Black spots on hydrangea leaves may be caused by a number of diseases by fungal, bacterial, and viral pathogens. Common diseases include the Cercospora leaf spot (a fungal disease common in moist conditions) and Anthracnose (a fungal disease which also favors high humidity or precipitation). Remove infected leaves and all plant debris, including fallen leaves, regularly throughout the growing season. Remove any nearby weeds. Prune out any dead/diseased branches, and be sure to disinfect any tools that you use to prune, etc. Provide good air circulation and drainage and avoid overhead watering. Fungicides may help as an early application in spring when symptoms first appear, but would not help this late in the season. Check with your local Cooperative Extension /cooperative-extension-services for advice for the best fungicides to use for your area and purpose. Here’s an article on anthracnose, in case it helps: /pest/anthracnose.
Black spots on hydrangea leaves may be caused by a number of diseases by fungal, bacterial, and viral pathogens. Common diseases include the Cercospora leaf spot (a fungal disease common in moist conditions) and Anthracnose (a fungal disease which also favors high humidity or precipitation). Remove infected leaves and all plant debris, including fallen leaves, regularly throughout the growing season. Remove any nearby weeds. Prune out any dead/diseased branches, and be sure to disinfect any tools that you use to prune, etc. Provide good air circulation and drainage and avoid overhead watering. Fungicides may help as an early application in spring when symptoms first appear, but would not help this late in the season. Check with your local Cooperative Extension /cooperative-extension-services for advice for the best fungicides to use for your area and purpose. Here’s an article on anthracnose, in case it helps: /pest/anthracnose.