Arboriculture & Urban Forestry 42(6): November 2016 response to macroinjections remains relatively unevaluated. Understanding effects of macroin- jections on ash trees is especially important given the increasingly wide use of emamectin benzoate (EB) and other trunk-injected systemic products for control of EAB and other pests. The objectives of the current study were to determine if 1) trunk injections of the TREE-äge product created exter- nal bark cracks or necrosis in green ash or white ash trees, 2) discoloration in xylem was indica- tive of injury to xylem, and 3) whether injury or response of trees to injections varied between ash species, application rates, or frequency of injections. METHODS Two-Year Study Researchers evaluated injection sites on 46 ash trees growing in four locations in Ionia, Gen- esee, and Clinton Counties in central Michigan. The 22 green ash trees ranged in size from 10.7 to 29.2 cm DBH (mean ± SE = 18.1 ± 1.10 cm), and the 24 white ash trees ranged from 10.7 to 22.6 cm DBH (mean = 17.5 ± 0.61 cm). All trees were injected with TREE-äge (4.0%, ArborJet, Inc., Woburn, Massachusetts, U.S.) between 21 and 23 May 2008. A total of 24 trees were treated using the lowest label application rate (EB-low) (0.1 g a.i. per 2.5 cm DBH) applied with a QUIK- jet system (Arborjet, Inc. Woburn, Massachu- setts, U.S.). The other 22 trees were treated with a medium-high rate (EB-high) (0.4 g a.i. per 2.5 cm DBH) plus an equal amount of water applied with a TREE IV Micro-Infusion® system (Ar- borjet, Inc. Woburn, Massachusetts, U.S.). The number of injection sites was based on individual tree DBH (one injection site for every 15.2 cm DBH). Injection sites were evenly spaced around the base of the trunk, avoiding areas with dead tissue or previous wounds. The insecticide was applied using a 0.95 cm drill bit, then inserting plastic plugs (Arborplugs #4, 0.95 cm, Arborjet, Inc., Woburn, Massachusetts, U.S.) with a set tool and plastic mallet, according to label directions. From 02–04 June 2009, 22 trees, including 11 EB-high and 11 EB-low trees, were re-treated at the same rates and with the same methods as in 2008. Injection sites were approximately 5 cm above and offset from 2008 injections, according 391 to label directions. The remaining 24 trees, includ- ing 11 EB-high and 13 EB-low trees, were not re-treated in 2009. All trees were felled between October and December 2009. Aſter felling, the basal 50 cm of each bole was returned to the lab- oratory and cut into 5 cm thick cross sections. Cross sections were reassembled aſter cutting, and reference points were established to ensure proper orientation throughout the experiment. A total of 239 injection sites were examined on 46 trees. Six injection sites had no associated discoloration (four sites on four 2008 and 2009 EB-high trees, one site on a 2008 EB-high tree, and one site on a 2008 EB-low tree) because the applicator determined plastic plugs were set improperly and no insecticide was injected. These six injection sites were excluded from fur- ther analyses. Of the 233 injection sites exam- ined, 50 were from the 11 EB-high trees treated in 2008 only, 77 were from the 11 EB-high trees treated in both 2008 and 2009, 42 were from the 13 EB-low trees treated in 2008, and 64 were from the 11 EB-low trees treated in 2008 and 2009. Researchers visually examined each cross sec- tion and recorded the presence of secondary wounds, including external bark cracks, internal xylem necrosis, and any evidence of pathogen infection (e.g., soft tissue, discoloration) around each injection site (Figure 1). The presence of “new xylem tissue” was also recorded, a term used to refer to latewood produced later in the sum- mer following the injections, and when appropri- ate, the earlywood and latewood produced the year after injections (Figure 2) (Dickison 2000). Researchers also assessed discoloration height, length, and width, and calculated the area of discoloration around each injection site. Dis- coloration height (cm) was the vertical distance discoloration persisted above and below the basal cross sections. Discoloration length (mm) was the longest distance between the outer edge of discoloration (near the bark) and the inner edge (near the heartwood) (Figure 1). Discoloration width (mm) was the widest distance between left and right edges of the discoloration associ- ated with a single site (Figure 1). Discoloration area (cm2 ) was calculated using the formula for an ellipse: Area = π(length ÷ 2) × (width ÷ 2). ©2016 International Society of Arboriculture
November 2016
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