What attacks hemlock: pests and diseases the sources name

This page reports what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. Each row names its source, all read on October 9, 2026. Where this site has a full profile, the row links it, and the regulated status tables are on the linked pages and are not repeated here. The two hemlocks of North America are covered in eastern hemlock and western hemlock, from US federal sources.

The register

Agent	What the sources record
Hemlock woolly adelgid, Adelges tsugae. Full profile	Kind: Aphid-like sap-feeding insect Hosts: Natural Resources Canada says the introduced population has caused widespread death of eastern and Carolina hemlock of all ages in the eastern United States. In its native range in eastern Asia the primary host is tiger-tail spruce and several Asian hemlocks serve as secondary hosts, and a distinct lineage is native to western North America. It says the insect has little impact on local hemlocks in the native ranges. Penn State Extension says it has generally not caused severe damage in the western United States. Where and status: The Canadian Food Inspection Agency lists regulated areas, and that list is on the hemlock woolly adelgid profile. Penn State Extension lists 19 US states where it has been recorded as a pest, and says it has caused significant damage to eastern hemlock in much of Pennsylvania. Season: Penn State Extension says overwintering females lay eggs from late winter through June, eggs start hatching in early April with hatching complete by late June, and the nymphs mature by late September. The Canadian agency says the white egg sacs are most obvious in spring, and that infested trees can die within 4 to 15 years.
Elongate hemlock scale, Fiorinia externa. Full profile	Kind: Armored scale insect, introduced from Asia Hosts: Penn State Extension names eastern, Carolina and northern Japanese hemlock as principal hosts, with fir and spruce, and says it also feeds on cedar, Douglas-fir, pine and yew as less preferred hosts, usually growing next to infested hemlocks. North Carolina State Extension names hemlocks and true firs, Fraser fir among them, as the most common hosts in western North Carolina. Where and status: Penn State Extension and the University of Florida's EDIS say it was first documented in Queens, New York, in 1908, and North Carolina State puts the first introduction in New York City in 1908. North Carolina State also says it is reported in more than 14 eastern states, as far south as Georgia, and that some states regulate its import and that exports to other countries must be free of the scale. Season: Penn State Extension says it overwinters as fertilized females or eggs and females lay eggs from early spring through early summer, with eggs hatching in three to four weeks. North Carolina State says the white waxy excretions of the males are seen on the upper needle surface especially in summer.

Agent

What the sources record

Hemlock woolly adelgid, Adelges tsugae. Full profile

Kind: Aphid-like sap-feeding insect
Hosts: Natural Resources Canada says the introduced population has caused widespread death of eastern and Carolina hemlock of all ages in the eastern United States. In its native range in eastern Asia the primary host is tiger-tail spruce and several Asian hemlocks serve as secondary hosts, and a distinct lineage is native to western North America. It says the insect has little impact on local hemlocks in the native ranges. Penn State Extension says it has generally not caused severe damage in the western United States.
Where and status: The Canadian Food Inspection Agency lists regulated areas, and that list is on the hemlock woolly adelgid profile. Penn State Extension lists 19 US states where it has been recorded as a pest, and says it has caused significant damage to eastern hemlock in much of Pennsylvania.
Season: Penn State Extension says overwintering females lay eggs from late winter through June, eggs start hatching in early April with hatching complete by late June, and the nymphs mature by late September. The Canadian agency says the white egg sacs are most obvious in spring, and that infested trees can die within 4 to 15 years.

Elongate hemlock scale, Fiorinia externa. Full profile

Kind: Armored scale insect, introduced from Asia
Hosts: Penn State Extension names eastern, Carolina and northern Japanese hemlock as principal hosts, with fir and spruce, and says it also feeds on cedar, Douglas-fir, pine and yew as less preferred hosts, usually growing next to infested hemlocks. North Carolina State Extension names hemlocks and true firs, Fraser fir among them, as the most common hosts in western North Carolina.
Where and status: Penn State Extension and the University of Florida's EDIS say it was first documented in Queens, New York, in 1908, and North Carolina State puts the first introduction in New York City in 1908. North Carolina State also says it is reported in more than 14 eastern states, as far south as Georgia, and that some states regulate its import and that exports to other countries must be free of the scale.
Season: Penn State Extension says it overwinters as fertilized females or eggs and females lay eggs from early spring through early summer, with eggs hatching in three to four weeks. North Carolina State says the white waxy excretions of the males are seen on the upper needle surface especially in summer.

How the sources describe the effects

Natural Resources Canada says the adelgid feeds by inserting piercing mouthparts into the tree and sucking up nourishment, and in its introduced range on hemlock the feeding causes distortion and eventual loss of needles, twigs and stems. The Canadian Food Inspection Agency lists premature bud and shoot dieback, premature needle loss, a thinner greyish-green crown and tree death as signs. Penn State Extension says moderate populations may reduce tree health and severe ones can end in dieback or death.

The scale is sometimes mistaken for the adelgid. Penn State Extension says waxy strands from settled crawlers can be so abundant that the underside of the needles looks white, which can lead an uninformed person to take it for the adelgid. North Carolina State says heavy infestations can bring yellow blotches on needles and stunted growth, and that infestations which do not reduce growth can make Christmas trees unsaleable because of the white covering.

Profiles on this site

Both agents have full profiles: hemlock woolly adelgid and elongate hemlock scale. The sources read for this page name no hemlock disease with enough separate facts for a row.

Who the sources say to report to

The Canadian Food Inspection Agency asks that suspected hemlock woolly adelgid be reported immediately through its online form. The pages read for the scale name no report line. The reporting offices for each country are on the report a pest in Canada and report a pest in the United States pages.

What attacks hemlock: pests and diseases the sources name

The register

How the sources describe the effects

Profiles on this site

Who the sources say to report to

Sources