Onion basal rot

[charlesModerator]

I had this question from Colin Hammond, posted it here in case others are suffering from it:

“Hi please could you offer any advice on soil treatment after removing a crop of onions that have basal rot. All the info I have read suggest to leave the bed onion free for at least 4 years is there any way of shortening this time and how did the basal rot fungus get into the soil ?
I have been rotating my crops around 3 beds.”

This rotting from soil upwards is becoming more common and I think that infected sets are to blame. Colin did not say if he grew from sets or seed. I have noticed it occasionally on set-grown onions and its a good idea not to plant any sets showing signs of mould or rotting, they should be bright and firm.

Once in the soil, I have not found it spreads wildly and have not re-suffered it after a 3 year gap, but I only had a small amount of onions infected.

[DevParticipant]

This sounds like the dreaded onion White Rot. I have this on my allotment – but strangely very patchy. Some spring onions have had it, but others in the same row haven’t. Similarly, I have raised onions (Kelsae) from seed and some have it and some not. Same with shallots. Some leeks were affected last year. It shows as a white fungal growth at the base of the bulbs leading to rotting.
I understand from the Hessayan book that it could be 8 years before it clears – sorry to be the bearer of bad tidings if this is what it is.

[charlesModerator]

Hello Dev, I beg to differ as it sounds like basal rot which is not the same as white rot. Yes they are two separate and major problems. What you describe is definitely white rot and is fairly common on allotments where alliums have been grown for a long time, I hope you can cope with it. 4-8 years is average resting time in my experience.

[Author]

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