28 Doccola: Stem-Injected Hemlock Against Hemlock Woolly Adelgid in the GRSM Table 1. Treatments, methods of application, number of replicates, dosage per 2.5 cm DBH, and milliliters per injection site applied. Treatment IMA-jet IMA-jet UTC Merit 75WP Method Air Hydr/#4 Arborplug Ecoject Untreated check Soil drench Tree ID AHA ECO UTC DRE N 10 10 10 10 Dose g/2.5 cm DBH 0.2 0.2 0 1.42 mL/2.5 cm DBH mL/inject site 4 4 0 NA 8 8 0 NA Ste. Marie, ON) or by Air Hydraulic injector (Arbor- jet, Inc.). Applications were made between June 24 and June 28, 2010. The Air Hydraulic injector is a liquid delivery sys- tem that utilizes compressed air to apply formulations directly to the vascular tissue. The No. 4 Arborplug® was used in conjunction with the injector and is designed to prevent the chemistry from contacting the meristematic tissues and to minimize phytotoxic- ity. The Ecoject uses a refillable 8-mL-capacity canister and removable injector tip for application. Tree injec- tions were applied at 8 mL and inserted every 15 cm of basal trunk circumference; the gram active ingredi- ent (GAI) applied was 0.2 per 2.5 cm DBH. The basal drenches were applied within 0.6 m of the base of the hemlock trunk at 1.42 GAI per 2.5 cm DBH. Each treatment and an untreated control were replicated 10 times in a completely randomized design. A summary of the treatments is presented in Table 1. Following treatments, 4 branches (~48 cm length) were taken from each of 4 quadrants each November from the mid- to upper canopy in order to evaluate twig and foliar growth, HWA density, and percent HWA mor- tality. Each of the 4 samples was cut into 5 subsam- ples, each consisting of 3-year growth increments, from the branch terminal to the laterals. Thus each tree generated 20 subsamples each year from which to record tree responses. No branch samples were taken in the spring of 2011 due to the poor overall condition of the trees (Figure 1). We counted the number of adelgids on the 3-year branch samples and measured branch lengths. From these two metrics we calculated the number of HWA per cm of branch, and tree growth over time. We estimated the percentage of growing points per branch sample per treatment. Statistical Methods For both 3-year growth (cm) and HWA per cm, the data collected on 20 subsamples in each of years ©2021 International Society of Arboriculture 2012, 2013, and 2014 were averaged for each tree and year, and resulting means for growth and HWA counts were subjected to repeated measures analysis of variance (RM ANOVA) using PROC MIXED (SAS Inc., Cary, NC, USA). Fixed effects in the RM ANOVA model were Trt, Year, and Trt*Year. Multi- variate ANOVA, heterogeneous compound symme- try (CSH), and split plot (CS) were compared using the Bayesian Information Criterion (BIC) produced by PROC MIXED (SAS) and the model with small- est BIC was selected. The simple split plot ANOVA (with year viewed as a subplot factor) was found to be adequate for cube-root-transformed HWA counts, while the CSH model was selected for square-root- transformed 3-year growth means. Comparisons among treatment means were carried out using the LSD pro- cedure at significance level 0.05, with results reported by year if Trt*Year interaction was significant. Data were transformed before carrying out analy- sis of variance (ANOVA) in order to achieve approx- imate homogeneity of variances across treatments. The arcsine transformation was applied to the propor- tion of terminals showing growth. ANOVA results are given for the transformed data and back-transformed treatment means are reported in graphs. In addition, treatment comparisons were carried out separately for each year (in MINITAB Version 17, Minitab, Inc., State College, PA). The grouping information used was the Fisher LSD Method at the 95% level of confidence. RESULTS HWA per cm Year and Treatment effects were strong (F2,68 = 37.61, P < 0.001 and F3,34 = 37.61, P < 0.001, respectively) due mainly to higher counts for the control treatment, which decreased from 2012 to 2014. The interaction effect Trt*Year was also significant (F6,68 0.002). = 3.75, P =
January 2021
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