Buddleia davidii, also known as butterfly bush, is a perennial shrub that produces fragrant purple flowers that are known for attracting butterflies. This plant prefers full sun and well-drained soil but is relatively tolerate of most conditions. In addition, butterfly bush is well known because it is relatively disease and pest free. However, there are some diseases that can attack Buddleia davidii.
Fungal Leaf Spots
Fine Gardening, an online gardening web site states that butterfly bush is susceptible to fungal leaf spots. Fungal leaf spot is a common fungal disease that affects many garden and landscaping plants. According to the Texas AgriLife Extension's "Earth-Wise Guide to Fungal Leaf Spot," fungal leaf spot is caused when wet conditions persist for long periods of time. Infestation is especially likely when water is allowed to sit around the base of the plant or on the leaves in moist and warm weather. The disease is characterized by small lesions that have dry brown or black centers. Fungal leaf spot causes leaves to yellow and drop. Since the disease spreads, always remove any fallen leaves from the plant. In addition, plants should be spaced out to provide air circulation. Gardeners should also avoid watering the plant from above, which allows water to get on leaves.
Fine Gardening also mentions dieback as another disease associated with Buddleia davidii. Dieback can occur over a series of growing seasons and is not often identified until the disease has progressed significantly. The University of Illinois Extension Service's Integrated Pest Management said that dieback, also referred to as decline, refers to the progressive death and decline of shrubs and trees starting at the tips of the plant. UIES recommends using a bleach solution, one part bleach to 10 parts water, to treat an infected plant.
Tomato Ringspot Virus
According to The New York Botanical Garden, butterfly bush is relatively free from disease. "The Invasive Butterfly Bush" by Nina Tallent-Halsell and Michael Watt in the September 2009 "Botanical Review," cited a study conducted by P.L.Hughes and S.W. Scott in 2003, asserting that some varieties of Buddleia davidii are susceptible to ringspot. The virus is caused by infected nematodes which eat at the root of the plant causing the plant to contract the virus. Tomato Ringspot can be identified by a decline in overall health of the plant as well as yellowish and wilting foliage. Because this disease is spread through nematodes, controlling the disease means controlling nematode population in your soil.