Arboriculture & Urban Forestry 33(1): January 2007 13 cern. For example, a number of microinjection labels allow or recommend repeated annual treatments. We believe injec- tions should be applied when indicated; monitoring is a criti- cal component in that decision-making process. Increasing the application interval to beyond an annual treatment, if possible, is a clear advantage. Wound response to stem injection is dependent on a num- ber of factors, including the tree species, the time of year, the method of injection, and the chemical formulation. The pat- tern of Compartmentalization of Decay in Trees (CODIT) (Shigo 1977, 1979) responses are similar in hardwoods and conifers; however, there are qualitative differences, because their anatomy and physiology are quite distinct. It has been our observation that eastern hemlock is less susceptible to injection wound infections compared with the ring porous hardwoods (e.g., American elm [Ulmus Americana] is highly susceptible to bacterial wetwood infection). Wound closure, on the other hand, occurs at a slower rate in hemlock than in American elm. This is related to tree vigor and species (Neely 1988). The time of year may influence wound response. Wound closure is dependent on growth and differentiation of callus tissue (Shigo 1989) and is limited by winter dormancy. In beech and oak, wound closure was reduced when injuries were made in December and February compared with wounds made in April or October (Dujesiefken et al. 2005). Hudler and Jensen-Tracy (2002), however, reported no sig- nificant differences in wounds inflicted mid-June or early November in eastern white pine (Pinus strobus). These data suggest that spring or fall injection wounds are less injurious than those applied during winter dormancy. Even so, the size (width × depth) and frequency of wounds also play a role in tree response to wounding. Systemic distribution of trunk injected chemicals into the canopy of conifers requires multiple injections sites (Larson et al. 1994). Recommendations for injection into hardwood trees follow this same pattern of distributing the application sites around the bole of the tree. The number of injection sites, however, varies with the method from a high of 3.75 application sites per cm trunk diameter at breast height (dbh) (1.5 application sites/dbh in) for Macro-infusion applications (Rainbow Tree, Minneapolis, MN) to the J.J. Mauget Com- pany (Arcadia, CA) microinjection recommendation of cen- timeters dbh/5 (dbh in/2). The number of application sites and distribution of the injected chemical are directly related. The variation in the number recommended, in practice, is related to the volume and frequency of application. For example, high-volume Macro-infusion applications are made less fre- quently (i.e., once every 3 years) compared with very-low- volume microinjection applications, which may be repeated annually. Although movement of sap in the stem is generally upward (i.e., straight sectoral ascent), there is considerable variation in the path of water movement across species. Spiral ascent occurs in a number of species, including conifer xylem (Kozlowski and Winget 1963). Furthermore, conifers and dif- fuse porous hardwoods tend to use a larger proportion of sapwood than the ring porous hardwoods for water move- ment. In a study using dye to assess canopy distribution in black cherry (Prunus serotina), a diffuse porous hardwood, injection applications were made comparing centimeters dbh/5 (dbh in/2) to cm dbh/10 (dbh in/4) (Doccola and Mc- Comiskey, unpublished data). The mean distribution of dye in the tree canopies were 92% and 80%, respectively. We made the assumption that injections into hemlock will distribute at least as well as that observed in the dye study. In this study, we applied the centimeters dbh/10 formula, which is half the number of application sites used in microinjection applica- tions to limit the wounds made. The injection sites were located around the lower bole of the tree in tissues immedi- ately superior to the trunk flare. Tattar et al. (1998), Webb et al. (2003), and Doccola et al. (2002, 2003) have demonstrated that trunk-injected imidaclo- prid (1-[(6-chloro-3-pyridinyl) methyl]-N-nitro-2-imidazoli- dinimine), a nicotinoid insecticide, is effective for control of HWA. In these studies, the amount of active ingredient (A.I.) applied using IMICIDE (J.J. Mauget Company) was 0.06 gm A.I./cm dbh (0.15 g A.I./dbh in) for small- and large-diameter trees. In this study, treatments were applied in early to mid- October using IMA-jet insecticide (Arborjet, Inc., Woburn, MA), a 5% by weight liquid formulation of imidacloprid. The amount of A.I. administered using the IMA-jet was commen- surate with tree size class and ranged from 0.04 to 0.12 g A.I./cm dbh (0.1 to 0.3 g A.I./dbh in). The mean dosage applied was 0.08 g A.I./cm dbh, comparable to the IMICIDE dosage. The purpose of this study was to assess IMA-jet insecticide efficacy after each of two fall treatments against HWA (i.e., 1 × dose × 2 treatments) and whether these out- comes suggest increasing the dosage to extend the application interval to once every 2 years (i.e., 2 × dose × 1 treatment). The formulation was applied directly to the xylem through a shallow drill hole (Martin and Sydnor 1987; Tattar and Tattar 1999) and of sufficient depth (15 mm [0.6 in]) to minimize exposure of the secondary vascular tissues surrounding the application site to the formulation chemistry. The latter was an important consideration to minimize injury (i.e., from chemical phytotoxicity to the cambium and phloem tissue surrounding the injection site). The application of low pres- sure ensured that the entire dosage was delivered. The timing of treatment was based on two factors, which were tree uptake and insect susceptibility. Coniferous species are more difficult to inject than hardwoods (Sanchez-Zamora and Fernandez-Escobar 2004) as a result of their vascular anatomy and response to environmental conditions. In hem- lock, the rate of uptake is limited by tracheid diameter (Tyree and Ewers 1991; Lancashire and Ennos, 2002; Mayr et al. 2003). Xylem flow depends on evapotranspirational loss ©2007 International Society of Arboriculture
January 2007
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