There are as many as 30 species of the elder, or elderberry, tree. Some of the most common selections include the American elder, the Mexican elder and the scarlet elder. These are low-growing trees with a relatively rapid growth rate. They produce rich-green, bushy foliage and are most noted for their blooming bushels that produce small, colourful berries.
Verticillium wilt is an aggressive, soil-borne disease that can live in the soil for many years without a host. Once a host is present, this fungal disease infects the elder through its root system, attacking the tender vascular tissue and cambium. Verticillium wilt restricts the elder's vascular system, inhibiting the flow of nutrients and water throughout the tree. This restricted flow causes the elder to become starved. Its symptoms include wilt, droop, dying branches, growth stunt, premature defoliation and thinning canopies. Initially, only part of the tree will display symptoms while the other areas remain healthy. It may take several seasons for verticillium wilt to kill the elder. However, once the elder begins to display symptoms, it is impossible to save the tree. There is no cure for verticillium wilt. The infected elder should be removed from the area and discarded. No other vegetation should be planted in the spot the elder occupied.
Powdery mildew is a common fungal disease that produces a white to greyish cover of fungal mildew across the surfaces of the elder's foliage. This spore-borne disease is most aggressive during the warm, dry periods of summer but is often transported onto the foliage during the windy, rainy periods of spring. Along with the powdery covering, the infected foliage often becomes distorted and curled, and develops small fungal specks that decay the foliage. Severe powdery mildew infections also cause the foliage to yellow and defoliate prematurely. The elder's powdery mildew is harmless and is an easily treated disease when caught early. A combination of pruning and fungicidal treatments will assist in curing as well as preventing and controlling this disease.
Anthracnose is a leaf spot disease that can be quite damaging to the elder tree. The spores of this fungal disease lie dormant in crevices and defoliated foliage throughout the tree's dormancy period. In the early spring, the spores are swept onto the developing foliage and succulent areas of the elder by wind and rain. The elder's infected foliage develops light-coloured spots that enlarge and darken as the disease progressive. The severely infected foliage decays, wilts and defoliates from the tree. The elder's potential for anthracnose infection is greatly reduced when the tree's area is kept free of debris and defoliation. Anthracnose can be controlled with fungicidal spray applications when the applications are combined with the pruning of the infected areas.
Though the elder requires very little care, its potential to disease is reduced with proper pruning and maintenance. The spores of many infectious diseases lie dormant on dying wood and debris. Reduce the potential for disease by keeping the elder's environment free of debris and defoliation. Prune the elder annually to remove any dead or dying branches or stems. Always remove infected areas immediately with sterile pruning shears that are sterilised after each cut. Thin the interior branches of your vigorously growing elder to increase the light and air throughout the elder, which will also reduce the potential for fungal growth in those areas.