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Rigsby, Chad M., Ian G. Kinahan, Amelia May, et al. "Impact of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) Infestation on the Jasmonic Acid-Elicited Defenses of Tsuga canadensis (Pinales: Pinaceae)." Environmental Entomology 49, no. 5 (2020): 1226–31. http://dx.doi.org/10.1093/ee/nvaa104.
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Abstract Hemlock woolly adelgid is an invasive piercing-sucking insect in eastern North America, which upon infestation of its main host, eastern hemlock (‘hemlock’), improves attraction and performance of folivorous insects on hemlock. This increased performance may be mediated by hemlock woolly adelgid feeding causing antagonism between the the jasmonic acid and other hormone pathways. In a common garden experiments using hemlock woolly adelgid infestation and induction with methyl jasmonate (MeJA) and measures of secondary metabolite contents and defense-associated enzyme activities, we explored the impact of hemlock woolly adelgid feeding on the local and systemic induction of jasmonic acid (JA)-elicited defenses. We found that in local tissue hemlock woolly adelgid or MeJA exposure resulted in unique induced phenotypes, whereas the combined treatment resulted in an induced phenotype that was a mixture of the two individual treatments. We also found that if the plant was infested with hemlock woolly adelgid, the systemic response of the plant was dominated by hemlock woolly adelgid, regardless of whether MeJA was applied. Interestingly, in the absence of hemlock woolly adelgid, hemlock plants had a very weak systemic response to MeJA. We conclude that hemlock woolly adelgid infestation prevents systemic induction of JA-elicited defenses. Taken together, compromised local JA-elicited defenses combined with weak systemic induction could be major contributors to increased folivore performance on hemlock woolly adelgid-infested hemlock.
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Evans, Daniel M., W. Michael Aust, C. Andrew Dolloff, Ben S. Templeton, and John A. Peterson. "Eastern Hemlock Decline in Riparian Areas from Maine to Alabama." Northern Journal of Applied Forestry 28, no. 2 (2011): 97–104. http://dx.doi.org/10.1093/njaf/28.2.97.
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Abstract Eastern hemlock (Tsuga canadensis) in the Appalachian mountain range is threatened by the introduced hemlock woolly adelgid (Adelges tsugae). Potential impacts on riparian systems are great because of eastern hemlock's role as a foundation species that influences site soil, vegetation, and stream characteristics. We installed permanent research sites at 49 locations in riparian areas, from Maine to Alabama, to survey eastern hemlock health, measure stand dynamics, and predict near-term forest composition without eastern hemlock. This report summarizes the initial stand measurements from summer of 2008. We found hemlock woolly adelgid present at 25 of 49 stands from Massachusetts to Georgia, and all of these stands had some degree of hemlock decline. New England states, Ohio, western Pennsylvania, Kentucky, and Alabama had good hemlock health and no sign of hemlock woolly adelgid. Eighteen of the 49 sites had no nonhemlock conifer species in the overstory, and 30 of 49 sites had less than 5 m2 ha−1 of nonhemlock conifers. Without eastern hemlock, 25 of the stands would have more than 90% hardwood in the overstory, many of which are in the mid-Atlantic and southern states at sites dominated by shrubs in the understory such as Rhododendron maximum. Competition from shrubs may hinder stand regeneration after disturbance by hemlock woolly adelgid. On the basis of the abundance of hardwood species and lack of conifer species present in the overstory at many infested hemlock-dominated stands, these sites may convert to hardwood-dominated stands, which will affect terrestrial and aquatic ecosystem dynamics.
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Fajvan, Mary Ann, and Randall S. Morin. "Spatial Distribution of Chesapeake Bay Riparian Hemlock Forests Threatened by Hemlock Woolly Adelgid." Journal of Forestry 119, no. 3 (2021): 219–28. http://dx.doi.org/10.1093/jofore/fvab001.
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Abstract Landscape-scale maps of tree species densities are important tools for managing ecosystems threatened by forest pests. Eastern hemlock dominates riparian forests throughout its range. As a conifer in a deciduous landscape, hemlock plays an ecohydrological role, especially when other species are dormant. The nonnative, hemlock woolly adelgid has caused widespread hemlock decline and mortality. We used two existing basal area raster layers first to identify Chesapeake Bay subwatersheds with ≥6 percent hemlock basal area and second to quantify hemlock basal area densities within fixed-width riparian buffers of 50 m, 100 m, 250 m, and 500 m. Hemlock densities were higher in riparian zones compared with entire subwatersheds. In five subwatersheds, 50 m and 100 m zones had higher percentages of pixels with ≥25 percent hemlock basal area. We produced maps identifying hemlock riparian densities in the Pine Creek Watershed, which managers can use to prioritize sites for supplemental conifer planting under anticipated hemlock decline.
