Arboriculture & Urban Forestry 38(6): November 2012 Arboriculture & Urban Forestry 2012. 38(6): 255–257 255 Control of Red Elm Bark Weevil (Magdalis armicollis) in American Elm (Ulmus americana) by Trunk Injection of Azadirachtin Michael Booth and Mark Goettel Abstract. Trunk injection of azadirachtin into elm trees (Ulmus americana) using the Ecoject™ gence numbers of red elm bark weevil (Magdalis armicollis) was evaluated. Twelve mature trees were each injected with TreeAzin™ Microinjection System to reduce emer- in ear- ly August 2010 at a rate of 16 ml per 15.2 cm trunk circumference at breast height. The following year, weevil activity was monitored at weekly intervals for four weeks using sticky traps placed in the canopies. There was a significant reduction of 55%–60% in weevil activity in early sum- mer in the treated tree canopies as compared to the control, suggesting that this method may be an effective management tool for this pest. Key Words. American elm; Azadirachta indica; Ecoject™ ; Trunk Injection; Ulmus americana. Microinjection System; Magdalis armicollis; Neem; Red Elm Bark Weevil; Sticky Trap Sampling; TreeAzin™ Populations of mature American elms (Ulmus americana), a highly prized ornamental tree on the Great Plains, are in decline, thus increasing their perceived value and need for protection. The red elm bark weevil (REBW) (Magdalis armicollis) is becom- ing a serious pest of elms. REBW eggs are laid beneath the bark where larvae and pupae develop. Populations have a tendency to increase in years with warm summers (M. Booth unpublished ob- servations, 1986–2007) and may increase under drought stress (Saunders et al. 2004). The larvae cause damage by feeding and tunneling along the cambium/xylem interface, which inter- rupts vascular flow and causes dieback of twigs and branches. Because the insect develops beneath the bark, it is very difficult to control using conventional pesticide application methods. Conventional insect control methods, such as foliar spraying, drench application, banding, or paint-on applications (Doughty et al. 1992), and soil injection have been shown to be effective means of insect control in urban trees, though off-target movement of pesticides may pose risks to non-target organisms, humans, soil, and water. Trunk injection of insecticides targets the pests direct- ly within the trees and has been shown to be an effective means of controlling insect pests of trees and shrubs (Marion et al. 1990; Doccola et al. 2003; Booth and Johnson 2009). Previous tests by the Canadian Forest Service and at the Lethbridge Research Centre (Booth and Johnson 2009) showed potential effective- ness of acephate for control of REBW applied with the Ecoject™ Microinjection System, developed by BioForest Technologies Inc. (Sault Ste. Marie, Ontario, Canada). The Ecoject injection tool pressurizes small plastic vials that inject small amounts of insecticide into the tree through holes drilled into the tree. Azadirachtin, extracted from the neem tree (Azadirachta indica), is known to possess systemic activity against sev- eral defoliating and leaf-mining insects when injected into trees (Helson et al. 2007). It is registered in the United States as TreeAzin™ for use against the emerald ash borer and other foliar-feeding tree pests (EPA Reg. No 82996-1). Researchers evaluated trunk injection of azadirachtin into elm trees using the Ecoject Microinjection System as a means to reduce emer- gence numbers of the REBW at the Lethbridge Research Centre. METHODS AND MATERIALS Experimental Design The experimental units were 24 mature trees, part of a row plant- ing. These trees are on federally owned and managed property near Hwy #3, east of Lethbridge, Alberta, Canada. Twelve trees were treated, and 12 acted as controls. The experimental de- sign consisted of four treatment trees followed by four control trees followed by four treatment trees and so on, creating three treatment groups of four trees each and three control groups of four trees each. Trunk circumference at breast height of the 24 trees ranged between 109 cm to 218 cm (mean = 156 cm). Injection Treatment The target application rate was 16 ml of TreeAzin Systemic Insec- ticide (5% azadirachtin; BioForest Technologies, Sault Ste. Ma- rie, ON)/15 cm trunk circumference at breast height. Trees were measured and assigned a number of injectors based on tree size: two, 8 ml injectors per 15 cm of trunk circumference. The number of canisters used per tree ranged from 14 to 28. The canisters were pressurized using the Ecoject Microinjection System and inserted into 5.6 mm holes (2–8 ml canisters/hole) drilled near the base of the tree, 1.3–1.9 cm deep, to the cambium. The injector pressure ©2012 International Society of Arboriculture
November 2012
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