Tree Injection as an Alternative Method of Insecticide Application

Injection directly into the conductive tissues of trees was a method first investigated systematically by Leonardo da Vinci, but some of the most early tree injection experiments were not recorded until early in the 20th century (Roach, 1939, May, 1941, Costonis, 1981). Dutch elm disease, a destructive vascular wilt disease of elm renewed interest in tree injection in the 1970s (Jones and Gregory, 1971; McWain and Gregory, 1971; Jones et al., 1973; Gregory et al., 1973; Gregory and Jones, 1975; Shigo and Campana, 1979; Kielbaso et al. 1979; Shigo et al., 1980), when more common fungicide applications proved ineffective. During this time, several injection methods, including trunk infusion (Schreiber 1969), and pressurized trunk injections (Filer 1973; Helburg et al. 1973; Reil and Beutel 1976, Sachs et al., 1977; Kondo, 1978, Darvas et al., 1984, Navarro et al., 1992), were developed. Tree injection was also used for treatment of other tree pathogens (Guest et al., 1994; FernándezEscobar et al.1994, 1999), insects, and physiological disorders (i.e., interveinal chlorosis) in the EU (Fernández-Escobar et al. 1993). Interest in tree injection technologies (McClure, 1992, Doccola et al., 2007; Smitley et al., 2010) in the US has also increased, with the introduction of several tree killing insects such as hemlock woolly adelgid (Adelges tsugae), Asian longhorned beetle (Anoplophora glabripennis) and emerald ash borer (Agrilus planipennis). In addition to new injection technology, formulations are being designed for injecting into trees that improve plant safety and reduce application time. Examples of the new technologies are the TREE I.V. micro-infusion system and Air/Hydraulic micro-injector (Arborjet, Inc. Woburn, MA, USA) and the Eco-ject® Microinjection System (Bioforest Technologies, Canada). Today, tree injection is an alternative method of chemical application with certain advantages: (1) efficient use of chemicals, (2) reduced potential environmental exposure, and (3) useful when soil and foliar applications are either ineffective or difficult to apply (Stipes, 1988; Sanchez-Zamora and Fernandez-Escobar, 2004). Tree injection into roots, trunks or limbs requires wounding of the tree, which has implications to the tree’s health. The question often asked is, does the benefit gained by tree injection outweigh the risk of the wound caused by treatment? This question of cost-benefit is certainly valid. However, this concern must also be weighed against environmental (and off target) exposures when trees are sprayed or insecticides are applied to the soil. An underlying assumption is that the value of the tree and its treatment is greater than sustaining tree loss. Key factors weigh in to wound responses in trees that likewise demand consideration. These include (1) the tree species, (2) tree health, (3) the attributes of the