Fungus on Zinnias

Fungi may cause a moldy substance that destroys the beauty of a zinnia in bloom.

Zinnias are a popular garden annual known for bringing bright, colorful blooms and texture to the garden. Zinnias are susceptible to several fungal diseases that can cause the development of unsightly, damaged foliage and blossoms.

Types

The most common fungal diseases of the zinnia include fungal leaf spot, powdery mildew and botrytis blight. Fungal leaf spot leads to the development of brown to black patches on the leaves of the zinnia. Powdery mildew causes the plant to become covered in a white, powder-like fungus. Botrytis blight, also known as gray mold, covers plants with a brown to gray mold.

Prevention

Planting zinnias in their preferred locations and spacing them apart to encourage air circulation is one way gardeners can protect their flowers from developing fungi. Zinnias grow best in moist, well-drained soils and full sun.

Considerations

Zinnias belonging to the Z. angustifolia are generally more disease resistant than those in the Z. elegans family, according to the Missouri Botanical Garden. Sanitation is another good practice for zinnia gardeners. Bring a paper bag when checking plants and remove any diseased or damaged plant material.

Treatment

Chemical controls are unlikely to be effective for annual plants, unless plants receive treatment before symptoms develop. Contact the local agricultural extension office for more information on chemical control.

References

• Purdue University: Purdue Plant and Pest Diagnostic Laboratory: Zinnia Diseases
• Cornell University: Botrytis Blight Factsheet
• Missouri Botanical Garden: Kemper Center for Home Gardening: Zinna
• University of Illinois: Hort Answers: Fungal Disease: Powdery Mildew