May Weed of the Month: Tree of Heaven

Tree of heaven (Ailanthus altissima) is a fast-growing, prolific seed producer that was listed in Minnesota as a Restricted Noxious Weed beginning in 2017. It is native to China and was brought to North America in the late 1700s as an ornamental shade tree. In urban areas, it can cause damage to sewers, pavement, and building foundations; in natural ecosystems, it can establish dense monocultures that outcompete native plants.

Tree of heaven looks similar to staghorn sumac, ash, and walnut trees. It can reach heights of 70 feet and has compound leaves that can be 1-4 feet in length with 11-41 leaflets. The flowers are small, yellowish-green, and arranged in large clusters at the ends of the leaves. It produces winged fruit similar to maple trees that hang in long clusters. The fast-growing, horizontal roots can send up new sprouts up to 90 feet from the parent stem. Tree of heaven also emits a strong, offensive odor that helps distinguish it from other plants.

Though there is only one documented tree of heaven in Minnesota, it has the potential to become invasive in the state. It is highly adaptable and tolerant of disturbance. Because of its tolerance to pollution and tight rooting spaces, it has been planted in many urban areas. Several guidelines may be used to manage and prevent it from spreading:

• Once established, tree of heaven is difficult to control. For all management options, infestation sites will need to be monitored and treated repeatedly until the seedbanks and rootstocks are depleted.

• Be sure to confirm identification before controlling, so you do not mistake a native species like staghorn sumac. Pay special attention to controlling female trees to reduce seed production.

• Do not plant tree of heaven or spread its seeds when moving soil from infested areas.

• Small infestations can be controlled manually by pulling and digging. Very young seedlings can be pulled easily by hand. Be sure to remove the entire root to prevent resprouting.

• Large infestations can be controlled with either foliar or cut-stem herbicide applications. For specific herbicide recommendations, contact your University of Minnesota Regional Extension Educator.