Posted: 27/04/2014 at 13:01
That's mostly all true, Christopher, though their advice to spray after you find early symptoms of Early Blight is crook. The only effective spray technique is preventive - before the spores arrive. Once leaves are infected, there's no killing the spores apart from removing infected leaves and destroying them.
Late Blight is a lot, lot less common in domestic gardens. Early Blight is probably the most common domestic fungal problem, along with Septoria Leaf Spot.
My point was only that covering the plants won't protect from infection. Won't even reduce the chances. While damp foliage can be an incubator, the spores will still infect dry foliage. I see it every season. I get zilch rain in summer, have very low humidity, and still end up with Early Blight.