Arboriculture & Urban Forestry 33(5): September 2007 343 green ash and 13 to 46 woodpecker attacks/m2 (1.2 to 4 per ft2) on white ash over the 3-year period. By 2005, all Windemere trees had woodpecker attacks and, on average, woodpeckers preyed on 27% of the A. planipennis in these trees. Green ash trees at Lakeside, surveyed in 2005, had signifi- cantly more exit holes and woodpecks per meter squared than white ash trees with an average of 22.8 (±6.86 SE) per meter squared [2.1 (±0.64 SE) per ft2] for green ash and 5.9 (±1.02 SE) per meter squared [0.6 (±0.09 SE) per ft2] for white ash (S94.0; df1,15; P0.0180). On green ash trees, 56% of the average total density was comprised of exit holes, whereas woodpeckers attacked the remaining 44% of the A. planipennis. On white ash trees, exit holes made up 29% of the average total density and woodpecker attacks made up 71% of A. planipennis density. Overall, using the Butzel, Larned, and Windemere data, canopy dieback increased as the density of A. planipennis exit holes and woodpecker attacks increased. A positive and sig- nificant linear relationship existed between these two vari- ables for green ash, for white ash, and the two species com- bined (Figure 4). In general, if dieback was less than 30%, fewer than 30 exit holes and woodpecker attacks per meter squared (3 per ft2) were found. If dieback was less than 50%, the density of exit holes and woodpecker attacks ranged from 30 to 60 per m2 (3 to 6 per ft2) (Figure 4). Two dead trees had densities as low as 37 to 50 exit holes and woodpecker attacks per meter squared (3 to 5 per ft2). Overall, on trees with more than 90% dieback, the density of exit holes and wood- pecker attacks ranged from 60 to 155 per m2 (6 to 14 per ft2) (Figure 4). White versus Blue Ash Woodlot Trees The white ash trees in both woodlots were heavily infested and declining or dying, whereas blue ash trees of similar size had much lower exit hole and woodpecker attack densities. In 2004, white ash trees in the Plymouth Township woodlot had significantly more A. planipennis exit holes and woodpecker attacks per meter squared than blue ash trees with an average of 80.1 (±20.65 SE) per m2 [7.4 (±1.92 SE) per ft2] for white ash and 11.5 (±7.83 SE) per m2 [1.1 (±0.73 SE) per ft2] for blue ash (S 16.0; df 1,8; P 0.0079). Exit holes and woodpecker attacks were found on branches and trunks of both species. Exit holes comprised 70% and 61% of the av- erage total A. planipennis density in white ash and blue ash trees, respectively, whereas woodpecker attacks accounted for 30% and 39% of the A. planipennis in white and blue ash, respectively. Percentage of phloem surface area covered by A. planipennis larval galleries ranged from 0% to 100% in white ash, with an average of 39% (±10.9 SE), and from 0% to 40% in blue ash, with an average of 8% (±5.7 SE). Significantly more phloem area was covered by galleries in white ash than in blue ash (S 18.0; df 1,8; P 0.0278). Similarly, in the Superior Township woodlot, white ash trees had significantly more exit holes and woodpecker at- tacks per meter squared than blue ash in 2004 (S 30.0; df 1,7; P 0.0079) and 2005 (S 10; df 1,6; P 0.0143) (Figure 5). There was a significant increase in the density of exit holes and woodpecker attacks from 2004 to 2005 for the white ash trees in the Superior Township wood- lot (S 26.0; df 1,6; P 0.0143), but not for the blue Figure 4. Percent canopy dieback and number of Agrilus planipennis exit holes (exits) and woodpecker attacks (WPs) per meter squared for 25 green ash and 24 white ash trees (49 trees total) surveyed at three residential sites in 2003 and 2004. Figure 5. Mean (±SE) number of Agrilus planipennis exit holes (exits) and woodpecker attacks (WPs) per meter squared for white and blue ash trees at Superior Town- ship in 2004 and 2005. *Significant differences between white and blue ash trees (Wilcoxon rank sum test; P < 0.05). ©2007 International Society of Arboriculture
September 2007
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