Did you know that the reason we have this "late blight" is more than likely from the "importation" of tomato plants from the state of Georgia? Who brings them in? Well, surprise, surprise! It is usually the Big Box stores!
This reaffirms why you should try to buy your plant material from a local grower. If the plants are raised locally you can be sure that they will survive and thrive in your garden. And now, another good reason...they don't import diseases we can do so much better without!
I know it's tempting to buy plants from these huge stores. The prices are great...but now all the tomatoes with late blight have to be torn out of the ground and thrown into the garbage...harvest included. Now how much of a bargain was that?
This late blight affects potatoes as well. If just ONE infected potato remains in the ground...it will reinffect any potatoes planted there next year! What a literal pain!
This also graphically shows the benefit of rotating your plants! Move plants around in your vegetable garden year to year, unless they are perennials like rhubarb and asparagus.
Here is a link from Cornell Extension with pictures and more information.