Help us achieve our goals:
make a donation »
Join the RHS today and support our charity
Free personalised gardening advice
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Make a donation
I have forgotten my password
Keep me signed in
Register for free to receive our newsletters, add comments to blogs/articles and to save content.
See what events are on near you and browse your bookmarked pages.
White rot is a serious fungal disease of onions, garlic and leeks causing wilting and yellowing foliage. It may persist in the soil for many years.
White rot is a serious disease of plants of the allium family, especially bulb onions, garlic and leeks, caused by the soil-borne fungus Stromatinia cepivora (syn. Sclerotium cepivorum), which can persist in the soil for many years. Look for symptoms from mid-summer until early autumn.
You may see the following symptoms:
Stromatinia cepivora is effectively impossible to eliminate once it has been introduced and the long survival period makes crop rotation impractical. It is therefore extremely important to avoid introduction to previously clean sites. It is transported in contaminated soil, for example on tools or on muddy footwear. Take particular care in areas where cross contamination can occur easily, for example on allotments.
There are no chemical treatments against this disease or for soil sterilisation available to UK gardeners.
As mentioned, the sclerotia are stimulated to germinate by volatile compounds emitted by onions. Therefore the possibility exists of using the compounds as a chemical soil treatment to trick the sclerotia to germinate and then die because of lack of suitable plants to infect. This has been under discussion for many years, but has not translated into the availability of any products on the UK amateur market.
Stromatinia cepivora is an unusual fungus in that it does not produce any spores of importance to the normal life cycle. It exists in the soil as round black resting structures (sclerotia) about 0.5mm (1/32in) diameter, which remain dormant so long as no members of the onion family are grown. Sclerotia can detect certain volatile chemicals unique to alliums and when these are sensed the sclerotia germinate, producing fungal growth which invades the roots directly. Fresh sclerotia are then formed on the rotting bulbs and recontaminate the soil.
Sclerotia can remain in the soil for at least 15 years, though they will not always live this long. They can only germinate once and the fungus will then die out if it can not infect. Both sclerotial germination and fungal growth are inhibited above 20ºC (68ºF), so in the UK the problem is more severe in cool, wet summers; in warmer climates the disease is only a problem over the winter months.
Allium leaf minerLeek mothLeek rustOnion downy mildewOnion flyOnion neck rotOnions and shallotsSclerotinia diseases
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
Register for the site or sign in to share your experiences on this topic and seek advice from our community of gardeners.
Aid Renegade on 30/05/2015
Could hot composting be used to kill the fungi and create fungi free soil to grow onions etc in? I've heard hot compostng (layers of greens and browns) is good for killing off weed seeds.
We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.
Join the RHS today and get 12 months for the price of 9