publication 450-619 Verticillium Wilt of Shade Trees R. J. Stipes, Professor of Plant Pathology M. A. Hansen, Extension Plant Pathologist, Department of Plant Pathology, Physiology and Weed Science, Virginia Tech,

Verticillium wilt is a serious vascular wilt disease that commonly extend from the roots into the branches. In a affects a broad array of shade tree species. The fungi slant cut the discoloration appears as spots or partial to that cause Verticillium wilt, Verticillium albo-atrum complete rings in one or more growth rings (Fig. 2). The and V. dahliae, are soil-borne and infect through the discoloration varies with the tree species. In maples and roots. They can gradually become systemic in the tree. smoketree, it is grayish-green to olive-green; in black These fungi are capable of attacking over 130 different locust, it is brown to black; in elm, it is brown; and in species of shade and ornamental trees, food and fiber northern catalpa, it is purple to bluish brown. Streak- crops, and herbaceous ornamentals. Because these ing may or may not be found in affected branches, and fungi are soil-borne and can infect so many different observation of the wood in or near the root system may plant species, Verticillium wilt is difficult to control. be required. Positive confirmation can be made only by laboratory culture of symptomatic wood samples. Symptoms Once the fungus gains entry to the tree through the root system, it generally spreads upward into the trunk through the sapwood and interferes with water move- ment and other plant functions. It causes a variety of symptoms that may be accentuated by drought, inad- equate nutrition, poor drainage, or other con- ditions that reduce tree vigor. Wilting, interveinal browning, and leaf drop usually begin on one branch or on a Fig. 2. Leaf symptoms and vascular discoloration in sapwood of section of the tree sugar maple. (Photo by R. J. Stipes) and progress through- out the tree. Dead and dying branches, sparse- Control ness of the crown, and The fact that Verticillium species are able to attack reduced twig growth both herbaceous and woody plants complicates control. are frequently ob- Verticillium-susceptible weeds, such as lamb’s quar- served (Fig. 1). ters, amaranth (pigweed), nightshade (horse nettle), and ground cherry, are hosts of the fungus and should Verticillium spe- Fig. 1. Symptoms of Verticillium wilt cies cause discolored on maple: the left half of the tree be controlled. In nurseries, rotation of susceptible and streaks in the sapwood appears diseased, while the right half nonsusceptible species is recommended. Certain plant appears healthy. parasitic nematodes are capable of interacting with that run parallel to the (Photo by R. J. Stipes) grain of the wood and Verticillium spp. to increase the incidence and severity

www.ext.vt.edu Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 2009 Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. RIck D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg. of disease in susceptible shade tree seedlings. Nema- • Prune out dead branches to prevent infection by other tode control, therefore, is recommended in nurseries pathogens. where Verticillium wilt is known to occur. Nematode • Remove and replace severely infected or dead trees control currently involves use of a preplant nematicide with a wilt-resistant species (Table 1). or soil-sterilant and is usually not practical in home landscape situations. Susceptible and Resistant Hosts The following disease control measures are recom- Maple (Acer) species are probably the best known shade mended for landscape plantings: tree hosts of Verticillium spp. Silver (A. saccharinum), Norway (A. platanoides), red (A. rubrum), Japanese (A. • Make a positive laboratory diagnosis. palmatum), and sugar (A. saccharum) maples are com- • Apply a liberal and prompt application of ammonium monly infected. Other woody species reported to be sulfate fertilizer to trees with mild symptoms. (Stud- either susceptible, resistant, or immune are reported in ies in Michigan showed that nitrate fertilizers were Tables 1 and 2. ineffective.)

Table 1. Table 2. Species resistant or immune to Verticillium wilt Species susceptible to Verticillium wilt Abies spp. (fir) Acer spp. (maple) Amelanchier spp. (serviceberry) Aesculus hippocastanum (horsechestnut) Betula spp. (birch) Ailanthus altissima (tree-of-heaven) Buxus spp. (boxwood) Catalpa speciosa (northern catalpa) Carpinus spp. (ironwood) C. bignonioides (southern catalpa) Castanea mollissima (Chinese chestnut) Cercis canadensis (redbud) Ceanothus spp. (red-root) C. siliquastrum (Judas tree) Celtis spp. (hackberry) Cotinus coggygria (smoketree) Cercidiphyllum japonicum (katsura-tree) Cydonia oblonga (quince) Cornus spp. (dogwood) Diospyros virginiana (persimmon) Crataegus spp. (hawthorn) Fraxinus pennsylvanica (ash) Fagus spp. (beech) Juglans regia (English walnut) Ficus carica (fig) Koelreuteria paniculata (goldenrain tree) Ginkgo biloba (maidenhair tree) Liriodendron tulipifera (tulip tree) Gleditsia spp. (honey locust) Populus tremula (European aspen) Ilex spp. (holly) Robinia pseudo-acacia (black locust) Juglans spp. (walnut) Sassafras variifolium (sassafras) Juniperus spp. (juniper) Ulmus americana (American elm) Larix spp. (larch) U. procera (English elm) Liquidambar styraciflua(sweet gum) U. rubra (slippery elm) Malus spp. (apple) Morus spp. (mulberry) Nerium oleander (oleander) Picea spp. (spruce) Pinus spp. (pine) Platanus spp. (sycamore) Pyracantha spp. (fire-thorn) Pyrus spp. (pear) Quercus alba (white oak) Q. falcata (southern red oak) Q. phellos (willow oak) Q. virginiana (live oak) Salix spp. (willow) Sorbus aucuparia (European mountain-ash) Taxus spp. (yew) Zelkova serrata (zelkova) 2