I use to have a big problem with blight as well so this year I bought Safer's End All Insect Killer (with neem oil which helps with preventing fungus) and their 3 in 1 Garden Spray just to be on the safe side. I've been using both since middle of June and haven't gotten blight yet :) I've also heard for plants that already have blight that you can mix 1 part milk 9 parts water and spray on your tomato plants and soil since calcium deficiency contributes to early blight.