Cankers, diebacks and wilts are caused by pathogens that infect stems, branches and roots. Because these pathogens affect the water conducting tissues they are considered serious, and in many cases, life threatening. A canker is caused by either a fungal or a bacterial infection. It may appear as a localized lesion or as a discolored/distorted larger area associated with a stem, branch or trunk. Cankers often have discolored areas that become dried out and shriveled so that the outer tissue or bark is wrinkled. In other cases, cankers can appear similar to normal tissue, but show up as flat spots on woody branches or trunks. Cankers commonly enlarge to girdle stems, branches or trunks, killing the water-conducting tissues and causing the death of upper branches or terminal growth (top). This form of dieback can also be caused by root rot fungal pathogens that have invaded the roots or the crown of the plant at the soil line.
Diebacks and declines are often associated with large trees that have been under stress due to adverse environmental conditions such as drought, excess water, and temperature extremes. These stress factors, often combined with poor planting sites, are leading cause of tree mortality. Once dieback and decline are present corrective action may be difficult. Control is best focused on prevention and site improvement. Do not replant the same species into a location where a plant has died of a root problem without making significant site modifications. Ideally plant a different species that is better adapted to the site conditions.
Wilt diseases can be caused by either bacterial or fungal pathogens and result in the interruption of water and nutrient movement to the leaves. These are of the most serious plant disorders and may lead to death within weeks to months. Because pathogens become embedded in the host tissue, they are essentially protected from external control measures. Often there is very little that can be done to manage these problems except to lessen any water stress by improving drainage, or in the case of drought, applying water. Fungal wilt diseases are common in both woody and herbaceous plants. Bacterial wilts are more common for herbaceous plants.