Tree of Heaven
AKA Stink Tree, Chinese Sumac, or Stinking Sumac (Ailanthus Altissima)
Tree of Heaven is a fast-growing prolific seeder that pushes out native plants. Its allelopathic effects make the ground toxic to other plants. Root sprouts can appear 50-90 feet from the parent stem. It causes damage to sewers, pavement, and structures.
Although Benton County Noxious Weed Control Board does not enforce this tree as a noxious weed, Tree of Heaven is considered a Class C Noxious Weed in Washington State. Do not plant this tree,and warn others about the dangers of transplanting this species.
How to Control Tree of Heaven
The best method depends on the age and placement of the tree. Mechanical methods no matter the size of the infestation can be a good first step in Tree of Heaven control. But follow-up treatments; whether they are chemical methods or mechanical methods, are required. Prescribed fire is not recommended to control tree of heaven because like other top-kill treatments, it stimulates root sprouts.
The Challenge:
Tree of Heaven is difficult to control once it’s become established. The root system is almost impossible to remove, and even a small root fragment can produce sprouts. Root suckers can emerge several years after a disturbance. It re-sprouts when cut and sends out root suckers even when herbicide is used. Elimination will require diligence.
The Game Plan:
Target the female trees first. This will help prevent spread by seed. Start on the outside of the infestation and work your way in. Once you start your initial treatment; monitor the area at least twice a year (particularly in June and September) for new sprouts. Then treat any new sprouts as soon as they appear. This will ensure that the plants do not have time to build up carbohydrate reserves it its root system again. Once it appears that the tree of heaven is controlled, monitor the site for at least another year just to be sure.
In small areas, seedlings can be controlled by: hand pulling, digging, or using a weed wench before seed production in August, followed by removing all root fragments to prevent re-sprouting. Monitor the area for new sprouts as described in the game plan, in case you have missed fragments or until the seed bank is depleted.
A large infestation will likely need to be controlled with herbicide; the longer that this tree has been established, the larger the root reserves will be. Always follow herbicide labels. Systemic herbicides that kill the roots are the best chemical control for Tree of Heaven. This will carry the herbicide through the tree and reduce new suckers and sprouts. Be careful as Tree of heaven roots may exude herbicide and herbicides meant for Tree of Heaven may kill non-target trees even when injected into stems. There are many ways to apply herbicide to Tree of Heaven. These are a few suggestions:
The hack and squirt method: First you use an axe to make a series of cuts around the tree truck at about the same level, then immediately apply concentrated herbicide in each of the cuts.
You can cut the tree down, and immediately apply herbicide to the stump. The best time to do this is July through to mid-September. On the other hand, it can be even more effective if you can do it twice; once in March-June to allow the stump to sprout, and then again in July-early September to further deplete its carbohydrate stores in the root system.
Basal Bark applications, or stump applications in November-January can reduce the risk of contaminating non-target plants.
Herbicides alone are not a complete or long-term solution. You will need to change the condition that allow infestations to occur. Tree of heaven sprouts do not like shade, so unless the area is heavily shaded you will need at least 5 years of follow-up mechanical treatment to control sprouts.