Post on 21-Dec-2015
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 environment– here
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 20100
5
10
15
20
140150160170180190
Sanford
Number of -25C events in Sanford, ME
Kathleen S. Shields and Carole A. S-J. Cheah. USDA Forest Service, Hamden, CTConnecticut Agricultural Experiment Station, Windsor, CT
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?
http://www.invasive.org/hwa/
Feasibility
• Ecological– Conservation of
threatened species
• Economic– Pesticides for
ornamental and vector trees
Health Management Plan