It occurs when plants are not planted correctly in well-drained soil. There are two forms to worry about. Phytophora Leaf Blight is where the stem will get black and quickly wilt, then die! This should be cut off and destroyed. (Burning is ideal)
The second form is Phytophthora Root Rot occuring within the root zone. This kills the plant quickly and usually shows itself in early spring by way of a wilted (cold-look). Pull the plant from it's location and burn. South Eastern Climates have great difficulty with this specific issue. It might be a good idea to remove the surrounding soil and replace with new soil in extreme or continuous circumstances.