White rot: identify, prevent, control

Updated October 2026

Worst in cool, moist soil between about 10 and 20 degrees, so from late autumn to spring across southern Australia, especially Victoria and Tasmania.

White rot is a soil borne fungus that attacks only plants in the onion family, including onions, garlic, spring onions, leeks, shallots and chives. Industry sources describe it as the most destructive fungal disease of onions and spring onions in Australia. Its tiny black resting bodies, called sclerotia, can survive in soil for 20 years or more without a host, so the best defence is never to let it into your garden.

Stromatinia cepivora (syn. Sclerotium cepivorum)

How to identify it

• The oldest leaves yellow and die back from the tips, and the plant stops growing, often in a small patch that widens along the row.
• Affected plants wobble or pull out of the ground with almost no effort, because the roots have rotted away.
• The base of the bulb or clove is covered in a fluffy white mould that looks like cotton wool.
• Within the white mould you can see tiny round black specks the size of a poppy seed, which are the sclerotia that carry the disease over in soil.
• The bulb becomes soft and watery and rots completely, and garlic cloves turn grey and collapse inside the papery skin.

What it is often confused with

When and where it is worst

White rot can occur in any Australian garden where onions and garlic have been grown, but it is most active in cool, moist soil. Victoria and Tasmania have the biggest problems in commercial crops, and Tasmanian researchers have studied it closely because it threatens the onion industry there. Home gardeners in Melbourne, Hobart, Canberra, Adelaide and the tablelands of NSW are most likely to meet it, usually from May to October while garlic and onions are growing.

The sclerotia lie dormant until they sense the roots of an onion family plant, then germinate and infect. They are spread in soil on tools, boots and wheelbarrows, in infected garlic cloves and onion sets, and in compost made from infected plants. Warm, dry soil above about 24 degrees slows the disease, which is why it often seems to stop in late spring.

Plants it affects

These plants in our library list it as a problem to watch for.

How to prevent it

• Buy garlic and onion sets from a reputable supplier, and never plant cloves from supermarket garlic or from a crop that had rotted bulbs.
• Rotate onion family crops so that onions, garlic, leeks, shallots and spring onions do not return to a bed for at least four years, although this will not clear a heavy infestation.
• Do not move soil, potted plants or compost from a garden known to have white rot into your own beds.
• Clean soil off tools, boots and wheelbarrow tyres before moving from an infected bed to a clean one.
• If you share plants with friends, give them seed or clean bulbs rather than divisions of chives or spring onions with soil on the roots.

Organic control, step by step

• Dig out affected plants carefully with the soil around the roots, bag them and put them in the rubbish bin, never in the compost or green waste.
• Mark the infected bed and stop growing onion family crops there, then grow them in pots of fresh potting mix or in a raised bed filled with new soil instead.
• Solarise small infected beds in the hottest part of summer by watering them and covering them with clear plastic for six to eight weeks, which kills some of the sclerotia near the surface.
• Grow other crops such as brassicas, lettuce, beans and tomatoes in the infected bed, as they are not affected by white rot.

Conventional control

• No fungicide is registered for home garden use against white rot in Australia. Commercial onion growers use tebuconazole applied at planting, but this is not a home garden use and does not clean the soil.
• Because there is no chemical fix, hygiene, clean planting material and keeping onion family crops out of infected beds are the only reliable control.
• If you use any garden fungicide on onion family crops, always read the label, check that your crop is listed, and keep to the withholding period.

Frequently asked questions

Related problems

Sources: Tasmanian Institute of Agriculture (University of Tasmania), Modelling onion white rot in Tasmania; AUSVEG VIC, Onion white rot; UC IPM, Onion and garlic white rot. Identification and control follow these sources. Always read the product label before use.