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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