Arboriculture & Urban Forestry 34(5): September 2008 pyriproxyfen is a growth regulator. Both are recommended for use against scale crawlers (Raupp and Davidson 2003). At weekly intervals, we monitored EHS populations. In early June, most eggs had hatched and active and settled crawlers were abundant on new foliage. We timed applications of oil and pyri- proxyfen to coincide with high densities of these life stages. There are no published accounts regarding how rapidly imi- dacloprid, dinotefuran, or acephate are transported through roots or the trunk to the canopy of hemlocks at levels lethal to EHS. However, Ford et al. (2007) reported rapidly increasing levels of water use in eastern hemlocks in the northeastern United States between May and July. Systemic insecticides were applied be- tween the middle of May and the middle of June when water use is high and translocation of insecticides is also likely to be high. Merit was applied as a soil drench on 20 May 2004. Imicide and Acecaps were applied on 3 June 2004. Arborjet applications of dinotefuron were made on 9 June 2004. As a result of the pro- longed period of egg production by bivoltine scales (Davidson and McComb 1958; McClure 1978), settled crawlers and second instar nymphs were present on trees for more than 4 months between the application of systemic insecticides and the last date that scales were sampled in October 2004. To ensure that we did not miss lethal effects of systemic insecticides as a result of slow uptake or distribution, we sampled populations of scales for two additional years, 2005 and 2006. To determine the effects of insecticides on EHS, we removed branches with hand or pole pruners from four cardinal locations on each tree. Branches were sampled from 1 to 4 m (3.3 to 13.2 ft) above the ground. Abundance of EHS was estimated by counting the number of living scales on 500 needles of terminal, young growth. We counted scales only on young growth in the lower crown because young needles in this stratum are highly preferred for colonization by EHS (McClure 1977b). This sam- pling regime was validated for estimating density of EHS by McClure (1977a, 1977b, 1977b) and used to study seasonal phe- nology, dispersal, parasitism, and competitive interactions of elongate hemlock scale (McClure 1977a, 1977b, 1977b, 1978, 1980, 1991; McClure and Fergione 1977).After branch samples were removed, they were refrigerated, taken to the laboratory, and examined microscopically. To determine viability of scales, a probe was used to remove the scale cover and pierce each scale. Scales that bled were counted as living. Those that did not bleed were considered dead. The number of living scales per 500 needles was the estimate of scale abundance. Trees were sampled on 7 July, 8 August, 7 September, and 7 October 2004; on July 7, 6 September, and 6 October 2005; and on 11 July, 7 August 7, and 12 September 2006. Before the analysis, data were examined for normality using a Shapiro-Wilk test and homogeneity of variance using a Bartlett’s test (Zar 1999; Statistix Analytical Software 2005). During the first year of the study, 2004, raw data did not conform to the assumptions for analysis of variance and were modified with a log10 transformation. Effects of insecticide applications were examined within each sample date using a one-way analysis of variance followed by a least significant difference test to sepa- rate means (Zar 1999; Statistix Analytical Software 2005). Dur- ing the second and third years of the study, 2005 and 2006, raw data did not conform to the assumptions for analysis of variance and were modified with a log10 transformation. Although this transformation corrected for normality, homogeneity of variance could not be achieved through transformations. Therefore, to 327 evaluate the efficacies of insecticides and determine if levels of control differed, we compared treatments for each date samples were collected in 2005 and 2006 with a Kruskal-Wallis nonpara- metric analysis of variance (Zar 1999; Statistix Analytical Soft- ware 2005). After the analysis, all pairwise comparison tests were used to determine which treatment means differed within each date (Statistix Analytical Software 2005). RESULTS In 2004, at least one of the insecticides significantly reduced numbers of EHS relative to untreated trees on all dates: 7 July 2004, F6,56 3.00, P < 0.01; 8 August, F6,56 6.87, P < 0.0001; 7 September, F6,56 5.15, P < 0.0001; and 7 October, F6,56 3.46, P < 0.005. Of all materials tested, pyriproxyfen provided the most reliable and prolonged levels of control (Fig- ure 2). Abundance of scale on trees treated with pyriproxyfen differed from untreated trees on all sample dates. The abundance of EHS on trees treated with horticultural oil differed from un- treated trees on two of four dates and trees treated with imida- cloprid as Merit differed from untreated trees on 7 October, the last date trees were sampled in 2004. The most dramatic differ- ence between untreated trees and those treated with insecticides occurred on 7 September when trees treated with pyriproxyfen, and horticultural oil had 98% and 95% fewer scales than un- treated trees, respectively (Figure 2). This reduction was likely the result of the destruction of scales in the first generation in June when insecticides were applied. Fewer surviving scales limited recruitment of the second generation of scales later in the year. In 2005, scale populations were highly variable and only trees treated with pyriproxyfen had significantly fewer scales than untreated trees on the sample date of 6 September, Kruskal- Figure 2. Densities of elongate hemlock scale on trees treated with Distance (pyriproxyfen), horticultural oil, Imicide (imidacloprid), Merit (imidacloprid), dinotefuran, Acecaps (acephate), and untreated (control) trees in September 2004 and 2005. Bars represent means and vertical lines are stan- dard errors. Within each year, means that share a letter do not differ by a least significant difference test (P < 0.05) (2004) or an all pairwise comparison test (P < 0.05) (2005). ©2008 International Society of Arboriculture
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