Tree of Heaven AKA Ailanthus altissima

                                  Ailanthus altissima With Flowers

                                    Ailanthus altissima With Seeds

I have yet to encounter this tree firsthand in our town, but I am told it is in fact growing here, and that is a serious issue.  Tree of Heaven is native to China where it has many uses in traditional Chinese medicine.  It is also a host there for a particular moth whose cocoons are used to produce silk.  The tree was first introduced to Europe in 1740 during a time when there was a great interest in Chinoiserie, a fancy word for Chinese influenced decoration. There it gained a positive reputation as a fast-growing shade tree. It was eventually marketed here in the U.S. as such.  Tree of Heaven was introduced to the United States in Philadelphia in 1784. Nobody was yet aware of the consequences, but over time its rapid uncontained spread throughout the United States has made it an invasive species.  It is considered invasive in Europe as well.  The tree got both the last part of its Latin name altissima which translates to very high, and its common name for its rapid upward growth, as though it were reaching for the Heavens.  I mean holy moly, this tree can grow up to eight feet in just one year, and it reaches a mature height of eighty to one hundred feet!  

                                               Staghorn Sumac

                                               Black Walnut Tree

In appearance, the tree strongly resembles several native trees including staghorn sumac, and black walnut trees.  Be cautious so as not to jump to conclusions and eliminate the wrong tree.  You may just be spotting an innocent bystander.  There are various methods that you can use to discern which tree you are dealing with.  There are differences in bark texture, flower structure and subtle variations in leaf structure, but a quick and definitive method of positive identification of tree of heaven is to rub a leaf between your fingers.  If the crushed leaf has a very unpleasant odor resembling rotten peanut butter with a little skunk odor thrown in, it is the invasive Tree of Heaven.  Mid-summer around July, if you are nearby when these trees are in bloom, you might also smell their strange perfume wafting through the air. The male trees produce abundant flowers that carry that unpleasant aroma which, believe it or not, attracts pollinators.  Not all pollinators are attracted to what we consider sweet fragrances!  The female trees of course also produce flowers although they are fewer in number.  As the growing season progresses, the female trees produce prolific dangling bunches of reddish-brown seeds.  To me at least, this is when the tree is most easily recognized.  The seeds ripen in September and fall gradually from the tree throughout the following months.  Each seed in the cluster is encased in a winged seedpod called a samara, similar to a maple tree seed.  These "wings" allow the seeds to travel great distances.  

The thing is, even without the seeds this tree has the capacity to reproduce.  Its roots travel horizontally, as far as 50 feet, creating new shoots that sprout into more trees. In this way Tree of Heaven can rapidly form colonies.  I often see large colonies of Tree of Heaven growing alongside various highways. Like some other plants that are now considered invasive, Tree of Heaven has allelopathic powers.  Portions of the tree create chemicals that are toxic to other plants.  These compounds suppress the growth of native plants encouraging the creation of a monoculture.  As you have likely heard in the news over the last few years, this tree is the host to vast numbers of the rapid breeding sap sucking Spotted Lantern Fly. This pest is an agricultural nightmare.  It is now found feeding on a variety of plants and trees.  With its capacity of killing them, it is especially harmful to both native and cultivated grapevines. Because Tree of Heaven is the Spotted Lantern Fly's natural host tree, and especially because of the Tree of Heaven's aggressive growth habits, this invasive tree is best removed as soon as possible after its discovery on town or private property.

HOW TO REMOVE - Read to the end!  Exciting news!!

Even young trees have a long tap root, making it difficult to hand pull them unless they are mere seedlings. If you are hand pulling young seedlings, be certain to remove the entire taproot as the plant can resprout from even a tiny fragment left behind.  The recommended method of removal of larger tree specimens without herbicide use is to cut the tree as low to the ground as possible.  Unfortunately, this will encourage sprouts to form, and they too must be cut as they appear.  It may take years of monitoring, cutting back emerging sprouts twice a year, but continued cutting of new sprouts should eventually deplete the strength of the root system and eliminate the plant.  

If you are comfortable using herbicides, the herbicide of choice for this tree is Triclopyr.  Over the course of time, different methods have been recommended.  Presently, the most effective method of killing a large tree without encouraging sprouting from the root is to make downward hatchet strokes in a perforated pattern around the trunk of the tree into the cambium layer. The cambium layer is the portion between the bark and the central portion of the tree.  It is the part of the tree that channels nutrients to the crown of the tree, and back to the root.  Apply a concentrated solution of Triclopyr in the pockets you created around the tree.  You may need a second application after several months.  Over time this will gradually weaken and kill the tree.  Another method involving herbicides still being used, especially if the tree is tall and in a dangerous place where you need to control its fall, is to cut the tree as low to the ground as possible and paint the stump with a concentrated solution of Triclopyr.  Painting the stump helps to prevent the stump from resprouting.  The root system will send up sprouts as a reaction to the tree being cut down, and you will have to address the resultant sprouts by using a spray in 8% strength of Triclopyr.  The foliar spray should be applied after the leaves of the sprouts have fully matured. 

Possible future biological control - Samia Cynthia AKA Ailanthus silk moth, native to China, is a pretty moth with crescent decoration on its large wingspan.  This moth lays its eggs solely on the Tree of heaven.  The moth's larvae when hatched, can quickly consume a vast amount of foliage from this tree though they will consume other foliage as well.  The moth's distribution in Connecticut is fairly spotty at this time.  I imagine their population will increase along with Ailanthus altissima as time progresses.  Hopefully that will be a good thing!

The really exciting part! - I recently found exciting information about a fungus I wanted to share, because who wouldn't be excited about a fungus right?  This one, first recognized as a potential slayer of Ailanthus altissima in 2024, seems to have originated in the soil in Pennsylvania and Ohio. It's called Verticillium nonalfalfae. It causes Ailanthus wilt which, exactly as it sounds, first presents as wilting foliage, and then as a yellow brown discoloration of the wood directly below the bark. The fungus rapidly causes death to the tree. The fungal disease passes easily from root to root contact so a single application can eradicate an entire colony of Ailanthus Altissima. In addition, the fungus can be moved from infected trees to healthy trees simply by moving an infected portion of root into contact with healthy roots.  There does not appear to be any significant negative effect to native vegetation, although this fungal disease does negatively affect the hops plant. Use of Verticillium nonalfalfae as what is essentially a natural herbicide active against tree of heaven is presently in the research stage and not yet available for public use, but once it is approved, there is hope that repetitive chemical herbicide application to eradicate tree of heaven will no longer be necessary.