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Cleavitt, Natalie L., Anne K. Eschtruth, John J. Battles, and Timothy J. Fahey. "Bryophyte response to eastern hemlock decline caused by hemlock woolly adelgid infestation1." Journal of the Torrey Botanical Society 135, no. 1 (2008): 12–25. http://dx.doi.org/10.3159/07-ra-030.1.
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Oten, K. L. F., G. R. Bauchan, J. Frampton, and F. P. Hain. "Biophysical characteristics of the stem and petiole surface of six hemlock (Tsuga) species and a hybrid: implications for resistance to Adelges tsugae." Botany 90, no. 11 (2012): 1170–78. http://dx.doi.org/10.1139/b2012-095.
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Characteristics of the plant surface significantly affect host-plant selection by phytophagous insects. Surface morphology of six hemlock species (Tsuga spp.) and a hybrid was investigated using low-temperature scanning electron microscopy. Observations focused on trichome presence and placement and cuticle thickness. These characteristics were studied in the context of species-level host-plant resistance to the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), an exotic insect causing massive mortality to eastern hemlocks (Tsuga canadensis (L.) Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) in the eastern United States. Hemlocks in the native range of the insect do not succumb to infestations and the mechanism of resistance is unknown. We addressed the potential role of plant surface morphology in the adelgid–hemlock interaction by comparing four adelgid-resistant hemlock species and a hybrid with the two adelgid-susceptible hemlock species. We found that trichomes are likely not involved in conferring resistance to A. tsugae. Cuticle thickness may be involved in insertion site selection by A. tsugae and may therefore have implications for resistance. The cuticle is thinnest at the point of A. tsugae stylet insertion and thus may affect A. tsugae feeding.
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Churchel, Melissa A., James L. Hanula, C. Wayne Berisford, James M. Vose, and Mark J. Dalusky. "Impact of Imidacloprid for Control of Hemlock Woolly Adelgid on Nearby Aquatic Macroinvertebrate Assemblages." Southern Journal of Applied Forestry 35, no. 1 (2011): 26–32. http://dx.doi.org/10.1093/sjaf/35.1.26.
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Abstract Imidacloprid, a systemic insecticide that acts on the nervous system, is currently being used to control hemlock woolly adelgid (Adelges tsugae Annand), which is damaging hemlock trees. The objective of this study was to determine whether soil injection with imidacloprid for hemlock woolly adelgid control near streams adversely affects aquatic invertebrates. Eastern hemlocks (Tsuga canadensis) in the watersheds surrounding four streams in the southern Appalachian region of Georgia and North Carolina were treated with imidacloprid. Addie Branch was the only stream that exhibited a possible effect from imidacloprid treatment. However, the data followed the same pattern as the other treatment streams, but with a more pronounced decrease in taxa due to adult emergence. Only a trace amount of imidacloprid was detected in one water sample from Holcomb Tributary over a period of 2 years, and no effect was observed on the aquatic macroinvertebrates in that stream. However, caution should be used when applying these results to other areas with different soil types (e.g., low organic matter content) that may not bind imidacloprid as tightly. Our results indicate that soil injections of imidacloprid can safely be used in the southern Appalachian area to control hemlock woolly adelgid.
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Dampier, Jason Ernest Elvin, Richard W. Harper, Ashley McElhinney, and Eric Biltonen. "Modeling Benefit–cost Analysis of Hemlock Wooly Adelgid Host Plant Resistance with Emphasis on Least-toxic Chemical Treatment Alternatives." HortTechnology 28, no. 5 (2018): 624–28. http://dx.doi.org/10.21273/horttech04080-18.
