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