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What Causes Brown Spots on Hydrangea Leaves?

Updated February 21, 2017

The genus Hydrangea consists of several deciduous shrubs with showy flowers and green leaves. Some diseases, caused by fungi, result in brown spots developing on the leaves of these plants.

Types

According to the Alabama Cooperative Extension System, infected leaves spread the fungus Cercospora hydrangeae, which cause the disease known as Cercospora leaf spot. Another common condition known as Anthracnose occurs when the fungus Colletotrichum gloeosporioldes attacks the plant.

Cercospora Leaf Spot

Cercospora leaf spot begins with small brown or purple spots scattered on the leaves that are nearer to the ground. The spots on the bigleaf hydrangea often turn tan to light grey in the centre and brown or purple in the margins. On oakleaf hydrangea, the spots appear angular and are dark brown to purple throughout.

Anthracnose

According to Alabama Cooperative Extension System, anthracnose attacks bigleaf hydrangea in the landscape and fields, affecting the leaves and the flowers. The brown spots first appear circular or slightly irregular in shape. They then develop alternating dark and lighter rings and become more angular in shape.

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About the Author

Edriaan Koening began writing professionally in 2005, while studying toward her Bachelor of Arts in media and communications at the University of Melbourne. She has since written for several magazines and websites. Koening also holds a Master of Commerce in funds management and accounting from the University of New South Wales.