Invasive Tree: Ailanthus altissima

21 September 2004

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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Maybe you call it tree-of-heaven, tree-of-paradise, or stink-tree, but its scientific name is Ailanthus altissima. Those who regularly battle Ailanthus have been overheard using some other names as well. The Ailanthus problem is well known among natural resource managers who classify Ailanthus as an invasive exotic: invasive because the tree spreads rapidly and has few insect or disease pathogens and exotic because this species is not native to the U.S. Among invasive exotics, Ailanthus is especially notorious due to its ability to quickly invade disturbed areas and resist control efforts.

Introduced from Asia to the U.S. in 1784, Ailanthus was originally used as an urban landscape tree and later to stabilize construction sites. However, like many introduced species, Ailanthus quickly escaped from its intended uses and has since spread to every region of the U.S. Ailanthus is able to withstand pollution and stabilize erosion prone road cuts but that is where the benefits end. Ailanthus has invaded urban and rural forests alike, displacing thousands of acres of native vegetation and offering little or no economic or wildlife benefits in return. And, it is spreading.

Ailanthus can be easily confused with sumac (Rhus typhina) and young black walnut (Juglans nigra). Ailanthus leaves are pinnately compound (i.e., they have multiple leaflets on a single leafstalk). Leaves are typically 12 to 24 inches long and unlike walnut have an odd number of leaflets (between 11 and 25). One to four lobes distinguish the bottom of each leaflet with gland-dots at the tip of each lobe. Twigs and stems are light brown and covered with tan bumps or lenticels. The pith or inner core of the twig is a spongy brown color (compared to the dark brown chambered pith of walnut) and produces the odor from which Ailanthus earns the name stink-tree. Twigs and branches break easily which aids in identifying pith color and odor.

Like eastern redcedar (Juniperus virginiana) and Virginia pine (Pinus virginiana), Ailanthus is considered a pioneer species, a plant that is generally shade intolerant and grows rapidly on disturbed sites such as fallow agricultural lands, field and forest borders, recently harvested forest stands, road cuts, and right-of-ways. Ailanthus spreads prolifically from seeds, stumps, and roots. Mature female trees produce up to 300,000 windborne seeds each fall. Both male and female trees propagate quickly from root suckers and stump sprouts and can reach 9 to 12 feet in their first year of growth. Seedlings and sprouts rapidly form pure stands by outgrowing surrounding vegetation and by producing an allelopathic compound that suppresses many native woody and herbaceous species.

Current control methods for Ailanthus can be broadly characterized as physical and chemical and may be approached differently depending on the size of the Ailanthus population. Before control measures are undertaken it is crucial to consider how the reclaimed site will be used and that the desired tree species be established soon after Ailanthus is initially controlled. Landowners must always remain vigilant for reemerging populations of Ailanthus.

Physical control methods include cutting, removal of roots, burning, and mowing. Cutting alone will not kill Ailanthus. In fact, the tree will vigorously resprout from the roots and stumps and will result in many more stems than were initially cut. Digging roots is practical only for very small patches, as all traces of root must be removed. Similar to cutting, burning and mowing kill only the above ground stems, and trees will resprout from the roots. Because root removal is extremely labor intensive, and burning and mowing are non-selective, cutting is usually the preferred method of physical control. However, cutting is only effective when coupled with chemical control.

The best control will result from a late growing season combination of physical and chemical control that begins by cutting trees before they have produced and scattered their seed. For the homeowner with one or a few trees to control, the easiest method is to cut the tree down and apply full strength glyphosate to the top of the cut stump. Glyphosate is sold under the trade name Roundup and others now that the patent has expired. For the landowner with a larger area to manage, two types of herbicide, imazapyr and triclopyr have proven very effective in controlling Ailanthus. Imazapyr is sold under the trade names Arsenal (water-soluble salt) and Stalker (oil base) and triclopyr under the trade names Garlon 3A (water-soluble salt) and Garlon 4 (oil base). Both water and oil based mixtures have benefits and drawbacks. In general, water-soluble mixtures are easier to mix and clean, and break down more quickly in the environment. On the other hand, while more difficult to clean up and longer lasting in the environment, oil mixtures are usually more effective in penetrating bark and leaves.

To be safe and effective, herbicide use requires careful knowledge of the chemicals, appropriate concentrations, and the effective method and timing of their application. For more details, read the herbicide label.

Despite effective cutting, burning, and use of herbicides, Ailanthus can quickly reestablish itself by airborne seed from neighboring properties. You might share this information with your neighbors and encourage them to eradicate their Ailanthus populations as well. You might also consider sharing the costs of equipment, herbicides, and application with your neighbors.

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For more information on gardening, contact your local Virginia Cooperative Extension office. Many county Extension offices have a help desk that is staffed by Master Gardener volunteers. These volunteers are trained to answer questions about garden and landscape topics. The local Virginia Cooperative Extension office numbers are Albemarle 984-0727, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.