Call me Mr Sceptical, but I don't see how spreading something on the ground can deter airborne fungal spores (the only way blight can reach your spuds) from landing and germinating on leaves. From what I read about hydrogen peroxide, there's little evidence of its efficacy apropos of blight and at what concentrations. And as soon as it leaves your sprayer, it's turning into water and oxygen... I think I'll stick to choosing early varieties that evade the worst of midsummer attacks, and remove the tops as soon as I see blight infection. Look hard enough and you'll find myth-busting articles on cornmeal on the web.