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Chinese hemlock (Tsuga chinensis) exhibits a high level of resistance to the exotic insect hemlock woolly adelgid (HWA; Adelges tsugae) relative to the native and widely planted eastern hemlock (Tsuga canadensis). Furthermore, both chinese and eastern hemlock exhibit similar autecologic and aesthetic characteristics in urban and suburban environments. This study provides a comparative 25-year economic benefit-cost analysis (BCA), tracking estimated establishment and insect control costs for the two tree species. Eastern hemlock survival requires insecticide treatments when growing within the range of HWA. Insect control scenarios used and evaluated in this study include annual horticultural oil spray, biannual horticultural oil spray, biennial imidacloprid soil drench, and no treatment. The chinese hemlock scenario did not include chemical insect control because of the species’ host plant resistance (HPR) to HWA. Benefits were estimated using the U.S. Department of Agriculture, Forest Service’s i-Tree tool, which estimates economic benefits for ecosystem services (expressed in dollars). Benefit–cost ratios (BCRs) were developed using the present value for 25-year benefit and cost streams at 2% and 4% discount rates. Payback periods were also estimated for all options that had a calculated BCR greater than one. The benefit–cost analyses for each insect control scenario were evaluated, compared, and assessed through the lens of market potential. The costs exceed the benefits for all of the eastern hemlock scenarios. The benefits exceed costs for the chinese hemlock scenario. Results suggest that chinese hemlock is a viable alternative to eastern hemlock in view of its HPR and reduced associated costs over time. If chinese hemlock becomes more widely planted, it is expected to produce greater BCRs relative to chemical control options as a result of the lack of required, ongoing insect control treatment costs.
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Domec, Jean-Christophe, Laura N. Rivera, John S. King, et al. "Hemlock woolly adelgid (Adelges tsugae) infestation affects water and carbon relations of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana)." New Phytologist 199, no. 2 (2013): 452–63. http://dx.doi.org/10.1111/nph.12263.
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Austin, David A., Saskia L. van de Gevel, and Peter T. Soulé. "Forest dynamics and climate sensitivity of an endangered Carolina hemlock community in the southern Appalachian Mountains, USA." Botany 94, no. 4 (2016): 301–9. http://dx.doi.org/10.1139/cjb-2015-0222.
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During the last century, the eastern United States has functionally lost two major tree species (American chestnut and American elm), two more, eastern and Carolina hemlock, will likely be functionally extinct during much of their ranges by 2050. Carolina hemlock forests are geographically limited to high elevations in the southern Appalachian Mountains and are considered to be endangered. We collected forest stand, composition, and tree age data at the beginning of a hemlock woolly adelgid (HWA) infestation. Prior to the arrival of HWA, Carolina hemlocks were healthy and densely populated in the overstory and understory. While Carolina hemlock regenerated successfully and continuously from 1850 to 2010, the development of this Carolina hemlock forest will be altered by the HWA and may result in an increase in the density of northern red oak, white oak, mountain laurel, and Catawba rhododendron. Carolina hemlocks prefer cool, wet summers with older trees experiencing greater reductions in radial growth than younger trees during droughts. This study demonstrates that dendrochronological techniques can provide critical annual information on Carolina hemlock forest development and tree age–climate response. Our results provide a multicentury perspective for conservation efforts and management of Carolina hemlock forests in the southern Appalachian Mountains.
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Huggett, Brett A., Jessica A. Savage, Guang-You Hao, Evan L. Preisser, and N. Michele Holbrook. "Impact of hemlock woolly adelgid (Adelges tsugae) infestation on xylem structure and function and leaf physiology in eastern hemlock (Tsuga canadensis)." Functional Plant Biology 45, no. 5 (2018): 501. http://dx.doi.org/10.1071/fp17233.
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Hemlock woolly adelgid (Adelges tsugae Annand) (HWA) is an invasive insect that feeds upon the foliage of eastern hemlock (Tsuga canadensis (L.) Carrière) trees, leading to a decline in health and often mortality. The exact mechanism leading to the demise of eastern hemlocks remains uncertain because little is known about how HWA infestation directly alters the host’s physiology. To evaluate the physiological responses of eastern hemlock during early infestation of HWA, we measured needle loss, xylem hydraulic conductivity, vulnerability to cavitation, tracheid anatomy, leaf-level gas exchange, leaf water potential and foliar cation and nutrient levels on HWA-infested and noninfested even-aged trees in an experimental garden. HWA infestation resulted in higher xylem hydraulic conductivity correlated with an increase in average tracheid lumen area and no difference in vulnerability to cavitation, indicating that needle loss associated with HWA infestation could not be attributed to reduced xylem transport capacity. HWA-infested trees exhibited higher rates of net photosynthesis and significant changes in foliar nutrient partitioning, but showed no differences in branch increment growth rates compared with noninfested trees. This study suggests that HWA-induced decline in the health of eastern hemlock trees is not initially caused by compromised water relations or needle loss.
