Climbing hydrangea is a woody vine that clings and climbs by attaching itself with tiny rootlets to a wall, trellis or other support. The fungus exists in the soil and is moved onto the plant by overhead watering or rain. petiolaris. petiolaris. Ailing hydrangea symptoms do often start at the leaves, even if the affecting disease is root or insect based. Leaf Spot Diseases on Hydrangeas. Leaves Become Black If you do not remove the infected areas in time, the disease will spread quickly to the whole plant. Besides yellowing, there are some other possible leaf problems. Diseases of hydrangea are typically foliar, although root and flowers may also become infected by fungal or viral problems. In most cases, the plant is able to recover with proper care. Climbing hydrangeas. It is common from summer through fall. Leaf spotting on hydrangea is mostly caused by the fungus Cercospora and affects most of this family of plants. Plants are usually infected a month or two before spots appear on the leaves. In this case, you should consider applying a fungicide. The most popular and well-known climbing hydrangea is Hydrangea anomala subsp. Leaves Turn Pale (lighter) Hydrangea leaves may turn pale due to infestation with powdery dew. In early July, it has flat, lacy clusters of fragrant small white flowers that show up well against the glossy green leaves. Also known as Hydrangea anomala ssp. Though slow growing to start with, it is a vigorous climber that can cover outbuildings or brighten up shady house walls.