Wow, that's a toughie. Your garden needs a roof to keep the rain off. Removing bottom leaves is good, as is anything else that gets more air circulation: thinning out the branches to let air in, planting further apart, etc. Also something on the ground (garden cloth, wood chips, etc) to keep soil from splashing.
I haven't heard of seedlings being harmed by copper products, but someone with more experience should chime in on that. Have you considered Serenade? I think it covers leaves with good microorganisms so the baddies can't get in.
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