Arboriculture & Urban Forestry 46(5): September 2020 Imidacloprid residues differed significantly based on treatment (full or half application rate) and on tis- sue type (leaves, stems, or roots), and there was no significant treatment × tissue interaction (Table 1a). Residues of the metabolite imidacloprid olefin did not differ based on treatment or on tissue type, and again, there was no interaction (Table 1b). The metab- olite dihydroxy imidacloprid was below the LOD and so was not analyzed. Root tissue from trees treated with a soil drench of imidacloprid contained over 7 times the residue found in leaf tissue, regardless of application rate, and although leaf and stem tissue did not differ statisti- cally, leaf tissue contained 3 to 5 times higher resi- dues than did stem tissue, again regardless of application rate (Table 2a). For dinotefuran, 33 of the 55 samples had residue concentrations above the limit of detection (0.43 ppb), ranging from 0.47 to 33.3 ppb. Of the 18 leaf and 351 18 root samples, 16 had measureable dinotefuran res- idues. Of the stem samples, only 2 had dinotefuran residues above detectable limits. In contrast to imidacloprid, dinotefuran applied at full or half rates resulted in no significant differences in residues 5 weeks post-application (Table 1c). There were, however, significant differences based on tis- sue type, but no interaction between the two factors. Dinotefuran applied as a trunk spray at the full rate resulted in significantly higher residues in both leaf and root tissue relative to stem tissue; leaves and roots of dinotefuran-treated trees contained over 40 times the residues found in stem tissue. Dinotefuran applied at the half rate was similar (Table 2b). Phloem tissue consumption by EAB larvae in treated trees was lower than in untreated trees, regard- less of chemical insecticide and application rate (χ2 = 26.26; df = 4; P < 0.0001)(Figure 2). Trees treated with either insecticide applied at either the full or half Table 1. Analysis of insecticide residues in parts per billion (ppb) 5 weeks post-treatment in leaf, stem, and root tissues of ash trees treated with (a) imidacloprid applied as a soil drench at full rate (2.64 mL/L H2 lite (b) imidacloprid olefin, and (c) dinotefuran applied as a trunk spray at full rate (90 g/L H2 O) and half rate (1.32 mL/L H2 (a) Imidacloprid treatment (full vs. reduced rate) tissue (leaf, stem, root) treatment × tissue (b) Imidacloprid olefin treatment (full vs. reduced rate) tissue (leaf, stem, root) treatment × tissue (c) Dinotefuran treatment (full vs. reduced rate) tissue (leaf, stem, root) treatment × tissue F statistic F1,40 F2,40 F2,40 χ1 χ2 χ2 χ1 O) and half rate (45 g/L H2 = 8.13 = 98.34 = 0.63 Wald Chi-Square = 0.0671 = 1.0288 = 0.1597 Wald Chi-Square = 0.0003 χ2 χ2 = 11.1935 = 0.4052 O), its metabo- O). Pr > F 0.0069 0.0001 0.5369 Pr > ChiSq 0.7956 0.3105 0.6895 Pr > ChiSq 0.9859 0.0037 0.8166 Table 2. Insecticide residue in parts per billion (ppb)(raw mean [SE]) in ash foliage, stem, and root tissues 5 weeks following application of (a) imidacloprid applied as a soil drench at full rate (2.64 mL/L H2 O) and half rate (1.32 mL/L H2 from calculations). Tissue type Leaf Stem Root n 9 9 9 Full rate (a) imidacloprid n 54.09 (12.59) a 15.03 (1.98) a F2,24 406.22 (115.04) b = 10.39/0.0006 9 9 8 Half rate 50.71 (18.64) a 9.28 (2.82) a 371.81 (120.22) b F2,24 = 7.98/0.0022 n 9 1 9 Full rate (b) dinotefuran n 5.12 (1.27) 1.12 5.37 (1.23) 7 1 6 Half rate 5.26 (1.09) 1.15 5.07 (1.46) columns followed by the same letter do not differ) and (b) dinotefuran applied as a bark spray at full rate (90 g/L H2 rate (45 g/L H2 O)(means within O) and half O)(n = sample size used to calculate raw means, where values below the limits of detection have been dropped ©2020 International Society of Arboriculture
September 2020
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