Arboriculture & Urban Forestry 42(6): November 2016 or injected only in 2008 and 2011 (P = 0.27), nor was the interaction of application rate and frequency significant (P = 0.13). The number of injections on EB-high and EB-low trees treated in 2008 and 2011 was similar (P = 0.31) and averaged 8.8 ± 1.25 and 9.3 ± 1.25 injections per tree, respectively (Table 1). The number of injection sites on EB-high and EB- low trees treated annually from 2008 to 2013 was also similar (P = 0.27), averaging 28.7 ± 4.26 and 29.0 ± 6.24 injections per tree, respectively (Table 1). Of the 274 injection sites assessed, only four sites on three trees (1 EB-high 2008 and 2011, 1 EB-low 2008 and 2011, and 1 EB-high annual treatment) resulted in a crack in the outer bark and none of the injection sites were associated with internal cracks or necrosis. The remaining 12 trees had no evidence of cracks in the outer bark or any other injury (Table 1). Researchers observed that at least two injection sites in each tree no longer contained the plastic plugs used during injection (i.e., plugs were forced out of trees during the healing process). One EB- high tree treated annually from 2008 to 2013 forced 16 of the 23 plugs out of the xylem. Overall, 46% of the 274 injection sites still contained the plastic plugs inserted during the injection process. All trees had new xylem tissue growing over the injection sites. Evaluation of Discolored Xylem Tissue There was no evidence that xylem discoloration was associated with injury, necrosis, or decay in the 140 samples examined with microscopy (Fig- ure 2). Cell lysis was not present in any sample and there were no visible symptoms of tissue damage or infection. The interface where dis- colored and unstained tissue were well-defined were scrutinized, as these areas might be indica- tive of a barrier zone (Shigo 1984), but we saw no evidence that trees had attempted to compart- mentalize around the discolored tissue (Figure 1). Moreover, when tissues were prepared for examination, much if not all of the discoloration disappeared from the xylem. In addition, dis- coloration was often continuous from one year’s growth to the next. For example, discoloration associated with 2008 injection sites overlapped discoloration associated with 2009 injection sites. Discoloration was continuous through the cross sections, indicating tissues discolored in 2008 were effectively translocated the product in 2009. DISCUSSION Projections suggest EAB populations will threaten at least 38 million ash trees planted in urban land- scapes in the U.S. by 2020 (Kovacs et al. 2010). Although millions of ash trees have been killed by EAB to date, advances in the knowledge of EAB biology, new systemic insecticides, and better application technology have substantially improved practitioners’ ability to protect valuable trees from EAB (Herms and McCullough 2014; Herms et al. 2014). Registration of TREE-äge in 2010, and mounting evidence of the ability of this product to provide highly effective, multiple-year control of EAB (Smitley et al 2010a; Doccola et al. 2011; McCullough et al. 2011), have reduced the costs and logistical constraints associated with treating land- scape ash trees on municipal and private property. Economic analyses have shown costs of treating and protecting landscape ash trees with TREE-äge are consistently and substantially lower than costs of removing those trees (McCullough and Mercader 2012; Vanatta et al. 2012; Kovacs et al. 2011; Kovacs et al. 2014) and ecosystem services provided by ma- ture landscape trees in urban areas are increasingly recognized (e.g., Dwyer et al. 1992; McPherson et al. 2005). Given the continued expansion of EAB, it appears likely that the number of trees treated with TREE-äge or other systemic products will increase. Evaluating potential injury resulting from trunk injections of systemic insecticides, therefore, is a concern for many arborists and landscapers. The results of the current study indicate ash trees were rarely injured as a result of TREE-äge injections made using Arborplugs and either the QUIIK-jet or TREE IV Micro-Infusion systems. Overall, of the 544 injection sites on the 61 white ash and green ash trees assessed in this study, only 3% of injection sites had evidence of external bark cracks and none had disease symptoms. These results are consistent with those of Doccola et al. (2011), who observed no “cracking, oozing, or decay” on four green ash trees (21.5 to 36.3 cm DBH) injected with TREE- äge via the TREE IV Micro-Infusion system in 2005, or on two of the trees that were re-treated in 2008. The current study included trees treated once every two years, once every three years, annually for two years, and annually for six years. Opera- tionally, ash trees are typically treated at two-year intervals with TREE-äge (Doccola et al. 2011), and ©2016 International Society of Arboriculture 395
November 2016
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
