Verticillium wilt is a fungal disease that attacks many tree species. Common symptoms include wilting and browning leaves, falling leaves and quite commonly, a whole side of a tree or a single branch of a tree dying off. Checking the sapwood under the bark of the infected branches, brown streaks may be observed. These symptoms are caused by a soil-borne fungus Verticillium albo-atrum, which begins in the root system and travels through the vascular system of the tree. This causes blockage and prevents water and nutrients from reaching all of the branches. The tree responds to this infiltration by plugging the infected tissues and this increases the blockage of water and nutrients, thus causing leaf wilting and branch death. Symptoms commonly occur in the middle of summer when the climate is dry and hot.
There is no fungicide treatment for Verticillium wilt. Once a tree or shrub is infected with Verticillium wilt, it will eventually die. Resistant species should be planted in place of it after it is removed. Observe a tree if it begins to develops symptoms, as opposed to immediately removing it. Trimming out the dead branches as well as keeping the tree watered and fertilized may delay the infection. Once a tree is infected, however, there is no curing it. The fungus that causes Verticillium wilt can affect many tree species, however yews and conifers are not affected. What is more, the fungus can thrive in the soil for many years, therefore if a maple for instance dies of Verticillium wilt and if the maple is removed, another maple should not be planted in its place, for the fungus is still present in the soil. Common susceptible trees species are ash, boxwood, catalpa, cherry, elm, lilac, magnolia, maple, redbud, serviceberry and tulip trees. Common resistant trees are apple, beech, birch, ginkgo, hornbeam, linden, oak, pear, poplar, rhododendron, sweet gum and walnut. For a complete list of Verticillium wilt susceptible and resistant plants, please check online.
A tree can become more susceptible to Verticillium wilt if environmental conditions are poor, such as if the tree is experiencing drought, girdling roots, compaction, scorch or nutrient deficiency. Any stress on a tree can more readily allow infection to take root or can cause a tree to decline more quickly. Depending on the tree and conditions, a tree may die in a single growing season from Verticillium wilt or a tree may decline over the course of many years.
If you think Verticillium wilt is present in your landscape, please call (616) 301-1300 ext 118 to schedule an appointment with one of our certified arborists. To make sure a tree is suffering from Verticillium wilt, Integrity can take a plant sample and send it to the Michigan State University plant diagnostic lab in order to get it tested. The sample must come from the infected area of the tree, as the fungus is not usually throughout the whole tree. Several different branches about 1 inch diameter thick of live tissue should be taken to ensure accuracy. The test will cost $75 and will take 1-2 weeks for results to come back.