Leaf Spot Diseases on Hydrangeas. Leafy shoots grow from the flower parts. It thrives in warm temperatures over 60 degrees and is most commonly seen in summer. The spores quickly grow on the plant leaves and stems to form a white fuzz that’s also called powdery mildew. If it isn’t a fungal or bacterial problem simply might be mildew which is technically another type of fungus. Cercospora Leaf Spot (also known as Cercospora hydrangea), is typically brown or purple colored spots at the base of the plant. White, cottony fungal growth forms on the lower surface of the leaf. In most cases these leaf spots are indicative of Cercospora leaf spot, a temporary condition caused by the fungus Cercospora hydrangea, which is perhaps the most common disease seen on hydrangeas during the months of July through October.The spots form due to water drops from rain or irrigation that sit on leaves during hot and humid conditions. Leaf Spot. These may become purplish. https://www.ehow.com/list_7427965_white-bugs-hydrangeas.html Learn how to treat the hydrangea leaf spot disease and make your plant beautiful again. Leaf spotting on hydrangea is mostly caused by the fungus Cercospora and affects most of this family of plants. This white fuzzy mold can affect indoor and outdoor plants, especially when growing conditions are warm, damp, and humid. Phytoplasma: Discard infected plants. When the weather conditions are favorable, these areas enlarge until they cover the entire leaf surface. If you notice the bacterial symptoms on the leaves of your hydrangea you can get a bactericide to treat the condition, remove affected leaves and prevent it from spreading. White mold on plants looks like a fuzzy substance that is the result of fungus spores. It appears as brown or purple spots on leaves during wet and humid periods. Fungal Leaf Spots on Hydrangea Leaves. Leaf spot is a very common fungus that affects Hydrangeas. You can try to remove the eggs manually but this is a very hard option and may not be successful. Powdery Mildew This fungus causes white, powdery-looking patches on leaves, eventually resulting in leaf-drop. Powdery mildew is very common in ornamental plants in particular. Plants decline and die. How do i deal with this fungus? Hydrangea Scale: Hydrangea scale is probably one of the most popular pests, they are usually identified by there oval white eggs that attach themselves to the stems of the plant.The pest such the sap from the plant and cause the plants to suffer and not growth as vigorously as they would. In addition to the usual white, powdery fungal growth on the leaf surfaces, yellow or purple leaf blotches might be present. The spots are small that typically measure 1/8 to 1/4 inches in diameter. Virescence: Flowers are green and may be stunted. Powdery mildew causes hydrangeas to develop small tufts of gray or white powdery mildew on the leaves of the plant. 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