[jarigo]

What is the cause of white rot in onions and what can I do in future if any thing.

[peapod]

Its a fungal infection in the soil, and they recommend that you dont grow any alliums for the next approximately 20 years   

Its effectively impossible to get rid of while growing alliums as it remains dormant until it can 'breed' again on your onions/garlic or shallots.  It then dies off until the next lot are planted.

Sorry to be the bearer of bad news.

[jarigo]

Many thanks for reply Peapod don't think I will be growing onions in 20 years time.

[peapod]

Well...its an option anyway 

[mumofstig]

It seems that garlic spray will help with white rot and some commercial growers have started to use it. It was discussed recently on this thread
http://chat.allotment-garden.org/index.php?topic=81442.msg911289#msg911289

[peapod]

I remember Jekka advocating garlic spray as a prevention against slugs and snails this year too.  

It would be great if it did work, garlic is well known for a lot of benefits as we all know.  Wouldnt it be interesting if after all the chemical solutions that didnt work this actually would?  Makes you think about many old fashioned remedies and their effectiveness.