Cornflower seedlings with blotchy leaves

I have two trays of cornflower seedlings (Centaurea Cyanus - Blue Boy) - one tray is fine while the seedlings in the other tray have blotches on the leaves, the blotches are brown with white centres.

I've been hardening them off for a couple of weeks and now they are permanently outside in their trays (they get a fair amount of direct sunlight). I plan to plant them out soon along with my Cosmos seedlings.

Here's a photo of some of the affected Cornflower seedlings:

http://i59.photobucket.com/albums/g319/Dalek99999/P5150970.jpg

What could be causing this? Is it the type of problem that could spread to my other seedlings (Cornflower and Cosmos)?


Edit: I think it's leaf spot, so best treated organically by removing all of the affected leaves (which I can't do as all of the seedlings would then be leafless!) or spraying with a water mixed with bicarbonate of soda). Or is there a "pet safe" fungicide that I could use? (I have dogs and don't want to take any risks around them by using any "animal unfriendly" chemicals on any plants).

Edit2: In the "unaffected" tray I found one affected leaf which I removed. I notice that the stems on them are a slight purple colour as are some of the leaves on some of the seedlings but in such a way as it looks "natural" (as it's more purple towards the stem of the leaves) so I assume that it's normal colouring. However some of the other seedlings have all green leaves.

 

The bicarb should be pet safe. If they are still in seed trays could you put them out of reach of your dogs?

 

Thanks. Yup I could put them out of reach of the dogs but not in a place that gets sunlight. I'll have a ponder.