Is there anything when preparing the garden that will prevent Blight?

www.veggiegardener.com/tips-for-preventing-and-treating-tomato-blights/

Put eggshells or Tums down before you plant. A lot of times the blight is caused by lack of calcium.

Early blight, late season blight, tomato blight, potato blight??? There are many reasons and many kinds, most caused by a fungus or a bacteria. Blossom end rot is usually caused by a calcium deficiency, but that is something altogether different. There is a lot of info, but not one thing will treat or help prevent everything.

You can check out these products @ Johnnyseeds.com. I'd first request a catalog from them. I'm an organic gardener so I'm limited to what I can use, they have a nice selection of herbicides, pesticides & fungicides available and show in the catalog what each treats.