Tree of Heaven - November 7, 2007
Jeff Schalau, Associate Agent, Agriculture & Natural Resources, Arizona Cooperative Extension, Yavapai County
Environmental pollution takes many forms. We are keenly aware of air and water pollution from sources such as cars, factories, sewage, and so on. More recently, we have been fighting biological pollution: living organisms that negatively impact ecosystems they are introduced into. Biological pollutants are invasive, non-native plants, animals, insects, and other living organisms that decrease our quality of life and cost billions of dollars to control (eradication is usually not a realistic goal). Some examples are the zebra mussel, emerald ash borer, Asian longhorn beetle, and a long list of plants we also call invasive or noxious weeds.
The tree of heaven (Ailanthus altissima) is an invasive tree that originated in China, was brought to Europe in 1751 and was brought to the United States in 1784. Tree of heaven is a fast-growing, deciduous tree that can reach a height of 40-50 feet. The leaves resemble walnut or pecan (compound pinnate) but are much larger (1-3 feet in length). The leaves and male flowers have an offensive odor. It produces abundant winged seeds which readily germinate. When cut or damaged, the tree vigorously resprouts from the roots making it fairly difficult to control.
Verde Valley residents have likely seen this tree. It is probably the most common woody plant in Jerome. From there, it has spread down the washes into Cottonwood and Clarkdale. Dead Horse Ranch State Park also has several stands of these trees. They have colonized ditch banks and new populations appear as the seed spreads. Tree of Heaven gained fame through A Tree Grows in Brooklyn, the novel by Betty Smith. In many eastern U.S. cities it grows in the mortar of brick walls and on flat rooftops.
Most people start out liking the tree of heaven. It grows with little water, tolerates alkaline soils, and it creates shade. Most trees of heaven begin to produce seed at about 10 years of age. Male or female flowers are usually produced on separate trees. So, the after the 10 year honeymoon period, seedlings begin to come up everywhere. In addition, if the tree is damaged or cut down, then it begins to sprout from the roots. The tree of heaven also produces allelopathic chemicals that preclude other plants from successfully growing nearby. Allelopathy is common among invasive species.
Tree of heaven can be controlled but it requires diligence and long-term monitoring for regrowth. Young seedlings may be pulled or dug up, preferably when soil is moist. Care must be taken to remove the entire plant including all roots and fragments, as these will almost certainly regrow. Root suckers appear similar to seedlings, but would be connected to a pre-existing lateral root, and would be nearly impossible to remove effectively.
The most effective method of ailanthus control seems to be through the use of herbicides, which may be applied as a foliar (to the leaves), basal bark, or cut stump. Keep in mind that it is relatively easy to kill the above ground portion of ailanthus trees, you need to kill or seriously damage the root system to prevent or limit stump sprouting and root suckering. Always be extremely careful with herbicide applications in the vicinity of valuable ornamental shrubs and trees and always follow label directions.
For seedlings and small plants, I recommend a foliar spray with Glyphosate during the summer. Remember that any desirable green plant or plant part will also be killed using this method. For control of larger plants, I recommend a cut stump application of triclopyr. These products are often sold as stump killer or brush killer and must be applied immediately after cutting. I prefer to apply it with a cheap paintbrush and I also wear disposable latex gloves. Research indicates that it is most effective at controlling root sprouts when applied during summer. However, you should strongly consider using it anytime you cut down a tree of heaven.
There are many tree species that are better choices than the tree of heaven. The University of Arizona Cooperative Extension has publications and information on suitable tree species for any situation. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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