Wisteria is a woody vine with white or violet blooms known for growing up the sides of buildings or garden structures. But wisteria also is susceptible to fungal diseases that may affect its health. The Missouri Botanical Garden lists wisteria as a high-maintenance plant, because it needs regular pruning and can be invasive.
Sooty canker is a fungal disease that affects wisteria and other woody plants. Powdery mildew, another widespread fungus, is common in wisteria. Fungal leaf spot diseases, which appear in June through August, also attack the vine. Cool, wet weather is favourable for the development of fungal leaf spots.
Sooty canker causes wilting, cankers and dieback in wisteria. The affected plant stems develop brown lesions that hold black fungal spores. Powdery mildew develops as a white, cottony fungal growth on foliage. Leaf spot diseases create tan, black, brown, yellow, grey or purple spots on wisteria leaves. In severe cases, leaves will yellow and drop prematurely.
Powdery mildew and leaf spot are rarely life-threatening for wisteria and usually require no treatment. Sooty canker often kills the area around the canker. Plants under stress are most susceptible to fungal diseases, so keep your plants healthy. Avoid wounding wisteria while pruning, because fungi can enter the plant through injury sites. Remove and destroy infected plant leaves to prevent the spread of disease.