Verticillium wilt is a common disease caused by the soil fungus, Verticillium dahliae.
Several woody plants can be affected such as:
Usually the fungus infects plants through roots, but sometimes can enter through aboveground wounds. It can survive in the soil for several years.
Yellow and wilted leaves that typically appear on a single branch or section of the crown are symptoms of Verticillium wilt. Disease progression can be slow, taking months or years. Other times affected leaves dry and turn brown then fall from the tree quickly, within days or weeks. The disease causes water-conducting cells to be blocked and turn black or greenish-black. This streaking may be observed in branches after peeling away the bark. Leaf symptoms and streaking are good clues that Verticillium wilt may be the culprit. However, a positive diagnosis can only be made after growing the fungus from a sample. To submit a sample to the Iowa State University Plant Disease Clinic , collect sections from affected branches that are approximately 1/2 inch in diameter and six inches long. Collect samples only from branches actively displaying symptoms. Please, do not send in dead, deteriorating branches. Place the sample in a plastic bag and ship as soon as possible. There is a $10.00 Clinic fee.
Disease progression may be slowed in trees or shrubs with mild symptoms by providing adequate soil moisture and fertilizer. Pruning dead or dying branches or twigs is recommended. If replanting in the area, selection of resistant plants, such as hawthorn, conifers, white oak, or flowering crabapple can help to avoid another Verticillium wilt episode.
This article originally appeared in the June 29, 2001 issue, p. 83.
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