Fungus on Leaves

Fungal diseases such as leaf spot, leaf blister, and leaf rust affect the health and appearance of leaves. Choosing disease-resistant plants helps prevent fungal development on leaves.

Types

Leaf spot diseases such as Septoria affect the leaves of aspens and cottonwoods. Fungal spores infect newly emerging leaves. Wet conditions cause leaf spot fungi to produce cankers on stems of infected trees. Oak leaf blister affects the leaves of red and white oaks, causing blisters on leaves, which become resistant to this fungus as they advance in age. Rust diseases multiply at a rapid pace and cause young trees to lose leaves.

Symptoms

Leaf spot diseases cause lesions on plant leaves. The lesions are either tan and circular, or irregular and brown. The symptoms of oak leaf blister include blisters on upper leaves, which are light green and later turn brown. Leaf rust is characterized by orange lesions on plant leaves that are noticeable in the summer and fall months.

Control

Control fungus by destroying infected leaves, watering in the morning, and spacing trees apart to reduce humidity. Fungicides can prevent or eliminate fungal diseases on plant leaves, but should be applied when symptoms first appear.

References

• Colorado State University Extension: Aspen and Poplar Leaf Spots
• Ohio State University Extension Fact Sheet: Leaf Diseases on Ornamental Trees and Shrubs