Help advice about my onions and garlic please!

Some of my onions have started to wilt and die. Pulling them up I have found a fluffy white mould with black bits on it on the bulb which is soft. Looking it up it looks like white onion rot My garlic has just started doing the same. Does anyone have any advice about what I should do? We've grown both & leeks over the past 4 years with no problems. Any ideas where it may have come from? Would it have been dormant in the soil? We grew onions in the same bed in 2009 with no rot. I'm a bit concerned as we have a lot of leeks just planted out

It sounds like bad news angelcakes- have a look at a recent thread http://chat.allotment-garden.org/index.php?topic=78845.0
As Learner says you would be wise to avoid planting any of the alium family in that bed for some time. It persists for ages once it is in the soil but checkout the link in the other thread where it is suggested that by watering in garlic powder it is possible to "trick" spores into germinating only to then find no alium plant to host them so they die.

 I am in the same boat as you having found my garlic and onions are infected. I have lifted them both, sorted out the "good" garlic for storage and plan on using the infected stuff soon. Some just needs chucking. WARNING - dont put the affected stuff into your compost.
Good luck!