Observations on white rot in onions

[bluebellParticipant]

I have been a bit puzzled about how white rot this year. I have sufferd on other parts of the plot in previous years and just pulled out the whole bed of onions, but since they dont keep well ended up throwing some of them away. So this year I planted at the other end of the plot and thought I had got away with it but about 4 weeks ago it struck again. This year I decided to only lift those that had clear signs of white rot. So I have lifted about 60 % of my over wintered onions with white rot, however the other 40% – distribued across most of the bed, including some spring onions I snuck in down the edge of the bed are untouched and growing well.

Theory 1. It is VERY localised and without onions to live on doesnt travel far at all. FInd this unlikley as hoe and rake work would move the soil over these distances.

Theory 2. It requires cool wet weather/soil to spread easily as we have not had prolonged wet spells since I lifted the last one that was showing signs of rot. Our soil is free draining and the top dries out very quickly. I notice also the RHS say that it requires temperatures below 20C 68F, so perhaps it is just the additional warmth?

Theory 3. The ones that have survived were the biggest and healthiest looking to start off with and the spring onions are growing strongly so the white rot only attacks the weakest – or at least has most impact on them first.

Could be any or none of the above but I am fascinated by the fact that it appears to have only effected part of the bed.

I would be interested to hear your experiences.

[charlesModerator]

Most interesting Bluebell, especially about the soil temperature because I have always noticed white rot more in May than in June, and my overwintered onions being more susceptible. I have stopped growing them because they also seem more vulnerable to downy mildew which then spreads to spring-sown onions.

I do very little hoeing and raking and noticed at Lower Farm how the white rot never spread at all, staying very localised in only a few small areas, and I never worked out how it had got there!

As for stronger plants surviving, that is hopeful as one imagines these diseases wiping everything, as with late blight on potato and tomato.

[bluebellParticipant]

Having had a heavy down pour last night I went up the plot this evening and find that some of the spring onions left on the plot are suffering again. Now I am realy puzzled as to the causes.

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