Arboriculture & Urban Forestry 37(1): January 2011 that were part of a larger study. The seven insecticide treatments were chosen to represent a range of efficacy based on the active ingredient and year the insecticide was injected in relationship to the borer infestation (Smitley et al. 2010; Table 1). Trees that appeared to have a flat or sunken area of the lower trunk due to a previous injury or infection were excluded from this study. Selected trees ranged from 21.5 to 36.3 cm dbh (mean = 27.6 cm) and were located between the street and the sidewalk in one of seven different neighborhoods. All trees were healthy at the beginning of the study (< 25% canopy thinning). Annual canopy thinning and dieback ratings were made in July of each year by comparing the canopy of each tree with photographs in various stages of decline from 0% (healthy) to 100% (dead) in 10% increments (Smitley et al. 2008). Each tree was rated by two or three individuals and averaged across observations to obtain an annual rating. Insecticides placed into green ash trees by trunk injection or by implantation were: emamectin benzoate (TREE-äge, 0.04 g/g ME, Syngenta Crop Protection, Greensboro, NC, U.S.), imidacloprid (0.05 g/g SL, IMA-jet, Arborjet, Inc., Woburn, MA, U.S.), imidacloprid (0.20 g/g SL, MERIT Tree Injec- tion, Bayer Crop Science, Clayton, NC, U.S.), and acephate (ACECAP 97S, 0.97 g/g, Creative Sales, Fremont, NE, U.S.). Products were injected per label instructions as diluted with water or neat (nondiluted). Treatments were applied using no pressure (i.e., implants only), low pressure (310 kPa) micro- 7 infusion™, or high pressure (1379 kPa) micro-injections. Drill holes varied in diameter, depth, frequency and location on the stem based on the specific method of application used. For the ACECAP 97 (acephate) treatment a 9 mm diam- eter drill bit was used to drill 3.2 cm deep into the sapwood. Holes were drilled 10 cm apart on the stem spiraling up and around the trunk from the base of the tree, until the correct number of holes (i.e., seven or eight per tree) was drilled ac- cording to the label. Two trees were treated with acephate implants on May 16, 2006, at a rate of 0.60 g AI/2.54 cm. The four trees trunk-injected with TREE-äge (emamectin benzoate), were injected by low pressure micro-infusion™ . These injections were made by drilling four injection ports with a 7 mm diameter drill bit. Holes were drilled perpendicular to the trunk and were located 15 to 20 cm apart on the trunk circumfer- ence at a height of 20–40 cm above the ground. Plastic septums (Arborjet #3 Arborplug) were tapped into the drilled holes and the ports connected with plastic tubing to a single pressurized 310 kPa bottle containing TREE-äge diluted 1:1 with water. The TREE-äge solution was injected at a rate of 0.4 g AI/2.54 cm DBH on September 27, 2005. No additional treatments were made to two of the four trees for the duration of the test. The two remaining trees were re-treated on May 21, 2008 with TREE- äge using the same apparatus and rate but drill holes were larger (9 mm diameter). Repeat injections were staggered from the original injection sites a minimum of 5 cm whenever possible. Figure 1. Green ash street trees in East Lansing, Michigan in August 2009 just before trees were felled for this study: a) tree receiving TREE-äge trunk injections in fall 2005; b) control tree. ©2011 International Society of Arboriculture
January 2011
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