Arboriculture & Urban Forestry 33(1): January 2007 Arboriculture & Urban Forestry 2007. 33(1):55–63. 55 Control of Ailanthus altissima Using Stem Herbicide Application Techniques Joseph M. DiTomaso and Guy B. Kyser Abstract. Three herbicides were tested using four stem application techniques for control of both single trunks and clumps of tree-of-heaven [Ailanthus altissima (Miller) Swingle]. Imazapyr, triclopyr, and glyphosate were applied using cut stump, stump injection, and stem injection techniques. Imazapyr and triclopyr were also applied as a basal bark treatment. Treatments were compared against manual cutting and untreated controls. Untreated cut stems did not provide control of tree-of-heaven. Cut stump treatment with imazapyr and triclopyr (20% v/v in oil) resulted in more than 90% reduction in both vigor ratings and resprouting of single stems and clumps. In contrast, stump injection applications were ineffective with all herbicides. For stem injection treatments, undiluted imazapyr gave the best results (>95% canopy reduction), but glyphosate also provided excellent control (92% canopy reduction). Removing stems 4, 8, or 12 months after treatment did not impact the level of control with imazapic. Imazapic at half the standard rate also gave good control of multistemmed clumps. Basal bark treatments with imazapyr or triclopyr (20% v/v in oil) gave equally good results, providing nearly complete control. Triclopyr is less selective than imazapyr and thus offers a better option when desirable vegetation surrounds the stems. These results provide several effective options for the control of tree-of-heaven in both urban and riparian sites. Key Words. Ailanthus; basal bark; cut stump; glyphosate; herbicide control; imazapyr; invasive tree; manual cutting; riparian; stem injection; stump injection; tree-of-heaven; triclopyr. Tree-of-heaven [Ailanthus altissima (Miller) Swingle] is na- tive to eastern Asia. In 1751, it was brought to England (Feret 1985) and in 1784 was introduced to Philadelphia in the United States as an ornamental (Wyman 1951). It was again imported to Long Island in 1790 and its use as a cultivated plant quickly expanded into the eastern and midwestern United States (Feret 1985). It has been postulated that tree-of-heaven was first intro- duced to California and other western states as an ornamental in the 1800s with the Chinese who immigrated during the Gold Rush (McClintock 1981) or were used to build the western rail systems (Feret 1985). By the early 1900s, tree- of-heaven declined in popularity owing to a number of fac- tors. It resprouts prolifically from both shallow spreading roots and cut stumps, so that once established, it is difficult to remove. In addition, the foliage produces an unpleasant odor, which is associated with headaches and nausea. The leaves or leaf leachates can also cause dermatitis with vesicular erup- tions (Burrows and Tyrl 2001), and the pollen is a known allergen (Blumstein 1943). Despite decreased popularity, tree-of-heaven escaped cul- tivation and expanded its range in most of the United States (Merriam 2003; DiTomaso and Healy 2006). It is currently established in urban waste areas, old dwellings and mining settlements, roadsides, utility rights-of-way, pastures, and disturbed forest sites (Burch and Zedaker 2003). In the east- ern United States, tree-of-heaven has also established in for- ests where it has been shown to create dense stands and outcompete native woody species (Knapp and Canham 2000; Call and Nilsen 2005). In California, it is a highly invasive tree in riparian areas as well as grassland and woodland sites (Hunter 2000, Kelly 2001). It can survive from sea level to at least 1585 m (5,231 ft) under a broad range of soil conditions but generally grows best in areas where soil moisture is not limiting (Feret 1985). Tree-of-heaven is a shade-intolerant species that grows rapidly and quickly establishes in the gaps of forest or ripar- ian areas (Knapp and Canham 2000). Although seedlings cannot survive under a dense canopy, root sprouts grow slowly and survive for years under an intact canopy (Kowarik 1995). Once released by the development of a gap, these clonal ramets can rapidly establish. When exposed to light, new shoots can grow up to 1.8m(5.94 ft) in length in a single season and can eventually reach heights of nearly 18 m (59.4 ft) (Feret 1985). Although a number of factors contribute to the competitive ability of tree-of-heaven, it may outcompete other species through the production of quassinoids that act as allelochemi- cals (Heisey 1990; Lawrence et al. 1991; Heisey 1996; Hei- sey and Heisey 2003). The most active of these compounds is ©2007 International Society of Arboriculture
January 2007
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