Sclerotium cepivorum 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.