Common Hydrangea Pests and Diseases: Identification, Prevention, and Treatment

17.07.2024 - 13:21 / finegardening.com

As one of the most popular flowering shrubs for the modern landscape, it is no surprise that we are now seeing more evidence of various diseases and insect damage on Hydrangea sp. It was once a plant rarely afflicted by pests, but extensive use in the landscape has created more opportunities for common pest problems.

Two common leaf spot diseases impact hydrangeas in similar ways but with diverse sources. In both cases, the plants benefit from removing diseased leaves from the area. Pruning also opens the plant and provides good air circulation, which can aid in keeping these problems under control. Diseased or infested sections of your plants should always be bagged and placed in the trash or burned if allowed, never composted. All pruning tools should be cleaned thoroughly and disinfected between plants.

Yellowing leaves with circular spots, typically brown or purple, at the base of the plant can usually be attributed to one of two pathogens, both fungal diseases. Fungal leaf spots (Cercospora species and Phyllosticta hydrangea) can be prevented by keeping the leaves dry when watering. However, hot, humid weather and heavy rains cannot be prevented. Wet weather patterns create the perfect conditions for spreading these pathogens. If your plants become infected, treat them with a commercial fungicide containing Chlorothalonil, or use organic options. Compost tea, garlic oil, liquid kelp, and hydrogen peroxide are recommended as well as Neem Oil and sprays that contain Bacillus subtilis. With that said, this disease is cosmetic and will not kill the plant.

A disease common to oakleaf hydrangea (Hydrangea quercifolia) is bacterial leaf spot (Xanthomonas campestris). Entering the plant through wounds and natural openings