Tree of Heaven Wears Out Its Welcome
What’s a weed, anyway? They say a weed is simply a plant growing where it’s not wanted, which pretty well describes the Tree of Heaven (Ailanthus altissima). You’ve seen it, whether you know it or not, because Tree of Heaven is found throughout the Columbia River Gorge – along road edges, backyards, alleys, edges of parking lots, empty lots, cracks in sidewalks.
Tree of heaven has also been around a long time, brought from China and introduced by travelers and officials seeking hardy street trees, and planted (along with locust and Russian olive) by the hundreds or thousands from The Dalles eastward by Sam Boardman, Oregon’s enterprising and energetic Superintendent of State Parks in the 1930s and ‘40s. Ailanthus was favored for its toughness. It can seemingly grow anywhere and quickly! Dense or sandy soil? Fine. Full sun or part shade? Yes. Drought conditions, deserts with low rainfall? No problem.
Despite its hardiness, Tree of Heaven has many undesirable qualities. It’s an aggressive grower, spreading vegetatively by sending out sprouts, often damaging paved areas, home foundations or underground utilities. While growing quickly, its wood has very little value, not as firewood or long-lasting shade; it is considered a tree-fall hazard. It often forms thickets, displacing native trees, and providing little or no habitat for birds, butterflies, or beneficial bugs. The tree can also be toxic and leaches allelopathic chemicals that may inhibit the growth of or kill neighboring plants.
Tree of heaven is a bully of a plant that does not play well with others and has worn out its welcome. It outcompetes and crowds out native and cultivated vegetation, and it is the preferred host for another invasive pest, not yet arrived to the area, the Spotted Lanternfly. State agriculture and noxious weed authorities are beginning to take notice. Locally, Underwood Conservation District is organizing the “Tree of Heaven Control Project” with partners at Yakama Nation Fisheries, the Cities of Bingen and White Salmon and county Noxious Weed Control. With funding from the State of Washington Department of Natural Resources Urban and Community Forestry Program and the Columbia Gorge Cooperative Weed Management Area, UCD is launching outreach around this weed tree and lending support to cities and homeowners who would like to remove Tree of Heaven.
One primary reason for controlling Tree of Heaven is that it is the preferred host for the Spotted Lanternfly (Lycorma delicatula). This piercing, sucking insect, which like Tree of Heaven is native to Asia, is a new and emerging pest in the U.S. for a wide variety of important agricultural crops, including grapes, apples, cherries, hops and many more that are also important to the regional economy. If established here, the Spotted Lanternfly could cost the state’s agricultural industry $3 billion annually. The WA State Dept. of Agriculture and the WA State Invasive Species Council are working to develop a statewide Spotted Lanternfly Action Plan and Early Detection/ Rapid Response Strategy.
Another outcome of large populations of the insect is its habit of coating cars, decks, pets, and plants with excessive quantities of a sticky excretion called honeydew. The honeydew is excreted sap from the trees the Spotted Lanternfly feeds on, having pierced them with its sucking mouthparts, which also attracts other insects and produces a sooty mold. If introduced, the Spotted Lanternfly will feed on dozens of tree species, including maples, willows, and fruit trees. The bottom line is, we don’t want the Spotted Lanternfly making its home here.
The first step to reducing the preferred habitat for Spotted Lanternfly and controlling Tree of Heaven is to properly identify it. The tree has compound leaflets on each branching leaf similar to a walnut, ash or sumac, but one key difference is that the Tree of Heaven leaf has a smooth edge, while the others have serrated, or toothed, edges. Snapped twigs and crushed, fresh leaves smell like rotten peanut butter. Tree of Heaven readily sends out many underground suckers and often grows in dense clumps. It has smooth bark, even fuzzy when young, that turns gray and develops shallow, diamond-shaped fissures when mature. Tree of Heaven seeds are in clustered, papery wings, dispersed by wind and birds, while walnut trees have walnuts and sumacs are distinctive by their red fuzzy spikes. One mature female tree can produce about 325,000 seeds annually! This map shows some known locations of the tree in our area.
Getting rid of Tree of Heaven isn’t always easy. Young seedlings can be pulled out before they’ve developed a long, strong taproot. Dispose in the landfill or by burning, but not composting at home. Cut stems can grow roots if left on moist ground. Larger infestations will take persistence and/or herbicides to remove. Do not just cut or mow Tree of Heaven: it will prolifically sucker, and you’ll end up with a hydra-headed nuisance. Some roots can extend as far as 50 feet underground before sprouting upwards again. Since cutting the tree and then treating the cut stump with herbicide can simply encourage more root suckering, specific herbicides and application methods should be carefully observed in mid-late summer. Always follow pesticide labels and read specific guidance; for more detailed treatment methods consult this link: https://columbiagorgecwma.org/weed-listing/best-management-practices/tree-of-heaven/
Tree of Heaven can cause skin irritations or allergies in some people. Wear gloves when pulling or handling, and avoid skin contact with the sap.
Sound like too much? Never fear: Underwood Conservation District (UCD) and partners can provide removal assistance for local residents, and help you replace the Tree of Heaven with appropriate native and locally-adapted trees. One desirable native tree is the grand Oregon White Oak (Quercus garryana).
Interested in assistance removing Tree of Heaven from your property? Not sure if you have it? Want to help share information to your neighborhood? Watch UCD’s website for program details (www.ucdwa.org) or contact UCD to start the conversation (email toh@ucdwa.org).