Onion sets problem

Hi all my onion sets are doing really well but when i looked at one of the bulbs iv noticed a white mould\powder on it,i looked at all the others and there the same any ideas!!

sounds like white rot nothing you can do only lift and dispose of the crop DON@T COMPOST it use the ones that have a good size but they will not store
trouble with white rot it stays in the soil for eight years I have half of my plot affected
try and grow on another part of the plot.

Is it fluffy white mould? or flat and mildewy looking?
Makes a lot of difference...