allium plant species, in particular onions and shallots.
- Spring onions, leeks, garlic and chives are less susceptible to the disease.
What do I look for?
- Onion smut causes distinctive narrow long dark streaks, usually on the cotyledon or the first true leaf, and the leaves become thickened.
- The streaks are evidence of an infection inside the leaf which later bursts through the leaf surface releasing masses of dark-brown powdery spores.
- Onion plants are infected before they emerge from the soil and most infected seedlings die within 3-4 weeks of infection.
- Diseased plants that survive are stunted, distorted and may not produce a bulb.
- Infection is most likely when the temperature is between 12–25°C during germination.
How does the disease survive and spread?
- Onion smut is caused by a fungus that produces many spores as it matures.
- The spores are reported to survive in the soil for many years even when no onions are grown.
- The disease usually spreads through contact with diseased seedlings and soil infested with spores.
What damage can this pest cause?
Onion smut can cause production losses and may result in trade implications for onion growers.
Status in Western Australia
Urocystis cepulae (Schltdl.) Rabenh. 1861 is absent from Western Australia and is a quarantine pest. It is a prohibited organism under section 12 of the Biosecurity and Agriculture Management Act 2007.
Western Australia's pest freedom for onion smut is supported by general and specific surveillance and specific import requirements to prevent its entry. A person who finds or suspects the presence of onion smut must report it to the Department of Primary Industries and Regional Development.
What do I do if I find it?
Early detection and eradication of onion smut will help protect Western Australian onion growers. Please make a report on MyPestGuide or contact the Pest and Disease Information Service (PaDIS) to report this pest.
