Botryosphaeria canker is a widespread and destructive fungal disease that impacts a broad spectrum of woody plants. It is caused by several species of fungi belonging to the Botryosphaeriaceae family. These fungi behave as opportunistic pathogens, primarily attacking plants already weakened or stressed. The disease can lead to significant branch dieback and overall decline in plant health.
Symptoms and Visual Identification
Early recognition of Botryosphaeria canker symptoms is important. A primary indicator is the formation of cankers, which appear as sunken, discolored areas on the bark of trunks, stems, and branches. These lesions can vary in size, ranging from small spots to extensive areas that completely encircle or girdle an entire branch, interrupting the flow of water and nutrients.
Cutting into an infected branch often reveals wood discoloration beneath the bark. This underlying wood may appear dark brown or black, in contrast to the healthy, lighter wood. Another common symptom is sudden wilting and death of branches or twigs, often referred to as “flagging,” where leaves turn brown but remain attached to the stem. On some host plants, gummosis, or sap oozing, may be observed from cankered areas.
Susceptible Plants and Contributing Factors
Botryosphaeria canker affects a wide array of woody plants due to the Botryosphaeriaceae family’s broad host range. This includes many common fruit trees such as apple, cherry, and grape, as well as landscape trees like oak, maple, dogwood, and pine. Numerous shrubs, including rhododendron, azalea, and holly, are also commonly affected.
The fungi can exist latently within healthy plant tissues. Disease development occurs when the plant experiences stress, which compromises its natural defenses. Common contributing factors include prolonged periods of drought, excessive heat stress, and sunscald. Poor soil conditions, nutrient deficiencies, and physical injuries from pruning, hail, or insect damage also predispose plants to infection.
Management and Prevention Techniques
Effective management of Botryosphaeria canker focuses on both controlling existing infections and preventing future occurrences. Pruning infected branches is a primary control measure. Cut well below the visible canker into healthy wood, typically several inches beyond any discoloration. Sanitize tools by soaking them in a 10% bleach solution or using 70% alcohol between cuts.
Reducing plant stress is the most effective long-term prevention strategy. Providing consistent and adequate watering, especially during dry periods, helps maintain plant vigor. Applying a layer of organic mulch around the plant’s base can help retain soil moisture and regulate root zone temperatures. Avoiding unnecessary wounding from lawn mowers or trimmers, and ensuring proper plant nutrition through soil testing and amendments, also enhance plant resilience.
Fungicides are generally not effective for treating existing cankers because the fungus penetrates deep into the wood. While some fungicides may offer limited preventative value when applied to fresh pruning wounds or during high-risk periods, cultural practices remain the most impactful approach for managing this disease.