394 Tanis and McCullough: Evaluation of Xylem Discoloration in Ash Trees and EB-high trees were not significant (P = 0.66) (Table 1). The number of injections did not vary between ash species (P = 0.75) nor was the species × insecticide rate interaction significant (P = 0.37). Presence of new xylem tissue over the injection sites did not vary between tree species (P = 0.30), insecticide application rates (P = 0.21), injection frequency (P = 0.17), nor were the interactions sig- nificant. Xylem was growing over 134 (58%) of the injection sites. Among the 46 trees examined in this study, 39 (85%) had new xylem growing over at least one injection site, and 37 (80%) had new tissue growing over multiple injection sites (Table 1). Presence of secondary wounds, such as external bark cracks or internal necrosis, was not affected by ash species (P = 0.29) or insecticide rate (P = 0.23) nor were interactions significant. Only 12 of the 233 injection sites (five on white ash trees, seven on green ash trees) were associated with ver- tical cracks in the outer bark. Three of the 13 EB- low trees treated only in 2008 had one to two bark cracks associated with injection sites, but no internal cracking or necrosis were found on these trees, nor were they found on the other 10 EB-low trees. None of the 11 EB-low trees treated in both 2008 and 2009 had internal cracks or necrosis, and only one injection site (on a white ash) was associated with a crack in the outer bark. Among the 11 EB-high trees treated only in 2008, one tree had three cracks in the outer bark, but none of the trees had internal cracks or necrosis. One of the 11 EB-high trees treated in both 2008 and 2009 had two cracks in the outer bark, but none of the trees had internal cracks or necrosis. The number of bark cracks was higher in trees treated only in 2008 (nine bark cracks) (F = 5.57; df = 1, 38; P = 0.024) than in trees treated in 2008 and 2009 (three bark cracks) (Table 1). Length and width of discolored xylem did not vary between ash species (P = 0.57 and P = 0.28, respectively), application rates (EB-low, P = 0.93; and EB-high, P = 0.09), or number of applica- tions (2008, P = 0.45; 2008 and 2009, P = 0.82), nor were the interactions significant. Discoloration length averaged (±SE) 31.6 ± 3.25 mm while dis- coloration width averaged 13.7 ± 1.22 mm. Area of discolored xylem around injection sites aver- aged 9.2 ± 0.86 cm2 and 8.3 ± 0.91 cm2 EB-high trees treated in 2008 or in both 2008 and 2009, respectively, and 6.4 ± 1.01 cm2 0.85 cm2 per site for and 5.9 ± per site for EB-low trees treated in 2008 or in both 2008 and 2009, respectively. Discolor- ation extended 63% higher (F = 61.66; df = 1, 38; P < 0.001) in the trunk of EB-high trees (32.3 ± 2.4 cm) than in EB-low trees (12.1 ± 0.96 cm) but was similar between ash species (P = 0.61), between trees treated only in 2008 or in both 2008 and 2009 (P = 0.62), and none of the interactions were sig- nificant. At a height of 15.0 cm above injection sites, area of discoloration averaged 4.4 ± 0.93 cm2 ± 0.55 cm2 and 3.9 and in both 2008 and 2009, respectively, and 1.0 ± 0.33 cm2 in 2008 and in both 2008 and 2009, respectively. Six-Year Study: Green ash tree diameter did not differ between trees treated with high or low insecticide application rates (P = 0.51), trees injected annually from 2008–2013 Table 1. Number of green ash and white ash trees injected with a low rate (0.1 g a.i. per 2.5 cm DBH) or medium-high rate (0.4 g a.i. per 2.5 cm DBH) of emamectin benzoate (TREE-äge, 4.0%, ArborJet, Inc., Woburn, Massachusetts, U.S.), the total number of injection sites for those trees, the number and percentage of injection sites overlaid with new xylem tissue, and injection sites with associated wounds (external bark cracks, internal xylem necrosis, and evidence of pathogen infection). Trees in the two-year study were treated once in 2008 or in both 2008 and 2009. Trees in the six- year study were treated in 2008 and again in 2011, or annually from 2008 to 2013. Treatment Two-year study EB High EB Low EB High EB Low Six-year study EB High EB Low EB High EB Low No. of trees 11 13 11 11 4 4 3 4 ©2016 International Society of Arboriculture Years treated 2008 2008 2008 and 2009 2008 and 2009 2008 and 2011 2008 and 2011 2008–2013 2008–2013 Total no. injection sites 50 42 77 64 35 37 86 116 No. overlaid with new xylem 30 (60%) 29 (69%) 44 (57%) 31 (48%) 35 (100%) 37 (100%) 86 (100%) 116 (100%) No. with wounds 3 (6%) 9 (21%) 2 (3%) 1 (2%) 1 (3%) 1 (3%) 2 (2%) 0 (0%) per site for EB-high trees treated in 2008 and 2.9 ± 1.83 for EB-low trees treated
November 2016
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