Verticillium wilt is one of the most common and destructive diseases of shade and ornamental trees in Indiana. Redbud and hard maple trees are especially susceptible. In addition, Verticillium wilt attacks more than 80 other different tree species and many other plants, such as potato, tomato, rose, lilac, and snapdragon. In all, more than 300 plant species have been reported susceptible to this disease. Yews and conifers do not appear to be susceptible.
During midsummer, leaves turn yellow at the margins, then brown and dry. Sudden wilting of leaves on one or several branches may occur. Frequently, the foliage on only one side of a tree wilts. The wood under the bark of wilting branches is discolored in streaks. The discoloration will vary from bright olive-green (maples) to chocolate-brown (redbud), depending upon the tree species and how long it has been infected. The discoloration might occur as distinct bands, streaks, or flecks in the sapwood. To examine for discolored sapwood, cut into the outer sapwood at the base of branches showing leaf wilt; also examine the outer rings of wood at the cut end of a pruned branch for signs of discoloration.
Host susceptibility and environ mental conditions influence severity of symptom development. Trees under drought, nutrient, or salt stressare 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.
The soil-borne fungus, Verticillium albo-atrum, causes Verticillium wilt. 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.
Sourced from the Purdue University Cooperative Extension Service