If You have an organic garden, you need to read this article:
"How to Fight Late Blight on Tomatoes Organically
The disease that caused the Irish potato famine is raging across America. Learn how to protect your organic garden.

It's a major challenge, all right, but after losing all the tomatoes in New York, we're trying to see if at least one of the Maine tomato patches can fight off late blight (Phytopthera infestans), one of the most devastating vegetable diseases. It's the one that led to the Irish potato famine and it's just as deadly almost two centuries later.
P. infestans is always around, but it came early this year, and more ferociously than ever before. Farmers and home gardeners from Maine to South Carolina -- and quite a way west -- have already lost their crops to what has turned out to be the most widespread outbreak in U.S. history.
If you see any signs of late blight, experts advise destroying all infected plants at once, to stop the spread of spores. And if you live in an area where there are gardens or farms that have not yet been hit that is the advice to take; late blight is highly contagious. But if everyone else already has it and yours is the garden that's hanging in, you might as well join us in employing:"