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Garris, Heath W., Thomas H. Settle, Jonathan E. Crossman, Stephen J. Grider, and Shawnté L. Michaels. "Combined Effects of Hemlock Woolly Adelgid (Adelges tsugae) Infestation and Treatment with Imidacloprid on Eastern Hemlock (Tsuga canadensis) Leaf Radiometry." Journal of Forestry 117, no. 4 (2019): 340–50. http://dx.doi.org/10.1093/jofore/fvz021.
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Abstract The neonicotinoid systemic insecticide imidacloprid has proven to be an effective treatment for the prevention and control of hemlock woolly adelgid (Adelges tsugae Annand) in southeastern populations of eastern hemlock (Tsuga canadensis L.). Recent studies have demonstrated that imidacloprid and A. tsugae both stimulate salicylic acid-dependent physiological responses in plant tissues responsible for plant defenses against pathogens, timing of developmental outcomes including flowering and leaf senescence, and resilience to abiotic stressors. We evaluated the interacting effects of A. tsugae presence/absence and treatment with imidacloprid on leaf optical properties indicative of photosynthetic potential, photosynthetic efficiency, and tissue senescence. Our results indicated that A. tsugae changes lower canopy leaf optical properties indicative of reduced photosynthetic potential/efficiency and accelerated senescence in mature leaves. Imidacloprid was associated with declines in photosynthetic potential and showed a largely similar, though less pronounced, effect on leaf spectral properties to that of A. tsugae.
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Mahan, Carolyn, Kristi L. Sullivan, Byran Black, Ke Chung Kim, and Richard H. Yahner. "Overstory Tree Composition of Eastern Hemlock Stands Threatened by the Hemlock Woolly Adelgid at Delaware Water Gap National Recreation Area." Castanea 69, no. 1 (2004): 30–37. http://dx.doi.org/10.2179/0008-7475(2004)069<0030:otcoeh>2.0.co;2.
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Kinahan, Ian G., Chad M. Rigsby, Suzanne K. Savage, et al. "Seasonal changes in eastern hemlock (Tsuga canadensis) foliar chemistry." Canadian Journal of Forest Research 50, no. 6 (2020): 557–64. http://dx.doi.org/10.1139/cjfr-2019-0408.
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Eastern hemlock (Tsuga canadensis (L.) Carrière) is an eastern North American conifer threatened by the invasive hemlock woolly adelgid (Adelges tsugae Annand). Changes in foliar terpenes and phenolics were evaluated in new (current-year growth) and mature (1-year-old growth) hemlock needles during the growing season and into plant dormancy. From April through September, foliar concentrations of nonvolatile soluble phenolics, condensed tannins, lignin, mono- and sesquiterpenes, α-pinene, camphene, isobornyl acetate, and diterpene resin were quantified. After September, additional analyses of metabolites that continued to differ significantly between new and mature foliage were carried out. Total soluble phenolic and condensed tannin concentrations in new foliage remained low relative to those of mature foliage throughout the growing season and converged in December. Lignin concentration in new foliage converged with that of mature foliage by July. Concentrations of α-pinene, camphene, isobornyl acetate, and diterpene resin in new foliage converged with those of mature foliage within 1 month of budbreak. The convergence of terpene concentrations in new and mature foliage suggests that these metabolites may play a role in herbivore defense during the peak growing season. Conversely, soluble phenolics, including condensed tannins, may defend foliage from herbivory outside of the spring growth period.
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Boucher, Peter Brehm, Steven Hancock, David A. Orwig, et al. "Detecting Change in Forest Structure with Simulated GEDI Lidar Waveforms: A Case Study of the Hemlock Woolly Adelgid (HWA; Adelges tsugae) Infestation." Remote Sensing 12, no. 8 (2020): 1304. http://dx.doi.org/10.3390/rs12081304.
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The hemlock woolly adelgid (HWA; Adelges tsugae) is an invasive insect infestation that is spreading into the forests of the northeastern United States, driven by the warmer winter temperatures associated with climate change. The initial stages of this disturbance are difficult to detect with passive optical remote sensing, since the insect often causes its host species, eastern hemlock trees (Tsuga canadensis), to defoliate in the midstory and understory before showing impacts in the overstory. New active remote sensing technologies—such as the recently launched NASA Global Ecosystem Dynamics Investigation (GEDI) spaceborne lidar—can address this limitation by penetrating canopy gaps and recording lower canopy structural changes. This study explores new opportunities for monitoring the HWA infestation with airborne lidar scanning (ALS) and GEDI spaceborne lidar data. GEDI waveforms were simulated using airborne lidar datasets from an HWA-infested forest plot at the Harvard Forest ForestGEO site in central Massachusetts. Two airborne lidar instruments, the NASA G-LiHT and the NEON AOP, overflew the site in 2012 and 2016. GEDI waveforms were simulated from each airborne lidar dataset, and the change in waveform metrics from 2012 to 2016 was compared to field-derived hemlock mortality at the ForestGEO site. Hemlock plots were shown to be undergoing dynamic changes as a result of the HWA infestation, losing substantial plant area in the middle canopy, while still growing in the upper canopy. Changes in midstory plant area (PAI 11–12 m above ground) and overall canopy permeability (indicated by RH10) accounted for 60% of the variation in hemlock mortality in a logistic regression model. The robustness of these structure-condition relationships held even when simulated waveforms were treated as real GEDI data with added noise and sparse spatial coverage. These results show promise for future disturbance monitoring studies with ALS and GEDI lidar data.
