396 Tanis and McCullough: Evaluation of Xylem Discoloration in Ash Trees unlike neonicotinoid products that require annual application, emamectin benzoate is efficacious for up to three years (Smitley et al. 2010a; McCullough et al. 2011, DGM, unpublished data). Reduced application frequency means fewer opportuni- ties for wounding. Although practicing arborists would rarely, if ever, treat trees with TREE-äge on an annual basis, researchers were able to assess trees injected annually for six consecutive years as part of a long-term research project on EAB dynamics. On average, the seven trees in the six- year study group had 29 injection sites per tree, yet only one tree in this group had damage associated with two of its 23 injection sites. The majority of trees in the six-year study had at least four years of wood growing over sites injected in 2008 and 2009. Many studies have reported the existence of tis- sue discoloration adjacent to trunk injection sites (Smith and Lewis 2005; Mota-Sanchez et al. 2009; Doccola et al. 2010; Tanis et al. 2012), but the integ- rity of discolored tissue has not been previously assessed. In this study, multiple lines of evidence indicate discoloration surrounding injection sites was simply a stain and not indicative of tissue dam- age. Microscopy results indicated the integrity of xylem tissues immediately surrounding injection sites was sound, regardless of ash species, insecti- cide application rate, or the number of injections. In addition, when samples were prepared for micro- scopic examination, much, if not all of the discol- oration dissolved when samples were soaked in ethanol. If discoloration was indicative of wound- ing, it would presumably persist despite immer- sion in ethanol. Researchers also found discolored tissues surrounding injection sites effectively trans- located insecticide applied in subsequent years, which would not have been possible if discoloration represented barrier zone formation (Shigo 1977). The six injection sites that were drilled and plugged but not injected with insecticide had no associated discoloration, further suggesting the formulated insecticide product was the source of discoloration. In hindsight, it would have been advantageous to inject water to assess the wound response exclu- sively associated with drilling, insertion of the plastic plug, and injection pressure. In other mac- roinjected ash trees, concentration of imidacloprid in discolored tissues was much higher than in adja- cent unstained tissues (Mota-Sanchez et al. 2009; ©2016 International Society of Arboriculture Tanis et al. 2012), and a previous study on green ash trees reported discolored tissues were sound even four years aſter injection (Doccola et al. 2011). In this study and others, tissue discoloration diminished with tree height above the injection site (Mota-Sanchez et al. 2009; Tanis et al. 2012). Following the discoloration upward through the cross sections cut from the trees, discolored areas became smaller and paler, indicating the volume of translocated insecticide decreased with height. Previous studies with high concentrations of imida- cloprid, a compound with relatively low solubility, showed a reservoir of insecticide can persist for multiple years around injection sites, suggest- ing some product remains in xylem near the injection sites (Mota-Sanchez et al. 2009; Tanis et al. 2012; Aćimović et al. 2014; Aćimović et al. 2015). In the current study, EB-high trees received at least twice as much product (mixed with an equal amount of water) as the EB-low trees and the height of discolored tissue was at least twice that observed in the EB-low trees, even though EB-low trees were injected under greater pres- sure. This suggests vertical discoloration was a function of the volume of insecticide applied rather than an indicator of application pressure. In contrast, discoloration width and length did not vary between EB-high and EB-low trees. This indicates lateral movement of insecticides in the lower 50 cm of the trees was unaffected by vol- ume or the pressure applied during application. Given the continued spread of EAB across North America and the increased use of systemic insecti- cides for EAB and other pests, understanding how trunk injection systems and insecticide products affect tree health over time will be important. This study showed green ash and white ash trees were rarely harmed by the trunk injection process. While the cause of internal discoloration is not known, it seems likely that it could result from inert dyes used in the emamectin benzoate formulation. Perhaps most importantly, discoloration was not indicative of an ash tree compartmentalization response that could impede translocation. Other systemic insec- ticides, including emamectin-benzoate-based prod- ucts, along with an array of trunk injection devices, are available for landscape trees. Whether these results extend to other systemic insecticide products or injection tools will require additional evaluation.
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
