Onion White rot

I have mentioned before about having white rot in my onions and treating the soil with garlic powder.
I still had white rot badly this year (2014) but reading that others seemed to have more success I thought I would try once more. I am not sure where I got the garlic powder last year but when I got some more this year as used for horses it smelt a lot stronger than last years, so I have once more treaeted the soil and will see what happens next year.