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Toland, Ashley, Carlyle Brewster, Katlin Mooneyham, and Scott Salom. "First Report on Establishment of Laricobius osakensis (Coleoptera: Derodontidae), a Biological Control Agent for Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae), in the Eastern U.S." Forests 9, no. 8 (2018): 496. http://dx.doi.org/10.3390/f9080496.
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The hemlock woolly adelgid (HWA) is an invasive insect species native to Japan causing significant hemlock mortality in the eastern United States. Laricobius spp. have been targeted as biological control agents because they are adelgid specialists. Laricobius osakensis Montgomery and Shiyake is native to the same region of Japan from which the strain of HWA found in the eastern United States originated. Studies in Japan found that it is phenologically synchronous with HWA. Following approval to release L. osakensis from quarantine in 2010, approximately 32,000 were released at a total of 61 sites starting in 2012. In winter of 2014 and 2015, periods of extreme cold temperatures throughout the eastern USA, as well as the polar vortex, resulted in extensive mortality to HWA, which likely delayed the establishment of L. osakensis. The ability of the beetle to survive and establish in the eastern United States is reported here. In the first year of this study (2015–2016), limited numbers of L. osakensis were recovered, as HWA populations were still rebounding. In the second year (2016–2017), 147 L. osakensis were collected at 5 of 9 sites sampled, coinciding with rebounding HWA populations. Larval recovery was much greater than adult recovery throughout the study. HWA density was directly correlated with warmer plant hardiness zones and recovery of Laricobius beetles was significantly correlated with HWA density. Our results suggest that L. osakensis is successfully establishing at several of the sampled release sites and that the best predictor of its presence at a site is the HWA density.
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Stanosz, G. R., D. R. Smith, J. P. Sullivan, et al. "Shoot Blight Caused by Sirococcus tsugae on Eastern Hemlock (Tsuga canadensis) in Georgia." Plant Disease 95, no. 5 (2011): 612. http://dx.doi.org/10.1094/pdis-11-10-0833.
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Eastern hemlock (Tsuga canadensis) is an ecologically and economically important conifer from the north-central United States to the east coast of North America to the southern Appalachian Mountains. In early spring 2010, blighted shoot tips of eastern hemlock were observed at widely separated locations in the Chattahoochee National Forest in north Georgia. Damage did not appear to be directly related to hemlock woolly adelgid (Adelges tsugae) activity, which was sporadic or absent in some areas where symptoms were observed. A preliminary survey in March 2010 revealed that incidence of blighted shoots on individual trees varied, but was as high as 70%. Stems of shoots produced the previous year were frequently necrotic, had lost needles, and bore pycnidia with hyaline, two-celled conidia consistent with those of Sirococcus tsugae (2,3). Later in the spring and summer, shoots of the current year's growth became blighted, with sporulation of S. tsugae also on dead and dying needles. While S. tsugae previously has been reported on T. heterophylla, T. mertensiana, Cedrus atlantica, and C. deodara in western North America, it has only recently been reported on eastern hemlock (1), and its ability to induce shoot blight has not been proven. Pure cultures (2,3) were obtained on streptomycin-amended potato dextrose agar (PDA) and their identity was confirmed by species-specific PCR primers (4). Nuclear rDNA internal transcribed spacer sequence (554 nucleotides) also was obtained for isolate 10-05 and deposited in GenBank (Accession No. HQ256769). This sequence was found to be identical to sequences previously deposited for S. tsugae isolates. Isolate 10-05 and a second isolate (10-06) were used to inoculate potted 2-year-old eastern hemlock seedlings in a growth chamber at 20°C with a 16-h photoperiod. Conidia were collected by flooding 1-month-old colonies on PDA with sterile water. Expanding shoots on one branch of each seedling were wounded using scissors to cut the tips off needles and stems, while another branch remained nonwounded. Ten seedlings per isolate were inoculated by spraying to runoff with a suspension of 5 × 106 conidia ml–1 in sterile water, and five similarly treated control seedlings were sprayed with sterile water. Seedlings were covered with plastic bags to