[Gandan57]

Went to the plot today, first time in three days, and to my dismay, my autumn and spring planted sets are all showing signs of mildew on the leaves.

I cannot understand how this has occurred this early with the dry weather we`ve had.

Advice please on how I can salvage something.

[Trillium]

Here's something that might help:
http://www.which.co.uk/documents/pdf/onion-downy-mildew-153656.pdf

Normally mildew comes in wet weather, but I find that often mildew shows up when the plants are too dry. Once mildew shows up, you really can't get rid of it, but you can slow it with regular, deep watering. You don't want to overdo watering onions as this affects their storage ability, but you want enough water there to keep the plants healthy.