UPDATE ON BASIL BLIGHT
The Basil Blight is still very much with us, heavily attacking the sweet basil types.
The blight is a downy mildew which begins on the bottom of the leaves and appears as a dark gray to black spotted "fuzzy" material. The top of the leaves look yellow at first, then turn tan to brown. Eventually the whole plant collapses. There is still no cure for this disease, so attention should continue to be paid towards prevention.
Basil should be planted in a sunny location with well drained soil, promote good air circulation by increasing plant spacing and planting parallel to the prevailing wind, water early in the day and keep leaves dry, prune (harvest) so as to improve air circulation, and control weeds. Try planting in pots so the crop can be moved around. Another tip: basil should be planted and harvested as early as possible.
One way to approach this situation is to plant less susceptible varieties. It seems the exotic, spice, red, and ornamental basil have some resistance to the blight. So Thai basil, lemon basil, lime basil, cinnamon basil, red leaf, and spice types are all worth a try.