Arboriculture & Urban Forestry 38(2): March 2012 infestations. Six treatments were assigned in two randomized blocks, each of which was replicated eight times. The treatments were (1) untreated controls (UTC), (2) IMA-jet [5% (g/g) imi- dacloprid SL systemic insecticide; Arborjet, Inc., Woburn, Mas- sachusetts, U.S.] low rate, (3) IMA-jet high rate, (4) IMA-jet low + Merit® 75 WSP [75% (g/g) imidacloprid; Bayer Environmental Science, Research Triangle Park, North Carolina, U.S.] soil injec- tion, (5) IMA-jet high + Merit soil injection, and (6) Merit soil injection alone. Soil injections were made using the Kioritz® (Ki- injector were used to make the tree injections. Low rates of imidacloprid were applied at 0.15 g a.i. /2.5 cm DBH, high rates were applied at 0.30 g a.i. /2.5 cm DBH, and soil in- jections were made at 1.45 g a.i. /2.5 cm DBH. QUIK-jet injec- tions applied 3 ml IMA-jet per 2.5 cm DBH and the TREE I.V. applied 6 ml IMA-jet per 2.5 cm DBH. For example, in a 50 cm DBH tree, 60 and 120 ml of IMA-jet were applied for low and high dose injections, respectively. The IMA-jet formulation was applied at rates lower than the 4 to 8 ml (0.2 to 0.4 g) a.i. /2.5 cm DBH label use recommendations. Tree injections of imida- cloprid were applied as formulated. The injection site was made into the trunk flare (i.e., basally) using a 9 mm Brad point bit, drilled 3.75 cm into the sapwood and fitted with an Arborplug™ (a backflow prevention device) to create a 2.5 cm3 oritz Corporation, 7-2, Suehirocho 1 –Chome, Ohme, Tokyo, 198 Japan) injector; applications were made 30–90 cm away from the tree bole, where the fibrous roots were most likely concen- trated. Each Merit 75 WSP 45.4 g packet was mixed in 960 ml of water, per label instructions. The Arborjet® QUIK-jet® Tree I.V. and the capacity site to mitigate for slow uptake in the sapwood tracheids. The num- ber of application sites varied from 15 to 20 cm of stem circum- ference for the QUIK-jet and Tree I.V., respectively. Treatments 43 were applied on August 29–30, 2007 at the Biltmore Estate. The imidacloprid treatments were timed to coordinate with the re- sumption of adelgid activity following summer aestivation. The amount of time for each treatment to be applied was recorded. Tree Assessments Branch samples were taken from trees each November from 2007 to 2010 (at approximately 70, 435, 800, and 1,165 days after treat- ment) for assessment and imidacloprid residues (Table 1). Autumn was selected for sampling because tree growth was expected to be complete, HWA resumed development following summer aesti- vation (therefore were easier to assay), and before low tempera- ture events could adversely affect HWA survival. Four branches were cut, each between 40 and 60 cm in length, from the mid-tree canopy in four sectors by aerial lift truck, and shipped to Arborjet, Inc. for evaluation. Branches were refrigerated at 4.4°C until the assessments were conducted. Digital scans were made of all of the branch samples, using a Canon Color Image Scanner (CanoScan 8800F); the digital images captured the temporal changes in tree condition. Percent tip growth was estimated for each branch sam- pled, and the mean calculated for each tree. Tip growth was deter- mined on a percentage basis, adapting the method by Webb et al. (2003). Within a treatment, percentage of branches with new tip growth was determined by dividing the number of tips with new growth by the total tips counted, multiplied by 100. Each branch was then cut into five shorter branchlets (terminal, plus four lat- erals) to evaluate the number of HWA per cm of new growth. HWA infestations were assessed by microscopic examination. The number of HWA on twigs with needles was counted, branch length was measured, and the value HWA /cm was calculated. Table 1. Treatments, imidacloprid residues in µg/g (ppm), percent tip growth, and HWA infestation per centimeter of branch. The LC50 value for HWA is 0.30 µg/g (Cowles et al. 2006). Per treatment, percent tip growth is a measure of the mean number of tips on branches with new growth. Year 2007 Treatment Untreated controls IMA-jet Lo IMA-jet Hi IMA Lo + imidacloprid soil IMA Hi + imidacloprid soil MERIT soil 2008 Untreated controls IMA-jet Lo IMA-jet Hi IMA Lo + imidacloprid soil IMA Hi + imidacloprid soil MERIT soil 2009 Untreated controls IMA-jet Lo IMA-jet Hi IMA Lo + imidacloprid soil IMA Hi + imidacloprid soil MERIT soil 2010 Untreated controls IMA-jet Lo IMA-jet Hi IMA Lo + imidacloprid soil IMA Hi + imidacloprid soil MERIT soil means are presented in table. z µg/g 0.01z 0.20a 0.17a 0.22a 0.86a 0.14a 0.02z 1.75ac 3.79a 1.32abc 3.27a 0.33b 0.09z 2.04b 3.61ab 3.70ab 6.54a 3.14ab 0.15z 1.35b 1.83b 3.54ab 4.76a 2.37ab % Tip growth 5.60b 6.07b 3.41b 13.04b 7.74b 1.62b 2.59b 12.54b 19.60b 30.58a 33.57a 2.61b 36.90b 72.27a 70.29a 81.70a 79.77a 41.70b 48.51b 90.01a 84.64a 90.01a 90.01a 60.20b HWA/cm 0.28b 0.17b 0.00b 0.21b 0.00b 0.11b 1.80b 1.82b 0.38b 0.92b 0.72b 2.81b 1.42b 0.04a 0.08a 0.03a 0.03a 0.21a 1.79c 0.12a 0.19a 0.00a 0.00a 0.26b Notes: n = 8. Means followed by the same letter are not significantly different at P < 0.05. Percentage data transformed (asin (sqrt (x/100)))*57.3 prior to ANOVA. Actual Not included in statistical analyses (n < 8). ©2012 International Society of Arboriculture
March 2012
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