Arboriculture & Urban Forestry 35(4): July 2009 bined with the low amounts of pesticides used in trunk injection makes this method of pest control attractive to stakeholders. Additionally, there is a need to investigate the insecticide dos- age required to maintain the desired level of control, as some stake- holders (public and private) will use this information for cost analysis when making decisions on the treatment of important or significant trees. This paper reports the collaboration of Bayer Environmental Science Australia, the University of Sydney, and the Sutherland Shire Council in evaluating the efficacy of trunk injected imidacloprid for the control of T. peregrinus on an urban planting of E. scoparia. MATERIALS AND METHODS Mature E. scoparia trees growing along a residential street in Sutherland, a southern suburb of Sydney, Australia (34° 01.653’S; 151° 04.014’E; Alt. 89 m) were utilized in this trial. These trees were planted in 1982 (pers. comm. Mark McCa- ughtrie) and are one of the dominant street trees in the area. Fourteen trees, situated on both sides of the street, ranging in height from approximately 10 to 30 m (30 to 100 ft) were se- lected for the trial. Trunk diameter was measured at breast height (1.3 m/51 in aboveground level), and ranged in size from 380 to 810 mm (15 to 32 in). For the purposes of this study, trees were assigned to one of four groups; control (no treat- ment) or low, mid, and high treatment concentrations (Table 1). Table 1. Tree size (diameter) and dose administered on 13th September 2004. Tree group control control control low conc. low conc. low conc. low conc. mid conc. mid conc. mid conc. mid conc. high conc. high conc. high conc. Diameter cm (in) 72 (28) 60 (24) 73 (29) 81 (32) 67 (26) 67 (26) 57 (22) 65 (26) 62 (24) 38 (15) 38 (15) 65 (26) 57 (22) 51 (20) g imidacloprid/cm (in) of dbhz 0 0 0 0.05 (0.004) 0.05 (0.004) 0.04 (0.003) 0.05 (0.004) 0.09 (0.008) 0.10 (0.008) 0.11 (0.009) 0.11 (0.009) 0.15 (0.012) 0.16 (0.013) 0.16 (0.012) z grams (oz) of active ingredient per cm of diameter at dbh (1.3 m/51 in). A solution of 200 g/L (26.7 oz/gal) imidacloprid [SilvaShield®SL, 20% (AI)] was administered with a Sidewind- er® tree injector at 2400–2700 kPa (350–400 psi). Holes were drilled approximately 40–50 mm (1.6–2.0 in) into the sap wood and distributed as evenly as possible around the circumference of the trunk at a height of approximately 1.0 to 1.5 m (3.2 to 4.9 ft). Trees receiving the low concentration treatment re- ceived doses in 5 ml (0.17 fl oz) allotments, while the so- lution delivered to the mid and high concentrations groups was administered in 10 mL (0.34 fl oz) doses. Using a cherry picker, the canopies of treated and control trees were sampled for the presence of T. peregrinus on ten oc- Figure 1. Abundance of Thaumastocoris peregrinus adults (per 40 leaves) on Eucalyptus scoparia trees over two years after treatment with three concentrations of imidacloprid. Within each sample point, means that share the same letter do not differ. Note time scale is not even. ©2009 International Society of Arboriculture RESULTS AND DISCUSSION Efficacy results were based on the comparison of popula- tion levels of T. peregrinus on treated and untreated trees over the three years of this study. The repeated measures REML analysis showed significant effects of time (P < 0.001, X2 204.53, df = 9), treatment (P < 0.001, X2 = 1115.34, df = 3) = and a significant interaction between treatment and time (P < 0.001, X2 = 180.83, df = 27). Imidacloprid effectively controlled T. peregrinus within one month of application and 193 casions over three years commencing September 15, 2004. Initially the trees were sampled on a monthly (approximately) basis and then at increasing intervals up to two years after treat- ment (at treatment and then, 1 month, 1.5 months, 3 months, 6 months, 9 months, 1 year, 1.5 years, and 2 years). A supple- mentary sample was conducted at three years post treatment. A cherry picker operator manoeuvred the 23 m (75.5 ft) tele- mation was necessary as the residuals for the raw count data did not fit the (classic) assumptions of the analysis of variance (ANOVA) and repeated measures residual maximum likeli- hood (REML) analysis such as constant variance and linearity. This log transformation provided a notable improvement in re- sidual diagnosis. REML analysis, with an unstructured model for correlation within subject across time, was used to detect statistically significant differences in the efficacy of each treat- ment over time. The unstructured correlation model was chosen due to unequal spacing between time points. The test statistic (Wald/df, symbolised by X2 ) used in this analysis is assumed to approximate the chi-square distribution. Post hoc compari- sons between means were conducted by comparing the abso- lute mean difference to the least significant difference (LSD) (Patterson and Thompson 1971; McCulloch and Searle 2001). scopic boom mounted on a 14 tonne (15.4 ton) truck over the ac- cessible canopy of each tree. From the cherry picker bucket, the sampler removed one fully expanded leaf at approximately five second intervals until a total 40 leaves were taken from each tree. These leaves were bagged, labelled and taken back to the laboratory at The University of Sydney. In the laboratory the leaves were ex- amined under a microscope and adult T. peregrinus were counted. Raw data were log10 (x + 1) transformed. The log transfor-
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