Verticillium wilt infections will discolor the wood beneath the bark. Severity of symptom development is influenced by host susceptibility and environmental conditions. Trees under drought, nutrient, or salt stress are more extensively invaded by this pathogen. An infected tree may die in a single season or linger on for many seasons, with branch after branch dying and being invaded by decay or canker fungi. Cause Verticillium wilt is caused by the soil-borne fungus, Verticillium alboatrum .
Infection occurs through the root system.
The fungus is an excellent soil inhabitant, and produces resting structures that can survive in soil for many years. The fungi that grow from these structures can directly penetrate roots of susceptible host plants. Growth within the host occurs within the water-conducting tissues, resulting in blockage of water movement from the roots to the foliage. The tree responds to infection by plugging some water conducting vessels with gums and other materials which further restricts water flow. Management Do not replant susceptible species where a specimen was killed by Verticillium.