How to Identify Common Hydrangea Fungal Diseases
Fungal diseases are quite common on Hydrangeas, but are rarely severe enough to kill the plant. All the fungal diseases listed below can be controlled and prevented through certain measures. Avoid watering overhead as wet leaves create the perfect environment for many fungal diseases. Thinning out crowded plants is also an important preventative measure. Once the fungus is identified, prune back any infected leaves and branches and discard in the trash. Remove mulch and debris from the base of the plant and destroy, replacing with new mulch. Spores can live in the mulch cover.
Gray mold, also called Botrytis, is a fungal disease that affects many different garden plants. During cool and moist periods, it spreads rapidly, creating soft, gray spots on leaves and turning flowers or buds brown. Over time, the mold covers larger areas of the plant. Although gray mold won’t kill your hydrangea, it causes leaves and flowers to drop prematurely.
Powdery Mildew This fungus causes white, powdery-looking patches on leaves, eventually resulting in leaf-drop. It thrives in warm temperatures over 60 degrees and is most commonly seen in summer.
Leaf spot is a very common fungus that affects Hydrangeas. It appears as brown or purple spots on leaves during wet and humid periods.
Rust Hydrangeas may also be infected with rust, a fungal disease that causes red or copper-colored spots on the undersides of leaves. In severe infections, the upper part of the leaf may also turn yellow or brown and drop prematurely. Apply neem oil regularly in spring to prevent the development of rust.