176 Doccola et al.: Systematically Applied Insecticides for Treatment of Erythrina Gall Wasp ing mouthparts (e.g., emerald ash borer, Smitley et al. unpub- lished), emamectin benzoate demonstrated greater activity (~2x) to imidacloprid. In this design, the emamectin benzoate treated trees received ~0.5x the grams active ingredient compared to the imidacloprid treated trees. Following label instructions, the em- amectin benzoate formulation was mixed with an equal volume of water at application, while IMA-jet was applied as formulated. Basal injections into the stem or root flare (Figure 2) occurred on January 29 or 30, 2007 using the Tree I.V. system. The Tree I.V. has a 650 ml liquid capacity that is pressurized to 172–241 kPa (25–35 PSI) at the time of application and distributed among 4 to 16 needle assemblies based on tree diameter. A 9 mm (3/8 in) diameter bit was used to drill into the sapwood to a depth of ~15 mm (5/8 in.) at a right angle to the stem. Once the hole was drilled, an Arborplug was inserted to create the injection site. The Arbor- plug is designed to prevent backflow of insecticide formulation from the tree and accepts a 1.6 mm diameter injector needle; the Arborplug remains in the tree following treatment. Application sites were located every 15–20 cm (6–8 in) of tree circumference. The duration of time necessary for the bottle and lines to empty was considered uptake time and was recorded for each tree. Mean uptake times for IMA-jet and emamectin benzoate formulations were compared by t-test to determine significant differences. response variables, one-way analysis of variance (ANOVA) was used on pre-treatment data to ensure that treated tree popula- tions were not different in the responses measured. Treatment effects were evaluated by subjecting mean within-tree differ- ences at 0 and 13 months to one-way ANOVA (e.g., Mathews et al. 1990). Mean separations were done using Tukey’s HSD. In addition, paired t-tests were used to evaluate changes in canopy density for each treatment separately; these data were arcsin transformed prior to analysis to better meet statistical as- sumptions. For categorical response variables, Fisher’s Exact Test was used to evaluate treatment effects; separate analyses were conducted for data gathered at time of treatment and 13 months. A paucity of trees in the two categories of least injury (0 and 1%-25%) led to analysis on only three categories: < 50%, 50%–75% and 76%–100%. Uptake times for the two insecticide formulations were compared using a t-test. Statistical analy- ses were conducted using MINITAB (Version 15, Minitab, Inc. State College, PA, U.S.) or Stata (Version 10, StataCorp, Col- lege Station, TX, U.S.) with significance accepted when P < 0.05. RESULTS Figure 2. Native wiliwili on Maui were stem-injected using Arbor- jet Tree I.V. equipment. Insecticide residues were determined from foliage samples collected from each tree at the four cardinal directions at time of treatment, and 35 d and 13 months thereafter (Table 1). Foli- age samples were taken from the outer edge of the lower canopy. Generally two samples were analyzed and their mean reported, but when sample weights were too little they were combined as needed to obtain at least 1 g dry weight. Imidacloprid resi- dues were determined by high-pressure liquid chromatogra- phy (HPLC) following freeze-drying, grinding and extraction with acetonitrile. Leaf tissues for emamectin benzoate residue analyses were prepared similarly and followed a simplified ver- sion of the procedures described by Takai et al. (2003); residues were determined using fluorescence HPLC. Values are reported in parts per million (PPM) and are uncorrected for the propor- tion of chemical recovered from samples, which was ~0.50. The minimum detection limit for emamectin benzoate was 0.01 PPM. As previously described, treatment effects were evaluated us- ing canopy foliage density, the ratio of galled to total leaf area and branch tip dieback as response variables. For continuous ©2009 International Society of Arboriculture Mean formulation dosages and uptake times were 131 ml in 21.6 minutes for IMA-jet and 172 ml in 16.7 minutes for the diluted emamectin benzoate formulation. Dosages of active ingredients follow as 6.6 g imidacloprid and 3.4 g emamectin benzoate. Despite total injected volumes differing (as per label instruc- tions), uptake times were not significantly different between insecticide treatments (P = 0.184, t-test); emamectin benzo- ate infused into tissues at a higher rate (mean of 13.6 ml/min) compared to IMA-jet (mean of 8.8 ml/min) though this was not statistically significant (P = 0.065). The difference in flow rates is likely a function of formulation dilution rather than canopy transpiration (McWain and Gregory 1973). Although transpira- tion was not measured, leaf area reflects surface transpiration area (Santiago et al. 1999) and pretreatment canopies were simi- lar among treatments (see below). Tree canopy evaluations (foli- age density, galled to total leaf area, branch tip death) did not differ among treatments at treatment time (P > 0.05; Table 1). Canopy foliage density at time of treatment averaged 26.3% (range from 9.14%–49.92%) for all study trees. Both untreated ( = 25.8 ± 2.3% versus = 15.0 ± 1.6%) and emamectin ben- zoate treated ( = 27.7 ± 2.9% versus = 19.9 ± 2.1%) trees lost significant canopy density between sample periods at 0 and 13 months (P < 0.05; Figure 3A). However, injection with imidacloprid stabilized loss of canopy; there was no sig- nificant difference in canopy foliage density at time of treat- ment ( = 25.3 ± 2.8%) and 13 months ( = 24.9 ± 3.4%; P = 0.77). Analysis on differences in canopy density revealed that imidacloprid treatment ( = 0.3% loss) was best, but not significantly better than emamectin benzoate ( = 7.8%), which was not significantly better than no treatment ( = 11.6%). Ratio of galled to total leaf area provided additional evidence for the superiority of IMA-jet in this application. Trees assigned different treatments did not differ in pre-treatment galled to to- tal leaf areas (Table 1). All treatments showed a numerical in- crease in galled to total leaf area at 13 months relative to pre- treatment, demonstrating the pressures realized from EGW at the study site. However, canopy changes in the imidacloprid treatments alone were insignificant. Untreated trees showed a
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