204 Erratum: Efficacy of Arborjet VIPER Microinjections in.] and ranged from 18.8 to 85 cm (7.5 to 34 in.). All the microinjected trees were established urban forest trees. Ports used in this study were cylindrical, barbed inserts with rubber septa that were set circumferentially into the trunk flare area. To place the ports, a portable 18.0 v Ryobi drill (model# HP1802M) with a 0.74 cm (0.3 in.) brad point bit was used to drill 2.5 cm (1 in.) into the active sapwood. The ports, 1 cm (0.4 in.) length x 0.9 cm (0.36 in.) diameter, tapering toward the proximal end, were configured with a “lip” to limit the depth of its setting at the current-year xylem. Set correctly, the port creates a small reservoir (1.5 × 0.75 cm [0.6 × 0.3 in.]) into which the solution is injected and from which it infuses into the tracheary elements of the tree. The probelike needle of the Arborjet device pierces the septum of the port and delivers up to 3.0 mL (0.09 oz) per trigger pull. Using the described port arrangement, 6.0 mL (0.18 oz) were deposited per port. For each tree, the total number of injection sites was determined using the formula dbh/3. Precise dosage delivery was aided by a pressure gauge at the tip of the injection device and 10 mL (0.3 oz) dose cartridge, or Dose-Sizer™. The tip gauge registered hydraulic pressures in the sapwood of Tsuga canadensis from 45 to 450 psi. Collecting Samples from Hemlock Twig samples were harvested in fall 2002 (between 22 October and 5 November) from 24 treated hemlocks randomly selected in the Winchester, Massachusetts, U.S. area. In addition, 24 nontreated trees were sampled at random during the same interval for HWA mortality assessment. Eight samples measuring 45 to 60 cm (18 to 24 in.) in length per tree were cut, bagged, labeled, refrigerated (at approximately 7.2°C [45°F] and 60% relative humidity), and evaluated within 3 days. Samples were taken using a no. 180 ARS Long Reach pruner capable of 3 m (3.3 ft) extension, effectively reaching to 4.8 m (5.3 ft) into the canopy. Samples were taken from infested branches, typically from the lower to mid canopy. Evaluating Efficacy Microinjection treatment efficacy was evaluated on the basis of insect mortality. HWA mortality was based on a percent- age of dead insects (adults and nymphs) as determined by microscopic inspection of 240 45 cm (18 in.) samples infested with HWA. Insects were considered dead if they appeared desiccated, hard, discolored (darkened), and/or not responsive to stimuli (appendage, stylet, probe). The mortality percentage is the number of dead adelgids divided by total observed. HWA density is the number of live adelgids observed per linear centimeter of twig sample. RESULTS Percentage of HWA Mortality In samples from treated trees, observed mean adelgid mortality was 85% for 104 samples, with a range of 58.2% ©2005 International Society of Arboriculture to 100%. Two-thirds of treated samples had 80% mortality or greater. For untreated samples, the mean mortality in 88 samples was 37.9%, with a range of 6.9% to 81.7%. Mortality of 80% or greater was observed in only 2.3% of the untreated samples (Figure 2). Figure 2. Boxplot of HWA mortality percentage in treated and control samples. The data were analyzed using a Student’s t-test to determine the difference between the mean percentage mortality of the treated and control samples. Minitab calculated a t-value of 19.50 and a p-value of 0.000. We therefore have a 90% level of confidence that the true difference in the mean percentage of mortality of HWA of the treated and control populations ranges from 43.1% through 51.1%. Live HWA Density Live HWA density was calculated for each sample by dividing the number of live adelgids by the sample length. Live HWA density is expressed in live HWA per linear centimeter. The mean live HWA density for 104 treated samples was 0.45 live HWA per linear centimeter. The range for treated samples was 0 through 2.6 live HWA per linear centimeter. Of all treated samples, 87.5% had less than 1 live adelgid per linear centimeter (Figure 3, top). The mean live HWA density for 88 control samples was 1.99 live adelgids per linear centimeter. The range for the control samples was 0.039 through 8.73 live HWA per linear centimeter. Only 31.8% of the control samples had less than 1 live HWA per linear centimeter (Figure 3, bottom). A Student’s t-test was used to determine the difference of the mean live HWA density on the treated and control samples. Minitab calculated a t-value of 9.18 and a p-value of 0.000. (Note: There were two outlier values in the treated
July 2005
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