Transcript HWA
Decline of Eastern Hemlock due to Hemlock Woolly Adelgid Sophia DeMaio April 25, 2007 Susceptible Species • Carolina (Tsuga caroliniana) and eastern hemlock (Tsuga canadensis) • Western (T. heterophylla) and mountain hemlock (T.mertensiana) also become invested but do not decline Eastern Hemlock • Range: Great Lakes to New England • Cool, moist climates • Acidic soils • Very shade tolerant • Long-lived Eastern Hemlock Importance • Economic – – – – Tanning Lumber Pulp Ornamental varieties • Ecological – – – – – Dense canopies Vertical structure Horizontal structure Nutrient cycling Ecological research Symptoms • Needles dry • Turn grayish green or yellow • Thinning of foliage • Crown and branch dieback Forest Impacts • Tolerant conifer replaced by hardwoods – – – – – Stand structure Stand density Microclimate Wildlife habitat Nutrient cycling Primary Stress • Hemlock woolly adelgid (HWA; Adelges tsugae) • Signs: fuzzy white spots underside of needles, late fall-early summer, crawlers spring and summer • Introduced from southern Japan to NJ->New England->Maine • Limited by T (39F spring generation, -25F winter generation) and vectors Predisposing factors • Warm winters • Introduced pest – No time for tree to adapt or predator populations to build • Drought – Low precipitation (especially in summer) – Drought-prone sites (shallow rooting, southern slopes) • Other hemlock stressors Life Cycle • Winter generation – Eggs hatch mid-summer • ~300 per adult – Crawler enter summer dormancy late summer • all adults are female=parthenogenesis) • Only moving and exposed stage • Find feeding sites on twigs – Resume development in October (2,3,4 instar nymphs) • Feed in place • White woolly covering • Spring generation – Eggs hatch early spring (20-75/adult) – Reach adulthood early summer • Some winged adults fly to alternate host (not available so die, but keep populations viable) • Density dependent population growth Mechanisms for disruption • Depletes tree’s starch reserves – Inserts stylet into xylem ray parenchyma – starves to death • allocates E to external new shoots • New growth reinfested Population control • Early freezing (spring generation) • Cold winters (-25) with little snow (overwintering sistens) • Predation – Native Number of -25Cenvironment events in Sanford, ME 20 15 10 –Sanford here 5 Kathleen S. Shields and Carole A. S-J. Cheah. USDA Forest Service, Hamden, CT Connecticut Agricultural Experiment Station, Windsor, CT 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 190 180 170 160 150 140 2010 Inciting factors • Transport of eggs or crawlers to suitable feeding site – Spread by wildlife, human activities, wind • HWA Feeding and reproduction Contributing factors • Drought • Fungal infection • Other insect pests and diseases – Elongate hemlock scale – Hemlock looper – Spruce spider mite – Hemlock borer – needlerust Control-preemptive • Quarantine • Increase hemlock vigor (5 yrs before infestation) • Manage for white pine over hemlock in drought-prone sites • Decrease spread by vectors Monitor and Survey • Public outreach education – Take a stand • Costa protocol Reactive control-Chemical and physical • Horticultural oils – suffocates adelgid – minimal impact other forest trees – widely spaced, manageable height • Stem/root injection – concentrated chemical – Systematic – drilling may further stress tree • Soil injection – Problem near streams – Soil organisms • • Harvest vector trees Salvage – Plant with white pine or other intermediate species on good sites Reactive control-biological • Beetles – Sasajiscymnus tsugae – Scymnus – Laricobius nigrinus • Fungi – – – – Beauveria bassiana Metarhizium anisopliae Verticillium lecanii Paecilomyces sp. • Ideal? Feasibility • Ecological – Conservation of threatened species • Economic – Pesticides for ornamental and vector trees Health Management Plan