Oh, crap. Late Blight Fungus Threatens Tomato Crop in Northeast and Mid-Atlantic.
“…the outbreak spread in part from the hundreds of thousands of tomato plants bought by home gardeners at Wal-Mart, Lowe’s, Home Depot and Kmart stores starting in April.” We started a bunch of ours from seed but two of the ones I’ve got in containers are organics from Home Depot.
Here’s info on identification and treatment.