If you start looking around Clackamas County, it won’t take you long to find the invasive tree-of-heaven (Ailanthus altissima). This state-listed noxious weed is increasingly more common in many of our urban areas where it flourishes. Tree-of-heaven seems right at home in alleys, roadsides, railways, vacant lots, that crack in the sidewalk. Very large trees […]
tree-of-heaven, stinking sumac, stinking quassia, copal-tree, Chinese sumac, varnish tree
Ailanthus altissima
Tree-of-heaven is an introduced deciduous tree species that can grow up to 80 feet tall and six feet in diameter. It has large pinnately compound leaves. Plants are dioecious (male or female) with females producing copious seeds each season.
It is seen in diverse locations across our region but is most commonly seen growing in urban areas, where it was once intentionally introduced. Vast numbers of seedlings, saplings, and suckering plants can be seen growing near larger parent trees. The bark on young trees is smooth and green. As it ages, the bark turns gray and develops shallow, diamond-shaped fissures. The green to brown branches grow alternately on the tree and have a pithy, brown center. The branches are also pock-marked with a V-shaped or heart-shaped leaf scars.
Leaves are pinnately compound, meaning they have leaflets attached on each side of a central stem. Leaflets have mostly smooth edges with one to two protruding bumps at the base called glandular teeth. When crushed, the leaves can have a rancid peanut butter-like odor.
Male and female flowers form in terminal clusters on separate trees. Flower clusters may be up to 12 inches wide and are largest on male trees. Tiny individual flowers are light green to pale.
In late summer through autumn, tree-of-heaven produces large clusters of papery winged fruit known as samaras. Each fruit contains a single central seed. The samaras vary from greenish-yellow to red-brown and are often vibrantly colored in the fall.
Tree-of-heaven produces a long taproot and suckers freely when cut, making it difficult to control. Creeping roots may extend outward up to 50 feet in all directions.
Tree-of-heaven can be easily confused with other trees that have compound leaves with many leaflets, such as sumac or walnut. The leaf edges of the look-alikes typically have teeth or serrations, while those of tree-of-heaven are smooth. Tree-of-heaven has characteristic glandular teeth and the base of the leaves which help to distinguish it from look-a-likes.
This weed reproduces both by seed and vegetatively through sprouting roots. New shoots can sprout as far as 50 feet away from the parent tree. One tree can produce over 300,000 seeds annually, which are then dispersed by water, wind, and birds. Cut stems can form roots when left on moist ground.
Tree-of-heaven grows in a variety of habitats and is commonly found in disturbed areas along forest edges, roadsides, fence rows, urban parks, old fields, and railroad embankments. It is tolerant of full sun to part shade, many types of pollution, and poor soil conditions. It can grow in many harsh environments, including pavement cracks and building foundations!
Tree of heaven has been known to cause skin irritations or allergies in some people. Additionally, there have been rare reports of myocarditis (inflammation of the heart muscle) from exposure to sap through broken skin. People who work around the tree should wear personal protective equipment, including eyewear and gloves.
The first documented appearance of tree-of-heaven in Oregon can be found in local herbaria dating back in 1904, in Wasco County. The plant is native to China and was commonly introduced as an ornamental plant before escaping cultivation. It is believed to have been introduced sometime between 1875 and 1899.
Tree-of-heaven is found throughout much of Clackamas County. As a common weed, this is not a species that is actively surveyed. The mapped distributions do not represent the full extent of tree-of-heaven in Clackamas County.
The management of invasive weeds is best served through a process known as Integrated Pest Management (IPM). IPM is a weed management methodology that utilizes:
An IPM based strategy ensures the maximum effectiveness of treatment measures. IPM strategies typically use more than one management method to target one or more susceptible life stages. It is adaptive to site conditions in the field and to the response of a plant to management. The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan. The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a weed particular infestation.
Manual removal of tree-of-heaven can be an effective control option for seedlings and small samplings, but it is labor-intensive. Plants can be pulled when the soil is moist to ease the removal of the roots and to put less strain on the worker. All plants and roots need to be removed to prevent regrowth. A weed wrench, shovel, or hoe can be used to assist with root removal. Sites should be monitored for regrowth regularly to ensure complete control. Once plants become too large and develop a strong root system other control methods will be required.
While manual removal can be an effective treatment, it can cause heavy soil disturbances on site. Soil disturbance can bring tree-of-heaven seeds to the surface creating a new generation of growth. Minimize soil disturbance and re-vegetate disturbed areas to prevent further infestations.
