210 Smitley et al.: Protection of Ash Trees with Emamectin Benzoate Table 3. Adrian, Michigan: emerald ash borer larval density in green ash street trees and canopy thinning ratings of the same trees for 3–4 years after a single trunk injection of emamectin benzoate on June 22, 2006. Data are means ± SD. Each treatment has 10 replications unless shown under the mean ± SD as (n). Treatment Emamectin trunk injection 0.4 g ai/inch dbh Emamectin trunk injection 0.4 g ai/inch dbh Imidacloprid trunk injection + soil imidacloprid Soil imidacloprid Control 1 Control 2 June 2007 38.4 ± 9.8 A 14.9 ± 3.6 A 12.0 ± 4.9 A - + June 2007, 2008 13.5 ± 12.0 A - 23.9 ± 10.1 A June 2006 43.1 ± 12.2A 16.0 ± 5.0 A 11.6 ± 6.5 A 2.4 ± 7.1 A 13.0 ± 12.7 A (9) 0 ± 0 A (9) 20.0 ± 8.0 A Treatment 2008 dbh dates (cm) June 2006 45.0 ± 8.1 Az 2006 canopy 2007 canopy 2007 larvae 2008 canopy 2008 larvae 2009 canopy thinning (%) thinning (%) per m2 14.4 ± 3.1 A 11.1 ± 6.0 A - thinning (%) per m2 12.3 ± 10.4 A - thinning (%) 7.2 ± 6.7 A June 2006, 39.6 ± 15.0 A 14.2 ± 5.7 A 8.4 ± 4.0 A 3.6 ± 6.8 A 33.0 ± 25.8 AB 5.7 ± 5.6 2007, 2008 AB (4) - - 43.4 ± 16.9 A - 12.0 ± 15.1 A - 58.3 ± 26.5 BC 23.6 ± 39.4 89.5 ± 13.4 B B (8) 44.7 ± 11.2 A 15.6 ± 5.4 A 10.3 ± 7.0 A 6.2 ± 6.6 A 64.0 ± 29.3 C 27.7 ± 28.9 84.6 ± 12.0 B B (7) z Means followed by the same letter are not significantly different at P = 0.05, by the Tukey-Kramer test. Ash trees receiving an annual basal drench of imidacloprid or a combination of an imidacloprid basal drench and an imidacloprid trunk injection also appeared healthy as determined by canopy thinning ratings at the end of the Adrian test, but significantly more EAB larvae (5.7 per m2 compared with emamectin benzoate-treated trees (0.0 per m2 ) were found in imidacloprid-treated trees ). Protection of ash trees for 2–4 years following a single in- secticide treatment completely changes the prognosis for ash street trees and shade trees in North America after invasion of emerald ash border. Up until this time, insecticide treatment was reserved for only the most valuable trees because of the high cost of making frequent trunk injections. The multiple-year protection documented in this study reduces the projected cost of saving ash trees by at least 50%, bringing treatments well within the range of many homeowners and some cities or other municipali- ties. For example, one can compare the cost of hiring an arbor- ist to treat a 31.4 cm dbh ash tree with annual trunk injections of IMA-jet (imidacloprid) at the 8 ml/2.54 cm dbh rate, to the cost of hiring the same arborist to treat every other year or every fourth year with TREE-äge (emamectin benzoate) at the 0.4 g ai/2.54 cm dbh rate. At the time of this writing the cost of the imidacloprid insecticide to the arborist is USD $23.92 per year, the cost of the emamectin benzoate insecticide is $26.13 per year when treating every third year, and $17.42 when treating every fourth year. Labor costs vary depending on the arborist, the number and size of trees being treated, and the location of the property. If one adds a labor charge of $50.00 per treatment- visit for the 31.4 cm dbh tree, then the total average cost per year over a three-year period would be $73.92/year for annual imi- dacloprid trunk injections, $51.13/year for emamectin benzoate injections made every third year, and $34.09/year for emamectin benzoate injections made every fourth year. This brings the cost of trunk injections into a much more practical range for home- owners, especially when weighed against the cost of tree removal which may be more than $1,500 for a large tree (62.8 cm dbh). ©2010 International Society of Arboriculture Data from Troy, East Lansing, and Adrian, MI, indicate most of the ash trees in cities along the leading edge of the contiguous EAB invasion front will perish within five years of when the first trees are found to die from EAB. This was cer- tainly true for Troy, MI, and much of the Detroit Metropolitan area where the first ash trees began to die in 2004. By 2009 all of the ash trees were dead except ones that were protected with insecticide treatments or where young trees have sprouted from the stumps of dead ones. Sprouting ash trees and the ger- mination of ash seed will guarantee the survival of EAB, but populations will be much smaller after the initial five to eight- year period when unprotected ash trees perish. This means the remaining ash trees will be easier to protect with insecticides. Acknowledgments. We appreciate the assistance of Terrance Davis for supervising the field research, and the Cities of Troy, East Lansing, and Adrian, for assisting with branch sampling. This research was partially supported by Arborjet, Inc., Syngenta Crop Science, and the Michigan Agricultural Experiment Station. LITERATURE CITED Bray, A.M., L.S. Bauer, R.A. Haack, T. Poland, and J.J. Smith. 2007. Invasion Genetics of Emerald Ash Borer (Agrilus planipennis Fair- maire) in North America. In: Proceedings from the Third Workshop on Genetics of Bark Beetles and Associated Microorganisms, B. Bentz, A. Cognato, and K. Raffa (Eds.). Cappaert, D., D.G. McCullough, T.M. Poland, and N.W. Siegert. 2005. Emerald ash borer in North America: a research and regulatory chal- lenge. American Entomologist 51:152–165. Haack, R.A., E. Jendek, H. Liu, K.R. Marchant, T.R. Petrice, T.M. Po- land, and H. Ye. 2002. The emerald ash borer: a new exotic pest in North America. Newsletter of the Michigan Entomological Society 47:1–5. Herms, D.A., D.G. McCullough, D.R. Smitley, C.S. Sadof, R.C. William- son, and P.L. Nixon. 2009. Insecticide options for protecting ash trees from emerald ash borer. North Central IPM Center Bulletin. 12 pp. 30.3 ± 22.0 A
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