Many hybrid pansies have a high tolerance for cold, can be frozen quite solid and the plants will not die. You may notice a purple cast to the pansy leaves. This is a sign of stress and can be a result of cold temperatures. It is relatively easy to keep pansies free from damage caused by diseases and pests. Here a re a few of the more common problems that may be encountered.
Root rot -The first sign of root rot is yellow leaves.
The plant then becomes stunted or dwarfed in stature. Leaf spot -Leaves will develop spots of red, brown or yellow. Mildew -Plants show white powdery deposits on leaf and stem surfaces. Growing plants where they will receive adequate air circulation may prevent mildew. The above diseases are best controlled by prevention.