Powdery mildew causes formation of a white powdery growth or dry, brown, papery leaf spots. Use benomyl to control this problem.
Odema is a physiological condition that may be agrravated by overwatering during periods of high humidity and low light. Light brown corky growths form on the undersides of the leaves and along the stem.
The first symptom of bacterial leaf spot is small, blister-like spots which appear transparent when the infected leaf is held up to strong light. These enlarge and run together causing a blotched appearance. A slimy substance oozes from broken lesions. If The water conducting tissues are invaded, the whole plant may collapse and die. Cut off and destroy lightly infectd tissue and discard heavily infected plants. Reiger elatior begonias are especially susceptible to this disease.
Blotch causes leaves and flower parts to become brown and die. The disease is named for the well marked dead blotches formed on infected tissue.
Several leaf spots attack begonias but most can be controlled by removing the infested leaf and disposing of it.
The stem rot fungus invades the plant crown causing a soft rot which in turn causes the stems to collapse. There is no control.