There is no chemical cure for bacterial leaf spot. Make sure and destroy infected plants and plant parts this fall. Another common disease of geranium is a fungal disease known as botrytis leaf spot or botrytis blossom blight. It is caused by Botrytis cinerea . Botrytis is favored under cool, moist conditions or where plants are watered frequently.
Leaves develop zonate, brown leaf lesions which develop a grayish brown mass of fungal spores.
The lower leaves will yellow and rot. Flowers may also become infected. They show discolored petals which wilt and fall. Remove affected leaves and flowers. Fungicide sprays, when environmental conditions are favorable, will help reduce levels of this disease.