208 Adrian Site, 2006–2009 Green ash street trees in Adrian, MI, between 14 and 28-years-old and from 15–65 cm dbh (mean dbh = 43 cm in 2008), were se- lected for this test. Test trees were located between the street and the sidewalk in five different neighborhoods. All of the green ash street trees in these neighborhoods were used in the study if they had at least a 15 cm dbh, appeared to be relatively healthy (less than 25% canopy thinning and dieback in September 2005), and were spaced at least 15 m apart. Tree trunks were measured and marked with a metal tag during the first week of September 2005. Study trees were located in low-maintenance lawns, and very few were irrigated. Each treatment was replicated 10 times with each replicate consisting of an individual tree. Four insecticide treat- ments and two control treatments were evaluated from June 2006 to July 2009. A description of each treatment follows, including the formulation, type of application, rate, and application date. (1) Emamectin benzoate was applied once at 10 ml/2.54 cm dbh (0.4 g ai) on June 22, 2006. Trunk injections were made as previously described in the East Lansing test. (2) Emamectin benzoate, trunk injected as described in treat- ment (1). The only difference among these two treat- ments is that branch samples were collected and scraped to count larvae for treatment (1) but not for treatment (2). Unlike the previous two studies sites, (3) Imidacloprid 75 WP, was applied as a basal drench at a rate of 1.42 g ai/2.54 cm dbh. Annual treatments consisted of the appropriate amount of imida- cloprid mixed in 5.7 l of water and poured around the base of the tree within 70 cm of the trunk on June 27, 2006, May 24, 2007, and June 3, 2008. (4) Imidacloprid 5% SL, formulated by Arbor- jet and Bayer, was trunk-injected using the Arborjet Tree IV sys- tem at a rate of 0.2 g ai/ 2.54 cm trunk dbh. The formulated insec- ticide was diluted 1:1 with water and put into a bottle pressurized to 3.16 kg/cm2 before being injected through four sites on the lower trunk of each test tree on June 22, 2006. In addition, trees in treatment (4) also received an imidacloprid basal drench at a rate of 1.42 g ai/2.54 cm dbh on June 6, 2007, and June 10, 2008. Trees in treatments (5) and (6) were left as untreated controls. Canopy thinning and dieback ratings were made for each tree in early July of each year as previously described. Upper branches from trees in three treatments were col- lected between October 15 and 19, 2007. The bark was re- moved and EAB larvae counted as previously described. RESULTS Results from all three locations indicate a single trunk injection treatment of ash trees up to 45 cm dbh in size, made in May or June with emamectin benzoate at 0.1–0.4 g ai/2.54 cm dbh con- sistently gives nearly 100% control of EAB larvae even under intense pressure from EAB. Control trees declined rapidly at test sites due to EAB infestation, going from canopy thinning ratings of 19% to 54% in one year at Troy, 15% to 58% in four years at East Lansing, and from 15% to 87% in three years at Adrian, while canopy thinning ratings for ash trees that were trunk-inject- ed with emamectin remained similar throughout the test period. The death and removal of some trees decreased the number of replications in the third and fourth year of this study at the East Lansing and Adrian sites. Two trees at the Troy site and one tree at each of the East Lansing and Adrian sites were prematurely removed by city arborists during the winter by mistake. The av- ©2010 International Society of Arboriculture Smitley et al.: Protection of Ash Trees with Emamectin Benzoate erage area of bark sampled per tree was 1067 cm2 from 691 cm2 to 3,741 cm2 , and ranged , depending on the size of the tree. Troy Site, 2005–2006 Green ash street trees in Troy were of a uniform size at the begin- ning of the test in June 2005 (29.2–30.5 ± 6.5 cm dbh) (Table 1). Initial tree health ratings as measured by canopy thinning were also similar, with no differences among treatments with the exception of trees receiving the highest rate of emamectin benzoate. Ash trees in that treatment started the test in June 2005 with a significantly higher level of canopy thinning (41.5 ± 26.0%) compared with control trees (19.0 ± 14.7%). This happened despite a random assignment of trees to treatments. All rates of emamectin benzoate (0.1–0.6 g ai/2.54 cm dbh) were extremely effective when applied as a trunk injection in late May 2005. No larvae were found in any of the branch samples (30 branch sections per treatment) collected in October 2005, despite evidence of a moderate level of EAB tunneling injury from the year before (11.2 old galleries/m2 2005 (59.2 live larvae/m2 ) and intense pressure from EAB in in control trees). Complete protection of ash trees from the trunk injections of emamectin at all tested rates in May 2005 was expressed the following summer (July 2006) in canopy thinning ratings that were as good or better than the ini- tial ratings in June 2005 (16.7%–34.3% canopy thinning). Mean- while, control trees declined rapidly in response to the extensive damage caused by 59.2 larvae/m2 , deteriorating to a mean rating of 59.2% canopy thinning and dieback in June 2006 (Table 1). East Lansing Site, 2005–2009 Trees in the East Lansing site were of similar in size (28–38 ± 10 cm dbh) as those evaluated in Troy, but trunk injection treat- ments were initiated at an earlier stage of EAB infestation, when trees were still in excellent health based on average rat- ings of 7% to 17% canopy thinning (Table 2). EAB density in- creased four-fold in control trees from autumn 2007 to autumn 2008, going from 6.9±9.4 to 28.7±21.5 larvae/m2 , respectively. In stark contrast, no larvae were found in branch samples col- lected from trees that were trunk injected with emamectin benzo- ate three years earlier at a rate of 0.4 g ai/2.54 cm in September 2005. The same trees continued looking healthy through August 2009, when they were rated as having 13.8 ± 14.1% canopy thinning, compared to a mean rating of 58.1 ± 33.2% for con- trol trees (Table 2). Emamectin trunk injections made in May 2007 at the 0.1 or 0.2 g ai/2.54 cm dbh rate also provided ex- cellent protection, with no EAB larvae being found in branches collected from treated trees in October 2007 or October 2008. Adrian Site, 2006–2009 Green ash street trees in all treatments were healthy at the be- ginning of the test in July 2006 (14.2%–16% canopy thinning, Table 3). Trees in the two control treatments remained healthy in 2007 (10.3%–12% canopy thinning), but declined rapidly in 2008 (58.3%–64 % canopy thinning and dieback) in response to intense pressure from EAB. Nearly all the ash trees in both control treatments were dead by July 2009 (84.6%–89.5% canopy thin- ning and dieback). During the same time period (2006–2009), trees that were trunk-injected with emamectin benzoate at 0.4 g ai/2.54 cm dbh in June 2006 remained healthy (Table 3). Trees
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