There is a better solution...
Unfortunately the A4A search engine is going doolally and only finds the most recent post - I needed to open a fresh A4A window to get sensible results for "onion rot" - and I can't get back to it without opening yet another window - so I had to cut&paste what I was looking for from March 2015:
BarriedaleNick: Yes..
There is a thread somewhere about this - I think I may have even started it! AH found it..
http://www.allotments4all.co.uk/smf/index.php/topic,78156.msg792062.html#msg792062I tried a small patch last year with great success but empirically it isn't significant as I need to replicate it this year.
I used garlic powder and liquidised onion and watered into my test bed. Previously the test bed had produced onions with white rot but not all were affected so I think it was a decent enough test. I didn't get any rot at all - not a smidge. However several fellow growers didn't get as much rot as previous so maybe it was a dry year or something else was affecting the amount of rot. So not at all conclusive but well worth a shot.
Small: I was delighted with my first year trial of mashed up garlic watered in, barely a sign of rot and a really good crop of onions, shallots and leeks. Did the same again for last year, and lost at least half the crop, had to pull the rest early and freeze rather than store the usual way......I don't think I did anything differently, but I couldn't bear risking the disappointment again so I'm afraid for me it's Tesco from now on. Good luck if you decide to give it a try, let us know how you go on.
Check out BarriedaleNick's link.
Cheers.