Verticillium is a fungus that causes Verticillium wilt in over 300 plants, involving many plant families. Both Verticillium dahliae and V. albo-atrum species are found in Illinois soils. We commonly see it at the University of Illinois Plant Clinic on tomatoes, smokebush, maple, redbud, and magnolia. If you think your plant is infected, first find out whether that species is a host. Then compare symptoms to those described in the Report on Plant Disease (RPD), no. 1010, “Verticillium Wilt Disease,” available online at http://www.ag.uiuc.edu/~vista/abstracts/a1010.html. Typically, we see all of the leaves on one tree branch turn brown or large areas of a plant with wilted or brown foliage. The image shows a maple tree that is infected with Verticillium wilt.
This fungal genus is persistent. It may remain alive in the soil for many years in a resting state. Infected trees may die quickly in one season or slowly over several years. If detected early in large trees, the disease may be kept in check by pruning; but usually the disease causes plant death. Positive identification is helpful in planning replacement trees and shrubs. Resistant plants are available, but choices are few. This disease is a problem on woody and herbaceous hosts, so learn the symptoms and signs. Chemicals are not generally considered an option in the landscape.
When submitting a sample to the University of Illinois Plant Clinic for Verticillium testing, be aware that the sample must contain vascular discoloration, or we will not continue with isolations. The only exception is ash. That species may be infected without exhibiting vascular discoloration. For all other samples, find live wood from branches or stems that show green to brown staining of the vascular tissue, as shown in the image of infected maple stems.
Send sections with bark intact, not peeled off the stem. Often the Verticillium fungus takes 10 to 14 days to grow in culture to the point where it can be positively identified, so be patient. For other details on submitting samples to the University of Illinois Plant Clinic, visit our web site at http://plantclinic.cropsci.uiuc.edu/.