6 Doccola et al.: Tree Wound Responses to Trunk Injection Arboriculture & Urban Forestry 2011. 37(1): 6–12 Tree Wound Responses Following Systemic Insecticide Trunk Injection Treatments in Green Ash (Fraxinus pennsyl- vanica Marsh.) as Determined by Destructive Autopsy Joseph J. Doccola, David R. Smitley, Terrance W. Davis, John J. Aiken, and Peter M. Wild Abstract. Trunk injection of systemic insecticides or fungicides is an effective way to manage destructive insects or diseases of trees, but many arborists are still reluctant to inject trees because of the potential for infection by pathogens, structural damage, or adverse effects on tree health. The authors of the following study examined wound responses of green ash (Fraxinus pennsylvanica Marsh.) for two years fol- lowing trunk injection, by sectioning tree trunks to look for evidence of infection associated with injection sites, and by collecting data on annu- al radial growth and rate of closure around injection sites. All healthy trees successfully compartmentalized injection wounds without any signs of infection, decay, or structural damage. Wound closure was positively correlated with the tree health as measured by annual radial growth. Key Words. Canopy Dieback; Decline; Emerald Ash Borer; Stem Injection; Systemic Insecticide; Tree Health; Wound Closure; Woundwood. The recent discovery that trunk injections of emamectin ben- zoate will provide 2–4 years of complete protection from em- erald ash borer (EAB, Agrilus planipennis Fairmaire) has led to a dramatic increase in the number of trunk-injected trees in the Midwest United States (Smitley et al. 2010). With trunk injections becoming a standard practice for arborists, more in- formation is needed on the long-term injury (i.e., two or more years) caused by trunk injections (Smith 1988). The mechani- cal wound made during injection is generally small but it could provide an entry point for pathogens, and the injected product (active ingredient + formulation) or the pressure applied dur- ing the injection process may injure cambial tissues (Shigo et al. 1977). Unfortunately, most publications on trunk injections focus on efficacy of the injected pesticide and rarely include an evaluation of the injury caused by the injections or how quick- ly trees recover from the injury (Chaney 1986; Ellmore et al. 1988; Tattar and Tattar 1999; Sanchez-Zamora and Fernandez- Escobar 2004; Dujesiefken et al. 2005; Smith and Lewis 2005). Fraxinus trees are ring porous (Salisbury and Parke 1970; Esau 1977), with the early wood vessels being larger and more visible than late wood vessels which are too small to be seen with the naked eye. Fraxinus trees also have broad con- ducting sapwood compared with many other tree species, like Ulmus, and Quercus (Shigo 1991). Trees are highly compart- mented plants with each annual ring of radial growth forming a compartment (Shigo 1984). Trees have evolved a strategy of growing around traumatized tissue rather than expending en- ergy to repair wounds. The compartmentalization process may be divided into two stages: reaction zones set up at the time of trauma in existing wood and responses (i.e., growth) that occur after trauma (Smith 2006). After a tree is wounded, the lateral ©2011 International Society of Arboriculture cambium divides to form new tissue that grows over the injury. This tissue is called the barrier zone. Barrier zones resist the out- ward spread of decay. A model describing the biochemical and anatomical process of wound response in trees was developed by Shigo and Marx (1977). Individual trees may vary consider- ably in the strength of their response to same type of wound de- pending on genetics or tree health (Shigo 1999). In this study, the advancing wave of EAB was taken ad- vantage of (Haack et al. 2002; McCullough et al. 2003; Mc- Farlane and Meyer 2003; Cappaert et al. 2005; Herms et al. 2009), along with the subsequent decline and death of green ash street trees in East Lansing, Michigan, U.S., to see how green ash trees in various states of health responded to wounding caused by standard trunk injection treatments. MATERIALS AND METHODS The purpose of this study was to determine how healthy and com- promised green ash trees respond to wounds caused by standard trunk injection treatments. As EAB swept through East Lansing between 2005 and 2009, trees declined rapidly from an extremely heavy borer infestation (> 50 larvae/m2 ), resulting in the death of all unprotected trees by 2009, while trees receiving effective insecticide treatments remained healthy (Figure 1a; Figure 1b; Smitley et al. 2010). Because the city of East Lansing was in the process of removing all of their green ash street trees due to the devastation caused by EAB, the study authors were allowed to cut and examine trees before they were removed. In order to observe the response of healthy and weakened trees to wounds created by insecticide injection, two green ash trees were ran- domly selected from each of seven trunk-injection treatments
January 2011
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