Spotted Leaves on Geraniums

Fungal Diseases

• Geraniums are susceptible to four fungal diseases that cause spotting on leaf surfaces, geranium rust, gray mold, alternaria and cercospora leaf spot. Geranium rust is a serious fungal disease that causes small, light yellow spots on the lower surfaces of the foliage that expand and turn rust-brown, infecting plants at temperatures between 61 and 70 F. Gray mold causes dark brown spots on the leaves, blossoms and stems of geraniums. As the disease progresses the infected tissue turns brown and dies. Symptoms of Alternaria and Cercospora leaf-spot infections consist of small brown spots with yellow halos surrounding the spots for infection. Severe infections cause defoliation and chlorosis or tissue death. Moisture on plant tissues encourages all four diseases.

Bacterial Diseases

• Bacterial blight is a common and serious disease of geraniums that cause leaf spots as an early symptom. The disease favors warm, humid and wet weather conditions. Symptoms begin as small, water-soaked leaf spots that produce sunken leaf tissue at the infection site. As the disease progresses, the spots enlarge and turn dark in color, infected leaves wilt and premature leaf drop occurs. The disease can spread to the plants stem, which can kill the entire plant.

Maintenance Problems

• Geraniums are susceptible to a disorder known as oedema, which is a water imbalance. Oedema occurs when temperatures are cool, or when the soil is warm and moist, but surrounding weather conditions are cool and moist. Symptoms of oedema consist of rust-brown leaf spots and lesions on leaf surfaces, leaf yellowing and leaf drop.

Management/Control

• Avoid moisture on geranium foliage by watering early in the morning and increase air circulation by pruning large branches to prevent fungal and bacterial diseases. Remove and destroy infected leaves to reduce the severity of fungal and bacterial diseases. Fungicidal application can help control and prevent severe fungal infections of geraniums. There is no chemical control for bacterial leaf spot once infection occurs. Prevent and control oedema by using well-drained potting soil, maintaining plant vigor with proper fertilization and watering and avoid over watering.