Invasive Plant – Tree of Heaven – and how to control it

The following article about the invasive Tree of Heaven (Ailanthus altissima) is used by permission by the author Martin (Mort) Schmidt. It originally appeared in Simply Living’s Tree of the Month feature.

The section on control methods was written by FLOW member Bob Campbell.

Tree of Heaven

Mature Tree of Heaven. Photo by Mort Schmidt

The current Tree of the Month is a bad seed, if you’ll pardon the expression. If you’re someone who’s drawn to exotic beauties who are known troublemakers, Ailanthus altissima is the tree for you.

Tree of Heaven is native to China, and due to its hardiness, and in the eyes of many, its exotic beauty, it’s been naturalized worldwide. Like all invasive plants and animals, Tree of Heaven is perfectly well behaved in its native habitat. But while some species wither and die when they’re transplanted away from home, others go wild in the absence of competition and adversaries. Because of its hardiness and adaptability, this tree is often found on abandoned or neglected properties, growing up through drains and cracks in pavement.

Tree of Heaven has alternate, pinnately compound leaves, with 13 to 41 leaflets. (Pinnately compound leaves have leaflets attached to the stem at multiple points, whereas palmately compound leaves have leaflets attached at a single point, like the fingers in the palm of your hand). Leaflets are several inches long, have no lobes, and have smooth edges except for several teeth near the stem. The leaflets have a disagreeable odor when crushed – hence another common name, stink tree. The compound leaf is the largest of any found in Ohio, often several feet in length. Notice in the photograph that the compound leaf is longer than my torso! Because the compound leaf is so large, it leaves a huge scar when it falls off late in autumn. The horseshoe or heart-shaped scars are often larger than a quarter.

Left – Leaflets. Right – Compound leaves. Photos by Mort Schmidt.

Ailanthus can grow to a height of 80 ft with a trunk diameter up to 3 ft. Also owing to the immense leaf size, the twigs are unusually stout – typically the diameter of your pinky or even thumb. The bark on twigs and saplings is light brown and smooth, but becomes light gray and fissured on larger trees. Seeds typically appear on female trees in late summer and fall, and consist of twisted, reddish, 1.5″ samaras (wafers) with one seed. Large trees with seeds are recognizable from a distance by their reddish color.

Left – Leaf Scars. Right – Bark. Photos by Mort Schmidt.

Sumacs can be distinguished from tree of heaven by their toothed leaflets, agreeable odor, and berry-like fruits. Tree of heaven also resembles walnut, but a lengthwise slice in a walnut twig reveals chambered pith.

Left – Ailanthus Seeds. Right – Chambered pith in walnut. Photos by Mort Schmidt.

According to the Wood Database website, Ailanthus provides potentially useful lumber. It’s moderately hard, with a dry density of 0.60 g/cc, on par with white ash. It works well, readily takes stains and glues, and can be planed or sanded to a fine luster. Unfortunately, sensitive people are allergic to its dust and leaves. Its toxic properties are no doubt responsible for its natural resistance to insects.

According to Alice Thoms Vitale’s Leaves in Myth, Magic & Medicine, Tree of Heaven was brought from China to Europe to feed a species of silkworm after disease threatened the silkworms that fed on mulberry leaves. Ailanthus silk is tougher and cheaper than mulberry silk, but coarser and less glossy. An extraction of the leaves and bark was also ingested to drive out tapeworms.

The main problem with Tree of Heaven is that it also drives out native plants, due to its hardiness and its allelopathy – the production of chemicals that harm surrounding plants. Ailanthus also serves as a harbor for the invasive spotted lanternfly. This moth has piercing mouth parts that enable it to aggressively suck large volumes of sap from maples, walnuts, and other valuable trees. The lanternfly also exudes large volumes of a sticky, sugary substance that grows harmful fungus and attracts wasps. The lanternfly is poisonous to many predators, and it’s suspected of extracting its toxin from the tree of heaven. Tree of Heaven should be replaced with native trees, or simply removed. But, who knows? If we continue to destroy native trees with invasive pests, such as emerald ash borer and spotted lanternflies, we might be glad to have any trees at all!

Spotted lanternfly. Photo by Pennsylvania Department of Agriculture.

Control Methods for Ailanthus altissima (Tree of Heaven)

By Bob Campbell

Ailanthus is an important invasive tree to control promptly and effectively.  Larger trees are more difficult to treat, so its advantageous to monitor and kill trees while they are still small.  Ailanthus trees grow very rapidly, with sprouts growing six to twelve feet in their first year, and 3 feet or more each year after.  Furthermore, they can produce over 300,000 seeds per year, with stumps and roots that can sprout aggressively. They also produce allopathic compounds that suppress the growth of other nearby woody and herbaceous plants.

Ailanthus can be challenging to treat.  Cutting the tree down and treating the stump is NOT effective and should only be done when there’s a risk to human safety or potential damage to buildings.  When cut, ailanthus often produces numerous root sprouts, enhancing its spread!

For smaller trees under four and a half feet that cannot be mechanically removed, foliar spray with glyphosate or triclopyr is effective.  All the leaves should be sprayed but not to the point of producing runoff.  This is important to treat effectively but not harm other desirable vegetation..

For larger trees, basal bark spraying is recommended using a triclopyr ester formulation.  Herbicide should wet the bark from the root collar up 12 to 18 inches around the entire trunk.  However, for trees larger than 8” diameter (at 4.5 feet) may have thicker bark, so this method may not be effective.  The injection or “hack and squirt” method using a triclopyr salt (choline) will likely be more effective.  Cuts in the bark are usually made with a hatchet or similar tool and should be about one-half inch deep and one inch in length, with one cut per inch of trunk diameter.  A small amount of herbicide is placed in each cut.  Care should be taken so cuts aren’t so close together that the tree is girdled, resulting in sprouting.  But there should be no more than one inch between cuts.  There are reported instances where cuts that are two inches apart or more result in that part of the tree still surviving!

Here’s a video of the “hack and squirt”method by the UK forestry department:

Image from Rutgers Plant and Pest advisory; click image for article

Foliar treatment is more effective May through September, while leaves are green.  Basal bark and hack and squirt are generally most effective in mid-June through September.  Temperature can also be a factor, as temperatures warmer than 85 degrees can reduce effectiveness.  Other factors are also involved, as identical treatments sometimes yield different results.

Ailanthus trees should be monitored for several years to ensure effective treatment. And resprouting or trees not completely killed will need to be retreated.  Herbicide labels provide recommendations for chemical concentrations; application techniques and other guidance, should be carefully followed to ensure safety and maximal control. More information can be found at The Ohio State University Extension Services (ohioline.osu.edu) and the Ohio Department of Natural Resources, Division of Forestry (ohiodnr.gov/forestry), the primary sources for this article.

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