Hydrangea Tree Diseases


Growing bold hydrangeas in your yard provides brilliant color in late summer and early fall. Most known for their ability to produce either pink or blue blooms, depending on the soil pH, these delightful shrubs have waxy evergreen leaves making them ideal for landscaping even when not in bloom. Hydrangeas are relatively easy to grow and maintain, but are susceptible to some diseases.


Hydrangeas are susceptible to leaf spot, powdery mildew, bud blight and root rot.


Leaf spot appears first at the base of the plant and progresses upward and outward overtaking all branches. Leaf spots are ¼ to ½ inch in diameter and may have a tan or brown center with a dark circle around it. It is most prevalent in late summer or early fall. Powdery mildew appears as spots or circles of powdery white substance with irregular edges. Areas may appear purple or yellow. Untreated, hydrangea foliage and stems may become completely covered with white powdery mildew. Bud blight appears as a gray mold that affects buds and blooms. In cool, damp weather, it may appear overnight and progress rapidly. Root rot presents with wilting and yellowing of leaves that may appear on one side of the plant and progress to the entire plant. Crown rot becomes obvious as the disease continues.


Bud blight infects buds and blooms, causing them to quickly lose color and turn brown. Dropped leaves may exhibit leaf spots. Leaf spot causes yellowing of foliage and leaf drop but rarely kills the plant. Reduced flowering and unsightly plants usually result from a leaf spot infection. Plants infected with powdery mildew produce fewer blooms that are reduced in size and lack the brilliant hues of healthy plants. Root rot affects the entire plant and often kills the plant entirely. Fungicides will not cure the root rot once it occurs.


Bud blight is best treated by prevention, but if it is caught early, application of fungicide and a clearing away of diseased plant debris may halt its progress. Leaf spot requires a fungicide. Treat plants infected with powdery mildew with a fungicide. There are many available at your local garden store. Always check that it is labeled for the treatment of powdery mildew and apply following the manufacturer's directions. Root rot requires destroying the plant as fungicides are ineffective in combating the disease once the plant is infected.


The best defense against bud blight is proper maintenance. Remove and destroy dead or decaying plant debris. Application of fungicides prior to symptoms prevents bud blight. Begin application before plants set blooms. Leaf spot prevention consists of providing adequate nitrogen to encourage vigorous growth, removing plant debris from the soil and surface watering. Spores in the soil that are splashed on the foliage during rain or watering transmit the fungus that causes leaf spot. Powdery mildew prevention consists of providing adequate ventilation and spacing plants farther apart to allow air circulation. Reduce relative humidity and remove any leaves or other plant debris from the soil regularly. Prevent root rot by keeping the area around your hydrangea free of decaying plant debris, providing adequate water--both over and under watering contribute to root rot--and applying fungicide to the soil prior to symptoms.

Keywords: hydrangea diseases, root rot, bud blight

About this Author

Nannette Richford is an avid gardener, teacher and nature enthusiast with more than four years' experience in online writing. Richford holds a Bachelor of Science in secondary education from the University of Maine Orono and certifications in teaching 7-12 English, K-8 General Elementary and Birth to age 5.