Hemlock Woolly Adelgid in New Hampshire
MODERATEInsect
Hemlock Woolly Adelgid is currently active in New Hampshire. Watch your susceptible trees closely and act early.
About Hemlock Woolly Adelgid
A tiny aphid-like insect native to Asia that feeds on hemlock sap at the base of needles. It has devastated eastern hemlock populations from Georgia to Maine. Trees typically die within 4-10 years of infestation.
Symptoms to watch for
White woolly egg sacs at the base of needles on the undersides of branches, grayish-green needle discoloration, premature needle drop, thinning canopy, branch dieback
Trees at risk in New Hampshire
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Treatment options
Imidacloprid Soil Drench
Systemic insecticide applied as a soil drench around the base of hemlocks in fall or early spring. Effective for individual landscape trees but impractical for large forest stands.
Predator Beetle Release (Laricobius nigrinus)
Release of the predator beetle Laricobius nigrinus from western North America, which feeds on HWA during winter months. USFS has released millions across the eastern range of hemlock.
Horticultural Oil Spray
Dormant oil sprayed directly on infested branches to smother adelgids. Effective on small, accessible trees. Requires thorough coverage and may need repeated application.
Recommended Products & Tools
Helpful supplies for managing Hemlock Woolly Adelgid. Always read and follow label directions, and confirm a diagnosis before treating.
Knocks down soft-bodied pests like aphids, mites, and scale crawlers.
Smothers overwintering eggs and crawlers; dormant or summer rates.
Soil-applied protection taken up by the tree for season-long control.
Sharp, clean cuts to remove affected wood — a tree-care essential.
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Browse all New Hampshire arborists →Frequently asked questions
Is Hemlock Woolly Adelgid in New Hampshire?
Hemlock Woolly Adelgid is currently active in New Hampshire. Watch your susceptible trees closely and act early.
What does Hemlock Woolly Adelgid look like?
White woolly egg sacs at the base of needles on the undersides of branches, grayish-green needle discoloration, premature needle drop, thinning canopy, branch dieback
What trees does Hemlock Woolly Adelgid affect in New Hampshire?
It affects Eastern Hemlock, Western Hemlock. Susceptibility varies by species.
How do I treat Hemlock Woolly Adelgid?
Options include: Imidacloprid Soil Drench, Predator Beetle Release (Laricobius nigrinus), Horticultural Oil Spray. Confirm the diagnosis before treating, and consider a certified arborist for high-value trees.