Tree of Heaven Management and Monitoring
Tree of heaven is difficult to control.
Hand pulling seedlings and all of the roots will work (any left behind root fragments can regrow).
Cutting down or girdling these trees is insufficient. Mechanical control of anything other than seedlings will cause TOH to sprout from trunks or roots, whereby making the problem worse.
The fungus Verticillium nonalfalfae (Vn) shows promise in controlling Ailanthus and is fairly host specific.
Insect pests (particularly spotted lanternfly - which is a invasive and exotic pest in the United States) can damage or even kill individual trees, but not a means of widespread control.
Systemic herbicides targeting roots should be applied no earlier than July 1st in Pennsylvania through September (or up until tree shows fall color) when photosynthates are moving to the roots. Timing before or after this time will result in a waste of time, product, and energy.
Allow 30 days for herbicides to fully work and make sure it has killed the tree before any attempt to cutting it down. *do not apply herbicides directly to cut trunks.
Herbicides can also be applied to leaves, stems and bark.
Herbicides sprayed to leaves should be done when the trees are smaller and full coverage without drift can occur. Spray can be done with a "high-volume truck-mounted sprayer" or "low-volume backpack sprayer."
Sometimes two applications are necessary if there is a dense population. First spray the leaves and allow them to dieback. Then a second spray applied to target the stems.
Basal bark applications work for targeting trunks less than 6 inches in diameter. It should be applied from the ground to about 12 to 18 inches high.
Hack-and-squirt technique is done to the trunk and can be a highly selective as well as effective way to control tree of heaven. This technique requires applying herbicides to frill cuts that are made around the circumference of the stem1.
Large stands of tree of heaven are the most difficult to control and likely need repeated herbicide applications and monitoring. Although continued monitoring is critical in any instance where herbicide is applied to tree of heaven.
Monitoring, Mechanical, and Chemical Control:
Invasive weeds fact sheet Tree-of-Heaven (Ailanthus altissima). 2018. PennState Extension. Available from https://extension.psu.edu/tree-of-heaven
Ailanthus and Verticillium nonalfalfae. 2017. USDA Forest Service: Northern Research Station. Available from https://www.nrs.fs.fed.us/disturbance/invasive_species/ailanthus_and_Vn/