Extension educator: Late summer, early fall optimal time to treat tree of heaven

The Ailanthus altissima tree — better known as tree of heaven — is an invasive tree and noxious weed in Pennsylvania. Credit: David JacksonAll Rights Reserved.

UNIVERSITY PARK, Pa. — Like the spotted lanternfly that has a penchant for it, the rapidly growing Ailanthus altissima tree — better known as tree of heaven — can be tough for property owners to control.

“This is not your ordinary tree — it is difficult to eliminate due to its prolific seed production and root-sprouting ability,” said Penn State Extension educator David Jackson, who specializes in forest resources management. “Tree of heaven requires specific control measures to eradicate, and now is a perfect time because late summer herbicide applications work best.”

Tree of heaven originally was introduced to Philadelphia in the late 1700s for use as an urban street tree. It also was planted widely in the Baltimore and Washington, D.C., areas. From these regions, it spread and became a common invasive plant in urban, agricultural and forested areas.

The species is dioecious, meaning a tree is either male or female and usually grows in dense colonies or “clones.” Female trees are prolific seeders with the potential to produce more than 300,000 seeds annually. These seeds are dispersed by the wind throughout the fall and winter.

Once established, tree of heaven continually spreads by sending up what Jackson described as “root suckers,” which can emerge as far as 50 feet from the parent tree.

“Tree of heaven can sprout anywhere, including in sidewalk cracks,” said Jackson of the species, which can reach 80 feet in height and 4 feet in diameter. “It does not provide useful wood products or food for beneficial insects and other wildlife. In short, it does more harm than good.”

While people might not be enthralled with tree of heaven, the same is not true for the ravenous spotted lanternfly, another invasive species. The insect’s attraction to the tree’s sap as a food source has led to a control tactic that involves destroying a high percentage of tree of heaven trees on a property with herbicides and using those remaining as “trap” trees.

These trap trees are treated with a systemic insecticide, either a soil drench, injection or a bark spray, which is absorbed by the tree and then ingested by feeding spotted lanternflies.

While the trap tree method is useful for killing spotted lanternfly, Jackson said the method works best for property owners with individual tree of heaven yard trees or a small clonal patch. “It is challenging for those without forestry or landscaping expertise to deal with a large colony of trees because the root systems are so aggressive and difficult to control.”

Timing is essential when using tree of heaven as a trap tree. “If you apply an insecticide too early in the season, you will destroy some nymphs,” Jackson said. “But by September, when the adults are swarming, that same insecticide may have lost its effectiveness and cannot be applied again due to label specifications. My recommendation is to target spotted lanternfly adults and use the trap tree method in late summer to prevent female spotted lanternflies from laying eggs.”

Property owners are encouraged to learn how to identify tree of heaven and take measures to control it, especially the female trees, which have yellowish-red seed clusters hanging from their branches now.

Female tree of heaven produces yellowish-red seed clusters. Credit: David JacksonAll Rights Reserved.

“There is misinformation out there on how to get rid of tree of heaven,” Jackson said. “Many people make the mistake of simply cutting it down, which triggers the root system to send up hundreds of sprouts.”

He said the best way to control the tree is to target the roots with systemic herbicides when the tree is moving carbohydrates to the roots. This takes place from July until the onset of fall color.

Herbicides applied to foliage, bark or cuts on the stem all are effective. He recommends cutting the tree and treating the stump only as a last resort as his studies have shown that this kills the stump but does not control the roots.

There are many herbicides available for use on tree of heaven, Jackson noted. It is important to follow all instructions on the label and to use the proper concentration — ready-to-use formulations with only 1% to 2% active ingredient are not sufficient.

Penn State Extension has photos, fact sheets and videos on tree of heaven control, which can be found here.

Last Updated August 20, 2020