148 Booth and Johnson: Trunk Injection of Acephate on American Elms Arboriculture & Urban Forestry 2009. 35(3): 148–151 Pressurized-Canister Trunk Injection of Acephate, and Changes in Abundance of Red Elm Bark Weevil (Magdalis armicollis) on American Elm (Ulmus americana) Michael Booth and Dan Johnson Abstract. Portable pressurized injection vials (Ecoject System) were used in an experiment to assess injection of acephate into elm trees (Ulmus americana) as a means of reducing within-tree abundance of red elm bark weevil (REBW), Magdalis armi- collis. A total of 25 elm trees were treated, each paired with an untreated tree. A total of 400 pressurized canisters were used in the study. REBW population density, as indicated by sticky-paper trap catches, on treated and untreated trees did not differ significantly at the time of trunk injection. Two weeks after injection, the average REBW trap catch on the 25 untreated trees had increased, whereas the average trap catch on the 25 treated trees had decreased. The resulting average trap catch from the treated trees was significantly lower than that of the control trees. Although subsequent declines in REBW populations precluded a longer record of the effects of tree injection, the significant reductions apparent in the first two weeks following injection indicated the method was effective in reducing REBW abundance. The impact on REBW populations was detectable even though treated and untreated trees were contiguous, indicating that selective treatment of individual trees could be part of an effective operational treatment for REBW management. No phytotoxic effects were detected by spectrophotometric assessment of leaf chlorophyll. Key Words. Acephate; American elm; Canadian Prairies; Chlorophyll; Ecoject; Magdalis armicollis; Population Reduction; Red Elm Bark Weevil; Spectrophotometric; Sticky Trap Sampling; Trunk Injections; Ulmus americana; . Elm trees (Ulmus americana) are highly valued on the Canadian Prairies and Northern Great Plains, for reasons of aesthetics, lon- gevity, and ecological services. The mature elm population is in decline, accentuating perceived value and need for protection. Red elm bark weevil (REBW), Magdalis armicollis, is a poten- tially serious pest of elm trees in grassland and parkland regions of western Canada and the United States. REBW eggs are laid be- neath the bark, and larval and pupal stages develop in situ. Adults emerge from bark the following year, and feed on growing leaves, resulting in typical shothole defoliation. Populations of REBW tend to increase in years with warm summers (M. Booth, unpub- lished observations, 1986-2007), and may also increase under drought stress (Saunders et al. 2004). Risk of REBW damage to elms is not a new problem in North America. Tucker (1907) de- scribed elm trees that were killed by the larvae boring into branch- es and trunks, and concluded that destruction of the afflicted trees was the only way to prevent more extensive infestations; this giv- en the lack of control agents available in the early 20th Century. More recently, foliar spray application, drench applica- tion, banding or paint-on applications (Doughty et al. 1992), and soil injection of insecticides have shown to be effective control methods for other pests of urban trees. Unintended off- target movement of pesticides may pose potential risks to non- target organisms (including natural enemies of pests), soil, and water. Trunk injection of insecticides has shown to be an ef- fective method of controlling insect pests of trees and shrubs (Gill et al. 1999; Tipping and Center 2002; Young 2002; Doc- coloa et al. 2003). Injection has potential for limiting other boring or bark-infesting insect pests of ornamental trees, such ©2009 International Society of Arboriculture as elm bark beetle, emerald ash borer, lilac borer, western ash bark beetle, and other pests that feed within plant tissue. General monitoring of REBW infestations on Govern- ment of Canada property was conducted during 1986-2006 (M. Booth, unpublished observations at Lethbridge Research Center). During May to August 2006, an experiment was con- ducted to evaluate the effects of trunk injection of pressur- ized liquid formulation of acephate (Orthene) on abundance of red elm bark weevil in American elm in Alberta, Canada. Previous tests by the Canadian Forest Service indicated po- tential effectiveness of the Ecoject injection system devel- oped by BioForest Technologies Inc. (Sault Ste. Marie, ON, Canada). The Ecoject injection tool pressurizes small plas- tic vials, which inject small quantities of insecticide into the tree when they are inserted into holes drilled into the trunk. MATERIALS AND METHODS Experimental Design Randomization and Replication The experimental units in the trial consisted of 50 mature Ameri- can elm trees. Treatment was randomly assigned to one tree in each of 25 contiguous pairs, so that each of the 25 randomized blocks of the experiment consisted of two mature American elm trees, standing together on the same side of a paved lane. The lane is on federally owned and managed research property near Highway 3, east of Lethbridge, Alberta, Canada. One reason for using a paired-tree randomized block design was to deter-
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