The hydrangea shrub is a popular sight in many southern landscapes. Its full white, blue, pink or purple blooms and deep green foliage are synonymous with this deciduous shrub. The plant is native to Japan and has several varieties. It is also susceptible to several fungal diseases that affect hydrangea grown in a greenhouse as well as in a landscape.
Most Common Diseases
There are six diseases that may affect the hydrangea: Powdery mildew, Cercospora Leaf Spot, Anthracnose, Botrytis Blight, Mushroom Root Rot and Phytophthora Root Rot, according to the University of Alabama Extension office.
Powdery mildew is easily detected by the presence of small, white circular patches on the leaves. The patches have a feathery-like edge to their appearance. As the disease progresses, all leaves may become covered with the white fungus causing the plant to become discoloured and stunted. Powdery mildew can be treated with a foliar fungicide spray. For maximum results, both sides of the plant's leaves should be sprayed.
Cercospora Leaf Spot
Cercospora leaf spot first develops as small, round purple or brown dots on the plant's leaves, located at the base. Heavily infested leaves become discoloured, turning yellow-green and often fall to the ground. Cercospora leaf spot can also be treated with a fungicide spray at the earliest detection of the disease.
Anthracnose is easily detected by the presence of large, circular spots that can attack the plant's blooms and leaves. Anthracnose most commonly affects greenhouse-grown hydrangea, rarely those grown in the home landscape. The best defence is to remove diseased branches and blooms to prevent the fungus from spreading.
Botrytis Blight affects the flower buds, especially the petals, causing a brown, withered mass. Good cultural control practice (removing diseased branches to further prevent spreading the disease) is the best remedy for Botrytis Blight, but it may also be controlled with a fungicide spray.
Mushroom Root Rot
Mushroom Root Rot affects hydrangea grown in a landscape setting where it is evident by the sudden wilting of foliage. It is best treated with good cultural control and fungicidal spray, if needed.
Phytophthora Root Rot
Pytophthora Root Rot affects those that are grown in greenhouses in a container and is evident by the sudden wilting of foliage. If Phytophtora Root rot progresses, leaves may shed or turn yellow. Try controlling the fungal disease with good cultural control, but if it does not respond to this treatment, use a fungicidal spray.