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James A. Chatfield, Ohio State University Extension, Northeast District/Horticulture and Crop Science; Nancy A. Taylor, Erik A. Draper, Stephen Nameth, Joseph F. Boggs, |
BYGLive! participants in Cincinnati spent some time viewing a smoketree that exhibited classic symptoms of Verticillium wilt disease (Verticillium albo-atrum). Leaves were becoming scorched, drooping, and eventually turning brown while remaining attached to the tree. An examination of the affected branches revealed vascular streaking in the conducting system of the plant's stems.
The Verticillium fungus has a broad host range of plants that it infects, including many common woody ornamentals. A partial list of common susceptible hosts includes ash, azalea, barberry, catalpa, cherry and other stone fruits, daphne, elm, honeysuckle, lilac, magnolia, maple, Russian olive, peony, privet, redbud, rose, serviceberry, smoketree, spiraea, tree-of-heaven, tuliptree, viburnum, and yellowwood.
Plants with good resistance include all gymnosperms (pine, spruce, fir, hemlock, yew, ginkgo, etc.), and all monocots (grasses, sedges, lilies, palms, etc.). A partial list of other resistant plants includes mountainash, beech, birch, crabapple, dogwood, sweetgum, hackberry, hawthorn, hickory, holly, linden, honeylocust, oak, pawpaw, pear, planetrees, rhododendron, walnut, and willow.
The Verticillium fungus infects plants through the roots, moving upward by means of the vascular system. Environmental factors that affect Verticillium infection and subsequent disease development include moisture stress, root injury, damage from salts, transplant injury, and other factors that affect root health.
Indeed, the factors affecting wilt incidence and severity include all three angles of the disease triangle:
The BYGLive! participants discussed what should be done, and the first conclusion was that the disease should be confirmed by sending proper samples to the PPDC. While the smoketree appeared to have all the "right" symptoms, other problems can cause exactly the same symptoms. For example, streaking of the vascular tissue can be caused by other nonpathogenic fungi. On the other hand, some trees, such as ash, are notorious for confusing the issue by seldom expressing this vascular discoloration symptom of a Verticillium infection.
Samples sent to the Clinic for confirmation should include twigs with entire leaves that are still attached to the tree, but exhibit scorch symptoms. The fungus may be isolated from the leaf petioles. To allow for isolation of the fungus from branch tissue, 6" to 8" sections of wood about 0.75"-1" in diameter taken from branches with scorched leaves, should also be sent. As with all samples sent to the Clinic, it is best to send them early in the week and by "overnight" delivery.