A leaf spot disease causes brown or black zonate spots along the leaf margins. When serious, the disease causes severe leaf drop. Insect injury can create entrances for the disease.
Plants grown in high humidity may be attacked by gray mold. This disease is not a problem when plants are grown properly. Use benomyl to control the problem
Anthracnose, also called wither tip, causes spots on the leaves and flowers. Cankers then form on the stem causing wilting of the branch tip.