White rot or not?

[Sweet savory]

I harvested my dozen onions grown from seed in August and have happily used them since. But the last one’s root came off easily to reveal a white cotton wool like patch and the inside was pretty rotten. This is the only one to have been affected by what I assume is possibly white rot?? after a bit of picture research and if so it seems very localised.
Have grown garlic and shallot sets from reputable supplier and leeks (from seed) for the past 3 years on this plot with no problem and had not planted alliums before on the bit I grew the onions on.
Just surprised if it is onion rot that it hasn’t affected the whole crop.
Will sterilise all tools used on the plot - as soon as it stops raining - and my gardening shoes etc Have carefully disposed of the offending item also.
Any other thoughts as to what to do would be welcome
Ssvy

[Snoop Puss]

Are you able to post a photo of the onion concerned? Might it have gone mouldy in storage rather than before you picked it?

[Sweet savory]

Apologies for the delay.

[Mark_Riga]

I would assume it was white rot and keep any eye on future crops. In my experience, I think, if it has been dormant a long time on a plot, it strikes later in the year so if you grew onions in same place next year, you might see it in late June/July.
In future, I would plant onions/garlic at least 6" apart in rows 1' apart so there is less chance, if one is affected, that it spreads to its neighbours. Keep an eye on the crop from late June onwards looking for yellowing leaves or check the firmness of the roots by giving a gentle pull. If I do find any, I remove a spadeful of the immediate soil carefully and dispose of it. I don't have bonfires but that might be a good place to put it.

[Mark_Riga]

Also, thinking about it, if it seemed OK when you harvested it and the roots were fine then, it probably isn't white rot. You usually know when you pull up an onion as the roots are generally rotted away and the onion comes out very easily. If it is white rot, it probably didn't have time to reproduce in the soil so should be OK.

[Snoop Puss]

Have a look at the pictures here of the black sclerotia typical of white rot. When you harvested the onion, did you see evidence of sclerotia? There's also some advice on how to treat your soil if it is white rot:

https://www.growveg.co.uk/guides/how...ion-white-rot/

[Thelma Sanders]

I agree with Mark, I'm sure you would have noticed white fluff at the bottom of the bulb, and that you would have noticed when you took it up that their was no root resistance.
I always found the bulbs just came away from the soil with the slightest touch, noticeably different from the healthy bulbs.
Just make sure you always rotate your onion planting in future

[Sweet savory]

Thanks for all your thoughts. I didn’t notice any of the black sclerotia shown in the pics at harvest time and don’t remember any of the crop being less resistant than the others at harvest. It was primarily the white fluff that got me wondering and the fact that the root just dropped off when I picked it up.
I do a 4 year rotation but can vary the onion patch within this as well from now on and will be vigilant for any symptoms in future.

[Scarlet]

I haven't been able to grow any onions or garlic for several years due to white rot.

I think you would have had more of an issue if you did...but it's worth following Marks advice regardless just Incase.

Make sure you get your garlic from a good supplier