The wisteria is a fast-growing vine that produces rich-green foliage with violet-blue blooms. This vigorous grower has a spreading habit that can quickly become invasive, if not controlled. It is tolerant to poor soils and drought conditions and thrives best in full sun. The wisteria is mostly disease resistant, but is susceptible to a few.
Crown gall is a passive bacterial disease that can be quite harmful, if not fatal, to the wisteria. This soil-borne disease enters the wisteria through the wounds of the wisteria's woody areas. The infection causes the infected areas to develop galls on the base and trunk of the tree, as well as on its roots and stems. The girdling galls inhibit the wisteria's ability to pass nutrients and water throughout the plant. As a result, the wisteria becomes starved, experiences dieback and growth stunt, and eventually succumbs to the disease. There is no chemical treatment for crown gall. Wisteria plants can be protected from crown gall by avoiding untimely pruning and injury of the wisteria's woody areas.
Powdery mildew is a mild fungal disease that infects the wisteria's foliage. It attacks the young, newly developing foliage and shoots when humidity levels are high. The infected foliage develops powdery white to greyish-coloured mildew across the leaves' surface that hides the dark, decaying spots on the leaves. Developing leaves grow distorted and are often discoloured. The wisteria's blooms can also be affected by powdery mildew. The infected blooms are often discoloured and distorted, some failing to open and bloom completely. Wisteria plants that remain untreated can experience growth stunt and dieback. Fungicidal treatments are effective methods in controlling and preventing wisteria infections.
Algal Leaf Spot
Algal leaf spot is a fungal disease that spreads during long periods of cool, rainy weather. The causal spores are transported by water onto the wisteria's foliage. The infected foliage develops rough, circular speckles throughout the leaf surface and the margins of the infected leaves become wavy and rippled. The wisteria's twigs develop girdling lesions which block the passage water and nutrients to the leaves. Algal leaf spot is fairly harmless to wisteria plants when treated early. The wisteria's infected areas should be pruned from the plant with sterile shears that are sterilised between each cut. Chemical treatments are effective when applied according to the chemical's directions.
The wisteria's best defence against disease is vigorous growth. To maintain vigorous growth, the wisteria should be planted in a well-drained, fertile area and pruned regularly to remove dead and diseased areas. The wisteria should also be irrigated and fertilised regularly and its planting areas should always be kept free of defoliation and debris.