Fortunately, the fungus is not able to grow into adjacent cells except where the cells are connected end to end. Thus, spread of the pathogens within a tree is slow, and large infected trees take many years to die. Small trees, however, may be killed in a single season. Control of Verticillium wilt is difficult because the pathogens live in the soil and form microscopic resting structures that are resistant to conventional fungicides. Diseased trees show dead and dying branches, sparse crowns, and sharply reduced twig growth in addition to the leaf symptoms.
Branches frequently die during the dormant season.
Plants that show limited branch symptoms one year may show additional wilt and branch die back next year, or they may recover and be symptom-free for one to several years. Rarely, entire plants die within a few weeks during the growing season. Stunting caused by chronically reduced growth is common and may occur in the absence of other symptoms in some plants such as elms that are tolerant of infection. Within the plant, species of Verticillium cause a discoloration that appears as streaks or bands in the sapwood. The color of the streaking varies among different species of plants.