What diseases attack hydrangeas?
Powdery mildew (Erysiphe polygoni) can be a problem during times when day temperatures are warm, nights are cool and high humidity (Spring & Fall). Good air circulation will help prevent the onset. While disfiguring the foliage, it is not fatal. There are various fungal diseases that can spot both the flowers and the leaves. The most likely culprits are fungal leaf spot (Cercospora hydrangeae) in late summer & fall if the season is rainy or anthracnose (Colletrichum gloeosporioides) on H. macrophylla during hot, wet weather. Neither are normally fatal but cleaning away the diseased leaves after they drop for winter will help keep the problem from recurring the following year. Root rot (Phytophthora nicotiana) is common on oakleaf hydrangeas grown in a container. It is caused by excessive moisture in the growing mix. The same problem can occur on oakleafs planted in a constantly wet spot in the garden. Good information about these diseases is on Auburn University’s web site at: http://w
