Ailanthus altissima (Tree-of-Heaven, ToH) is listed as invasive in Connecticut. In

addition to forming large clonal colonies that crowd out native trees and understory

plants, ToH produces allelopathic chemicals that inhibit the germination of most

native plants. Mature female ToH trees can produce more than 300,000 winged

seeds (samaras) each year that disperse by wind to initiate new colonies. ToH also

serves as a preferred host for spotted lanternfly (Lycorma delicatula), a sap-

sucking invasive Asian planthopper that has been expanding its range into New

England, threatening wine grapes, fruit orchards, timber trees and other

economically important crops.

The preferred herbicide for ToH is triclopyr triethylamine salt (aka “triclopyr

amine,” brand name Garlon 3) which can be purchased as a concentrated solution

where it comprises 8% to 44% of total ingredients. Triclopyr is selectively toxic to

dicots (woody and most broadleaf plants) at concentrations that do not harm

monocots (grasses and related plants) and is safe for people and animals. Read the

product labels carefully to ascertain that triclopyr is the ONLY active herbicidal

ingredient and that the concentration is suitable for use on ToH – some ready-to-

use products are too dilute. Peter uses 44% solution without dilution for ToH trunk

treatment.  Concentrated solutions can be purchased online;

When to control ToH? Treatment is most effective once ToH trees have fully

leafed out in late spring until they begin to go dormant (foliage color change) in

mid-fall. In southern New England, this is typically late June through mid-October.

Within this seasonal window, earlier treatment (before July 1), especially of female

trees, can reduce or prevent seed production.