Cutting tree-of-heaven is not effective and should be avoided. Cutting can stimulate the suckering of new shoots, especially in larger specimens. A hack-and-squirt, or similar herbicide treatment (see below) will need to be utilized to control suckering and continued growth following cutting.
The cutting of a large tree-of-heaven is ineffective on its own. Cut trees will lead to significant resprouting from roots. As a result, cutting and removal of well-established trees should only be incorporated after trees have received a prescribed herbicide treatment. Chain saws are typically used to fell dead or dying tree-of-heaven following herbicide treatments. Large specimens can pose a risk to people and property. Whenever you are working in sensitive areas, you should coordinate removal activities with a licensed arborist.
Tree-of-heaven does not compete well in heavily shaded areas. Competitive plantings can help to minimize the impacts of tree-of-heave and prevent establishment.
Chemical control is an effective tool to control large trees and dense infestations. Tree-of-heaven is susceptible to several systemic herbicides. Plants should be treated using foliar treatments, basal bark, hack, and squirt, or cut stump methods. Chemical control options are frequently used in conjunction with other control practices within a broader IPM framework.
Product Names: Accord, Aquamaster, Rodeo, Roundup, and various others (glyphosate) + Garlon 3a, Element 3a, Vastlan (Triclopyr)
Rate:
Foliar treat: use glyphosate at 3 qts/acre with triclopyr at 1.5 – 2qts/ac, plus a non-ionic surfactant.
Time: Foliar applications should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. This mixture is not selective and will harm grasses and other desirable vegetation. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control.
Product Names: Accord, Aquamaster, Rodeo, Roundup, XRT II, and various others
Rate:
Foliar treat: use 2.0% to 4.0% v/v solutions, plus 0.5% v/v non-ionic surfactant.
Hack and Squirt: apply 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Glyphosate is not selective and will harm grasses and other desirable vegetation. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Cut stems horizontally at or near ground level and immediately apply herbicide.
Product Names: Garlon 4 (triclopyr ester), Garlon 3A, Element 3A (triclopyr amine), Pathfinder II, Vastlan
Rate:
Foliar treat: 1.0% to 2.0% v/v solution, plus 0.5% v/v non-ionic surfactant.
Hack and Squirt: make 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Basal Bark: use 20%-30% v/v in 70%-80% oil carrier.
Cut Stump: use 20%-25% v/v solution.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Triclopyr is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Triclopyr ester formulations may volatilize under warm temperatures. Expect root suckering following cut stump treatments.
Product Names: Vanquish, Banvel
Rate:
Foliar treat:5.0% v/v solution, plus 0.5% v/v non-ionic surfactant.
Cut Stump: use 25%-50% v/v solution.
Time: Foliar application and cut stump treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Dicamba is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Dicamba formulations volatilize under warm temperatures. Expect root suckering following cut stump treatments.
Product Names: Capstone
Rate:
Foliar treat: 1.0% to 1.5% v/v solution, plus 0.5% v/v non-ionic surfactant.
Time: Foliar application treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Triclopyr + aminopyralid is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Formulations may volatilize under warm temperatures.
Product Names: Arsenal, Habitat, Stalker, Chopper, Polaris
Rate:
Foliar treat: 1 to 2% v/v solution plus 0.25 to 0.5% surfactant v/v
Cut stump: 20% v/v solution in water plus 80% oil or water carrier, depending on product used.
Hack and Squirt: make 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Basal Bark: use 20% in 80% oil carrier.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Imazapyr is a soil residual herbicide and may result in bare ground around plants after treatment.
Product Names: Escort
Rate:
Foliar treat: 2 oz per acre
Time: Foliar application treatments should be carried out in summer or early fall.
Comments: Can be tank-mixed with glyphosate or triclopyr
There are no approved biological agents available at this time. Current research is underway to determine the suitability of three fungal pathogens and two insects to help control tree-of-heaven.
Small tree-of-heaven plants that have not gone to seed can be disposed of in yard debris containers. Tree-of-heaven plants that have gone to seed should be kept on-site to minimize the spread of the seeds, or bagged before disposal. Larger trees should be chipped or left on-site following removal, when possible. In some areas plant debris can be burned on-site with appropriate safety measures and permits. You should check with your local Fire District or the Oregon Department of Forestry for rules and recommendations.
Diligence is the most important aspect of controlling tree-of-heaven. Removal of new tree-of-heaven plants and monitoring and retreatment of suckering roots may occur years following treatment. So follow-up is required. Work with neighbors to target nearby seeding trees.
