Arboriculture & Urban Forestry 46(5): September 2020 Unfortunately, as neonicotinoid insecticides, both imidacloprid and dinotefuran are under scrutiny due to concerns over their potential nontarget effects. In particular, the effects of neonicotinoids on honeybees and other pollinators has caused considerable alarm (Copping 2013; Goulson 2013; Vanbergen et al. 2013). Although deployment of imidacloprid soil drenches at label rates and lower for EAB management in for- ested situations has shown no negative effects on native hymenopteran abundance and diversity (Davidson and Rieske 2016), even short-term exposure to this chemical class could have long-term implications on pollinator colony fitness (Larson et al. 2013; Stanley et al. 2015). The focus of this study is to evaluate within-plant insecticide distribution and effects on EAB survival for plants treated with imidacloprid and dinotefuran, two commonly used chemicals for EAB manage- ment. Given the scrutiny that neonicotinoids are under, it is essential that we have a full understanding of how these compounds distribute in the plant fol- lowing application. Using imidacloprid soil drenches and dinotefuran trunk sprays applied at the full label rate and at half the label rate based on trunk diameter, EAB survival and insecticide residues within ash tis- sue were measured. Specifically, the objectives were to: (1) assess insecticide concentrations in various plant tissues 5 weeks following application; (2) assess insecticide concentrations in trees receiving applica- tions at the full and half label rates based on trunk diameter; and (3) evaluate any differences in EAB survival and phloem consumption. MATERIALS AND METHODS This work was conducted at Taylor Fork Ecological Area, a 24.3 ha abandoned pasture in Madison County, KY, situated at the interface of the outer Bluegrass and eastern Knobs regions of Kentucky. Ash thrive on the moist and fertile soils that predominate in the Bluegrass region (Campbell 1989) and were histori- cally a significant component of these forests (Whar- ton and Barbour 1973). Taylor Fork is owned and administered by Eastern Kentucky University and is characterized by open cane fields, trees in fencerows, small patches of early- to mid-succession woodlands, and sporadically occurring, large, open-grown trees with areas of dense regeneration. At the onset of the study, EAB was present in Madison County but was not yet reported at Taylor Fork, and ash showed no 349 signs of EAB-induced stress. In summer 2016, the large ash at Taylor Fork were treated prophylactically with bark sprays of dinotefuran applied at label rates to protect against EAB. In spring 2017, 3 discrete sites were established, separated by distinct topographic features and set more than 1,000 m apart. Within each site, 3 plots containing significant green ash regeneration were designated (n = 9 replicates), and in each plot 5 green ash trees (approximately 5 cm diameter at 1.37 m above ground level) were selected for treatment using a randomized block design. On May 9, selected trees in each plot received either: (i) a soil drench (1 L volume) of imi- dacloprid (Imidacloprid 2F I/T, Prime Source LLC, Evansville, IN, USA) applied at the “full rate” of 2.64 mL/L of water in 0.94 L of total solution, equiv- alent to 0.64 gai/2.5 cm diameter at 1.37 m, or DBH; (ii) a soil drench (1 L volume) of imidacloprid applied at a “half rate” of 1.32 mL/L of water in 0.94 L of total solution, equivalent to 0.32 gai/2.5 cm DBH; (iii) a basal bark spray of dinotefuran (Safari 20SG, Valent, Walnut Creek, CA, USA) applied to runoff (approximately 52 mL) at the “full rate” of 90 g/L of water, or 0.93 gai/2.5 cm DBH; (iv) a basal bark spray of dinotefuran applied to runoff (approximately 52 mL) at a “half rate” of 45 g/L of water, or 0.47 gai/2.5 cm DBH; or (v) an untreated control. Seven days after treatment, the trees (n = 15 per treatment for a total of 45 trees) were artificially infested with 3 laboratory-reared emerald ash borer eggs at heights of 25 and 50 cm above ground level for a total of 6 eggs per tree. Eggs were screened with fine polyester mesh to prevent predation, and larvae were allowed to hatch and develop for 30 days (Olson and Rieske 2018), after which plant material was processed. For processing, plants were excavated, roots were clipped and placed in sample bags, and all foliage was removed from a single south-facing branch on each tree. Samples were then stored on ice for trans- port. In the laboratory, tap water was used to wash soil from roots, followed by rinsing with distilled water. A sample of root tissue < 4 mm in diameter was then designated for chemical analysis of insecti- cide residues. The main stem of the tree was sec- tioned, and phloem tissue from the top 12.7 cm was removed for chemical analysis; the remainder was used to evaluate EAB colonization success. Thus, for each experimental tree there were root, stem phloem, ©2020 International Society of Arboriculture
September 2020
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