Garlic treatment for white rot - update

I use a 3yr rotation on my plot and used the Garlic treatment on the area I grew onions 3yrs ago on which I lost half my onions to white rot .This year after the Garlic treatment on an area 6ft x12ft Ihave lost 1 Garlic blub to white rot  ,not one of the Onions have got White rot .I planted both sets and plants . Both sets and plants small as are most peoples this year.