maintain high humidity for 4 days. Germination of conidia of each isolate incubated on water agar in this growth chamber was >80% after 24 h. Symptoms were evaluated and reisolation was attempted on streptomycin-amended PDA 2 months after inoculation. Symptoms of seedlings inoculated with either isolate included chlorotic and necrotic needle spots, browning of cut edges of needles, browning and death of needle tips and entire needles, death of stem tips with retention of dead needles, and needle loss. Symptoms of control seedlings were limited to slight browning of cut edges of needles. The fungus was reisolated from wounded shoots of 17 of 20 inoculated seedlings and nonwounded shoots of 5 of 20 inoculated seedlings and was not cultured from control seedlings. To our knowledge, this is the first report of S. tsugae in Georgia and also the first demonstration of its ability to produce symptoms that have been attributed to it on any tree species. References: (1) M. Miller-Weeks and W. Ostrofsky. USDA. Forest Service. Online publication. NA-PR-01-10, 2010. (2) A. Y. Rossman et al. For. Pathol. 38:47. (3) D. R. Smith et al. For. Pathol. 33:141, 2003. (4) D. R. Smith and G. R. Stanosz. For. Pathol. 38:156, 2008.
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Dukes, Jeffrey S., Jennifer Pontius, David Orwig, et al. "Responses of insect pests, pathogens, and invasive plant species to climate change in the forests of northeastern North America: What can we predict?This article is one of a selection of papers from NE Forests 2100: A Synthesis of Climate Change Impacts on Forests of the Northeastern US and Eastern Canada." Canadian Journal of Forest Research 39, no. 2 (2009): 231–48. http://dx.doi.org/10.1139/x08-171.
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Climate models project that by 2100, the northeastern US and eastern Canada will warm by approximately 3–5 °C, with increased winter precipitation. These changes will affect trees directly and also indirectly through effects on “nuisance” species, such as insect pests, pathogens, and invasive plants. We review how basic ecological principles can be used to predict nuisance species’ responses to climate change and how this is likely to impact northeastern forests. We then examine in detail the potential responses of two pest species (hemlock woolly adelgid ( Adelges tsugae Annand) and forest tent caterpillar ( Malacosoma disstria Hubner)), two pathogens (armillaria root rot ( Armillaria spp.) and beech bark disease ( Cryptococcus fagisuga Lind. + Neonectria spp.)), and two invasive plant species (glossy buckthorn ( Frangula alnus Mill.) and oriental bittersweet ( Celastrus orbiculatus Thunb.)). Several of these species are likely to have stronger or more widespread effects on forest composition and structure under the projected climate. However, uncertainty pervades our predictions because we lack adequate data on the species and because some species depend on complex, incompletely understood, unstable relationships. While targeted research will increase our confidence in making predictions, some uncertainty will always persist. Therefore, we encourage policies that allow for this uncertainty by considering a wide range of possible scenarios.
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Harper, Richard, and Paul Weston. "Potential of Alternative Tsuga spp. as Landscape Replacements for T. canadensis: Longer-Term Evaluation and Propagation of T. chinensis." Arboriculture & Urban Forestry 42, no. 5 (2016). http://dx.doi.org/10.48044/jauf.2016.030.
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Seven species of hemlock (Tsuga spp.)—four from North America and three from Asia—were evaluated in replicated plots in Katonah, New York, United States (USDA Plant Hardiness Zone 6b) as potential replacements for eastern hemlock (Tsuga canadensis), which is gradually being extirpated from landscapes in the eastern United States. by the invasive hemlock woolly adelgid (Adelges tsugae). Trends reported in an earlier study (Weston and Harper 2009) continued but were exaggerated after an additional three years of observation. For example, Chinese hemlock (T. chinensis) continued to show the greatest potential as a replacement for T. canadensis as mortality was very low, overall plant health was exceptional, and tolerance to A. tsugae was robust. Early indicators suggest that T. chinensis may also be readily propagated from hardwood cuttings under appropriate greenhouse conditions. These characteristics suggest that T. chinensis may indeed become a viable replacement for T. canadensis, and a valuable addition to landscapes in the eastern U.S.